love triangle research paper

HYPOTHESIS AND THEORY article

Towards a comprehensive theory of love: the quadruple theory.

• Independent Researcher, San Diego, CA, United States

Scholars across an array of disciplines including social psychologists have been trying to explain the meaning of love for over a century but its polysemous nature has made it difficult to fully understand. In this paper, a quadruple framework of attraction, resonance or connection, trust, and respect are proposed to explain the meaning of love. The framework is used to explain how love grows and dies and to describe brand love, romantic love, and parental love. The synergistic relationship between the factors and how their variations modulate the intensity or levels of love are discussed.

Introduction

Scholars across an array of disciplines have tried to define the meaning and nature of love with some success but questions remain. Indeed, it has been described as a propensity to think, feel, and behave positively toward another ( Hendrick and Hendrick, 1986 ). However, the application of this approach has been unsuccessful in all forms of love ( Berscheid, 2010 ). Some social psychologists have tried to define love using psychometric techniques. Robert Sternberg Triangular Theory of Love and Clyde and Susan Hendrick’s Love Attitudes Scale (LAS) are notable attempts to employ the psychometric approach ( Hendrick and Hendrick, 1986 ; Sternberg, 1986 ). However, data analysis from the administration of the LAS, Sternberg’s scale and the Passionate Love Scale by Hatfield and Sprecher’s (1986) found a poor association with all forms of love ( Hendrick and Hendrick, 1989 ). Other studies have found a poor correlation between these and other love scales with different types of love ( Whitley, 1993 ; Sternberg, 1997 ; Masuda, 2003 ; Graham and Christiansen, 2009 ).

In recent years, the neuropsychological approach to study the nature of love has gained prominence. Research has compared the brain activity of people who were deeply in love while viewing a picture of their partner and friends of the same age using functional magnetic resonance imaging (fMRI) and concluded that there is a specialized network of the brain involved in love ( Bartels and Zeki, 2000 ). Indeed, several lines of investigation using fMRI have described a specialized area of the brain mediating maternal love ( Noriuchi et al., 2008 ; Noriuchi and Kikuchi, 2013 ) and, fMRI studies have implicated multiple brain systems particularly the reward system in romantic love ( Aron et al., 2005 ; Fisher et al., 2005 , 2010 ; Beauregard et al., 2009 ). Brain regions including ventral tegmental area, anterior insula, ventral striatum, and supplementary motor area have been demonstrated to mediate social and material reward anticipation ( Gu et al., 2019 ). Although brain imaging provides a unique insight into the nature of love, making sense of the psychological significance or inference of fMRI data is problematic ( Cacioppo et al., 2003 ).

Also, there has been growing interests in the neurobiology of love. Indeed, evidence suggests possible roles for oxytocin, vasopressin, dopamine, serotonin, testosterone, cortisol, morphinergic system, and nerve growth factor in love and attachment ( Esch and Stefano, 2005 ; De Boer et al., 2012 ; Seshadri, 2016 ; Feldman, 2017 ). However, in many cases, definite proof is still lacking and the few imaging studies on love are limited by selection bias on the duration of a love affair, gender and cultural differences ( De Boer et al., 2012 ).

So, while advances have been made in unraveling the meaning of love, questions remain and a framework that can be employed to understand love in all its forms remains to be developed or proposed. The objective of this article is to propose a novel framework that can be applied to all forms of love.

Theoretical Background and Hypothesis Development (The AAC Model)

In the past few decades, the psychological literature has defined and described different forms of love and from these descriptions, the role of attraction, attachment-commitment, and caregiving (AAC), appears to be consistent in all forms of love.

Attraction theory is one of the first approaches to explain the phenomenon of love and several studies and scholarly works have described the importance of attraction in different forms of love ( Byrne and Griffitt, 1973 ; Berscheid and Hatfield, 1978 ; Fisher et al., 2006 ; Braxton-Davis, 2010 ; Grant-Jacob, 2016 ). Attraction has been described as an evolutionary adaptation of humans for mating, reproduction, and parenting ( Fisher et al., 2002a , 2006 ).

The role of attachment in love has also been extensively investigated. Attachment bonds have been described as a critical feature of mammals including parent-infant, pair-bonds, conspecifics, and peers ( Feldman, 2017 ). Indeed, neural networks including the interaction of oxytocin and dopamine in the striatum have been implicated in attachment bonds ( Feldman, 2017 ). The key features of attachment include proximity maintenance, safety and security, and separation distress ( Berscheid, 2010 ). Multiple lines of research have proposed that humans possess an innate behavioral system of attachment that is essential in love ( Harlow, 1958 ; Bowlby, 1977 , 1988 , 1989 ; Ainsworth, 1985 ; Hazan and Shaver, 1987 ; Bretherton, 1992 ; Carter, 1998 ; Burkett and Young, 2012 ). Attachment is essential to commitment and satisfaction in a relationship ( Péloquin et al., 2013 ) and commitment leads to greater intimacy ( Sternberg, 1986 ).

Also, several lines of evidence have described the role of caregiving in love. It has been proposed that humans possess an inborn caregiving system that complements their attachment system ( Bowlby, 1973 ; Ainsworth, 1985 ). Indeed, several studies have used caregiving scale and compassionate love scale, to describe the role of caring, concern, tenderness, supporting, helping, and understanding the other(s), in love and relationships ( Kunce and Shaver, 1994 ; Sprecher and Fehr, 2005 ). Mutual communally responsive relationships in which partners attend to one another’s needs and welfare with the expectation that the other will return the favor when their own needs arise ( Clark and Mills, 1979 ; Clark and Monin, 2006 ), have been described as key in all types of relationships including friendship, family, and romantic and compassionate love ( Berscheid, 2010 ).

Attachment and caregiving reinforce each other in relationships. Evidence suggests that sustained caregiving is frequently accompanied by the growth of familiarity between the caregiver and the receiver ( Bowlby, 1989 , p. 115) strengthening attachment ( Berscheid, 2010 ). Several studies have proposed that attachment has a positive influence on caregiving behavior in love and relationships ( Carnelley et al., 1996 ; Collins and Feeney, 2000 ; Feeney and Collins, 2001 ; Mikulincer, 2006 ; Canterberry and Gillath, 2012 ; Péloquin et al., 2013 ).

The AAC model can be seen across the literature on love. Robert Sternberg triangular theory of love which proposes that love has three components —intimacy, passion, and commitment ( Sternberg, 1986 ), essentially applies the AAC model. Passion, a key factor in his theory, is associated with attraction ( Berscheid and Hatfield, 1978 ), and many passionate behaviors including increased energy, focused attention, intrusive thinking, obsessive following, possessive mate guarding, goal-oriented behaviors and motivation to win and keep a preferred mating partner ( Fisher et al., 2002b , 2006 ; Fisher, 2005 ). Also, evidence indicates that attachment is central to intimacy, another pillar of the triangular theory ( Morris, 1982 ; Feeney and Noller, 1990 ; Oleson, 1996 ; Grabill and Kent, 2000 ). Commitment, the last pillar of the triangular theory, is based on interdependence and social exchange theories ( Stanley et al., 2010 ), which is connected to mutual caregiving and secure attachment.

Hendrick and Hendrick’s (1986) , Love Attitudes Scale (LAS) which measures six types of love ( Hendrick and Hendrick, 1986 ) is at its core based on the AAC model. Similarly, numerous works on love ( Rubin, 1970 ; Hatfield and Sprecher, 1986 ; Fehr, 1994 ; Grote and Frieze, 1994 ), have applied one or all of the factors in the ACC model. Berscheid (2010) , proposed four candidates for a temporal model of love including companionate love, romantic love, and compassionate love and adult attachment love. As described, these different types of love (romantic, companionate, compassionate, and attachment) all apply at least one or all of the factors in the AAC model.

New Theory (The Quadruple Framework)

The AAC model can be fully captured by four fundamental factors; attraction, connection or resonance, trust, and respect, providing a novel framework that could explain love in all its forms. Table 1 shows the core factors of love, and the four factors derived from them.

Table 1. Factors of love.

Evidence suggests that both attachment and attraction play a role in obsession or passion observed in love ( Fisher et al., 2005 ; Honari and Saremi, 2015 ). Attraction is influenced by the value or appeal perceived from a relationship and this affects commitment ( Rusbult, 1980 ).

Connection or Resonance

Connection is key to commitment, caregiving, and intimacy. It creates a sense of oneness in relationships and it is strengthened by proximity, familiarity, similarity, and positive shared experiences ( Sullivan et al., 2011 ; Beckes et al., 2013 ). Homogeneity or similarity has been observed to increase social capital and engagement among people ( Costa and Kahn, 2003a , b ), and it has been described as foundational to human relationships ( Tobore, 2018 , pp. 6–13). Research indicates that similarity plays a key role in attachment and companionship as people are more likely to form long-lasting and successful relationships with those who are more similar to themselves ( Burgess and Wallin, 1954 ; Byrne, 1971 ; Berscheid and Reis, 1998 ; Lutz-Zois et al., 2006 ). Proximity plays a key role in caregiving as people are more likely to show compassion to those they are familiar with or those closest to them ( Sprecher and Fehr, 2005 ). Similarity and proximity contribute to feelings of familiarity ( Berscheid, 2010 ). Also, caregiving and empathy are positively related to emotional interdependence ( Hatfield et al., 1994 ).

Trust is crucial for love ( Esch and Stefano, 2005 ) and it plays an important role in relationship intimacy and caregiving ( Rempel and Holmes, 1985 ; Wilson et al., 1998 ; Salazar, 2015 ), as well as attachment ( Rodriguez et al., 2015 ; Bidmon, 2017 ). Familiarity is a sine qua non for trust ( Luhmann, 1979 ), and trust is key to relationship satisfaction ( Simpson, 2007 ; Fitzpatrick and Lafontaine, 2017 ).

Respect is cross-cultural and universal ( Frei and Shaver, 2002 ; Hendrick et al., 2010 ) and has been described as fundamental in love ( Hendrick et al., 2011 ). It plays a cardinal role in interpersonal relations at all levels ( Hendrick et al., 2010 ). Indeed, it is essential in relationship commitment and satisfaction ( Hendrick and Hendrick, 2006 ) and relationship intimacy and attachment ( Alper, 2004 ; Hendrick et al., 2011 ).

Synergetic Interactions of the Four Factors

Connection and attraction.

Similarity, proximity, and familiarity are all important in connection because they promote attachment and a sense of oneness in a relationship ( Sullivan et al., 2011 ; Beckes et al., 2013 ). Research indicates that proximity ( Batool and Malik, 2010 ) and familiarity positively influence attraction ( Norton et al., 2015 ) and several lines of evidence suggests that people are attracted to those similar to themselves ( Sykes et al., 1976 ; Wetzel and Insko, 1982 ; Montoya et al., 2008 ; Batool and Malik, 2010 ; Collisson and Howell, 2014 ). Also, attraction mediates similarity and familiarity ( Moreland and Zajonc, 1982 ; Elbedweihy et al., 2016 ).

Respect and Trust

Evidence suggests that respect promotes trust ( Ali et al., 2012 ).

Connection, Respect, Trust, and Attraction

Trust affects attraction ( Singh et al., 2015 ). Trust and respect can mediate attitude similarity and promote attraction ( Singh et al., 2016 ).

So, although these factors can operate independently, evidence suggests that the weakening of one factor could negatively affect the others and the status of love. Similarly, the strengthening of one factor positively modulates the others and the status of love.

Relationships are dynamic and change as events and conditions in the environment change ( Berscheid, 2010 ). Love is associated with causal conditions that respond to these changes favorably or negatively ( Berscheid, 2010 ). In other words, as conditions change, and these factors become present, love is achieved and if they die, it fades. Figure 1 below explains how love grows and dies. Point C in the figure explains the variations in the intensity or levels of love and this variation is influenced by the strength of each factor. The stronger the presence of all factors, the higher the intensity and the lower, the weaker the intensity of love. The concept of non-love is similar to the “non-love” described in Sternberg’s triangular theory of love in which all components of love are absent ( Sternberg, 1986 ).

Figure 1. Description: (A) Presence of love (all factors are present). (B) Absence of love (state of non-love or state where all factors are latent or dormant). (C) Different levels of love due to variations in the four factors. (D) Movement from non-love toward love (developmental stage: at least one but not all four factors are present). (E) Movement away from love toward non-love (decline stage: at least one or more of the four factors are absent).

Application of the Quadruple Framework on Romantic, Brand and Parental Love

Romantic, parental and brand love have been chosen to demonstrate the role of these factors and their interactions in love because there is significant existing literature on them. However, they can be applied to understand love in all its forms.

Romantic Love

Attraction and romantic love.

Attraction involves both physical and personality traits ( Braxton-Davis, 2010 ; Karandashev and Fata, 2014 ). To this end, attraction could be subdivided into sexual or material and non-sexual or non-material attraction. Sexual or material attraction includes physical attributes such as beauty, aesthetics, appeal, wealth, etc. In contrast, non-sexual or non-material attraction includes characteristics such as personality, social status, power, humor, intelligence, character, confidence, temperament, honesty, good quality, kindness, integrity, etc. Both types of attraction are not mutually exclusive.

Romantic love has been described as a advanced form of human attraction system ( Fisher et al., 2005 ) and it fits with the passion component of Sternberg’s triangular theory of love which he described as the quickest to recruit ( Sternberg, 1986 ). Indeed, research indicates that physical attractiveness and sensual feelings are essential in romantic love and dating ( Brislin and Lewis, 1968 ; Regan and Berscheid, 1999 ; Luo and Zhang, 2009 ; Braxton-Davis, 2010 ; Ha et al., 2010 ; Guéguen and Lamy, 2012 ) and sexual attraction often provides the motivational spark that kickstarts a romantic relationship ( Gillath et al., 2008 ). Behavioral data suggest that love and sex drive follow complementary pathways in the brain ( Seshadri, 2016 ). Indeed, the neuroendocrine system for sexual attraction and attachment appears to work synergistically motivating individuals to both prefer a specific mating partner and to form an attachment to that partner ( Seshadri, 2016 ). Sex promotes the activity of hormones involved in love including arginine vasopressin in the ventral pallidum, oxytocin in the nucleus accumbens and stimulates dopamine release which consequently motivates preference for a partner and strengthens attachment or pair-bonding ( Seshadri, 2016 ).

Also, romantic love is associated with non-material attraction. Research indicates that many people are attracted to their romantic partner because of personality traits like generosity, kindness, warmth, humor, helpfulness, openness to new ideas ( Giles, 2015 , pp. 168–169). Findings from a research study on preferences in human mate selection indicate that personality traits such as kindness/considerate and understanding, exciting, and intelligent are strongly preferred in a potential mate ( Buss and Barnes, 1986 ). Indeed, character and physical attractiveness have been found to contribute jointly and significantly to romantic attraction ( McKelvie and Matthews, 1976 ).

Attraction is key to commitment in a romantic relationship ( Rusbult, 1980 ), indicating that without attraction a romantic relationship could lose its luster. Also, romantic attraction is weakened or declines as the reason for its presence declines or deteriorates. If attraction is sexual or due to material characteristics, then aging or any accident that compromises physical beauty would result in its decline ( Braxton-Davis, 2010 ). Loss of fortune or social status could also weaken attraction and increase tension in a relationship. Indeed, tensions about money increase marital conflicts ( Papp et al., 2009 ; Dew and Dakin, 2011 ) and predicted subsequent divorce ( Amato and Rogers, 1997 ).

Connection and Romantic Love

Connection or resonance fits with the intimacy, and commitment components of Sternberg’s triangular theory of love ( Sternberg, 1986 ). Connection in romantic love involves intimacy, friendship or companionship and caregiving and it is strengthened by novelty, proximity, communication, positive shared experiences, familiarity, and similarity. It is what creates a sense of oneness between romantic partners and it is expressed in the form of proximity seeking and maintenance, concern, and compassion ( Neto, 2012 ). Evidence suggests that deeper levels of emotional involvement or attachment increase commitment and cognitive interdependence or tendency to think about the relationship in a pluralistic manner, as reflected in the use of plural pronouns to describe oneself, romantic partner and relationship ( Agnew et al., 1998 ).

Research indicates that both sexual attraction and friendship are necessary for romantic love ( Meyers and Berscheid, 1997 ; Gillath et al., 2008 ; Berscheid, 2010 ), indicating that connection which is essential for companionship plays a key role in romantic love. A study on college students by Hendrick and Hendrick (1993) found that a significant number of the students described their romantic partner as their closest friend ( Hendrick and Hendrick, 1993 ), reinforcing the importance of friendship or companionship in romantic love.

Similarity along the lines of values, goals, religion, nationality, career, culture, socioeconomic status, ethnicity, language, etc. is essential in liking and friendship in romantic love ( Berscheid and Reis, 1998 ). Research indicates that a partner who shared similar values and interests were more likely to experience stronger love ( Jin et al., 2017 ). Indeed, the more satisfied individuals were with their friendships the more similar they perceived their friends to be to themselves ( Morry, 2005 ). Also, similarity influences perceptions of familiarity ( Moreland and Zajonc, 1982 ), and familiarity plays a role in the formation of attachment and connectedness because it signals safety and security ( Bowlby, 1977 ). Moreover, similarity and familiarity affect caregiving. Sprecher and Fehr (2005) , found compassion or caregiving were lower for strangers, and greatest for dating and marital relationships, indicating that similarity and familiarity enhance intimacy and positively influences caregiving ( Sprecher and Fehr, 2005 ).

Proximity through increased exposure is known to promote liking ( Saegert et al., 1973 ), familiarity and emotional connectedness ( Sternberg, 1986 ; Berscheid, 2010 ). Exposure through fun times and direct and frequent communication is essential to maintaining and strengthening attachment and connectedness ( Sternberg and Grajek, 1984 ). In Sternberg’s triangular theory, effective communication is described as essential and affects the intimacy component of a relationship ( Sternberg, 1986 ). Indeed, intimacy grows from a combination of mutual self-disclosure and interactions mediated by positive partner responsiveness ( Laurenceau et al., 1998 , 2005 ; Manne et al., 2004 ), indicating that positive feedback and fun times together strengthens connection.

Also, sexual activity is an important component of the reward system that reinforces emotional attachment ( Seshadri, 2016 ), indicating that sexual activity may increase emotional connectedness and intimacy. Over time in most relationships, predictability grows, and sexual satisfaction becomes readily available. This weakens the erotic and emotional experience associated with romantic love ( Berscheid, 2010 ). Research shows that a reduction in novelty due to the monotony of being with the same person for a long period is the reason for this decline in sexual attraction ( Freud and Rieff, 1997 , p. 57; Sprecher et al., 2006 , p. 467). According to Sternberg (1986) , the worst enemy of the intimacy component of love is stagnation. He explained that too much predictability can erode the level of intimacy in a close relationship ( Sternberg, 1986 ). So, novelty is essential to maintaining sexual attraction and strengthening connection in romantic love.

Jealousy and separation distress which are key features of romantic love ( Fisher et al., 2002b ), are actions to maintain and protect the emotional union and are expressions of a strong connection. Research has found a significant correlation between anxiety and love ( Hatfield et al., 1989 ) and a positive link between romantic love and jealousy in stable relationships ( Mathes and Severa, 1981 ; Aune and Comstock, 1991 ; Attridge, 2013 ; Gomillion et al., 2014 ). Indeed, individuals who feel strong romantic love tend to be more jealous or sensitive to threats to their relationship ( Orosz et al., 2015 ).

Connection in romantic love is weakened by distance, a dearth of communication, unsatisfactory sexual activity, divergences or dissimilarity of values and interests, monotony and too much predictability.

Trust and Romantic Love

Trust is the belief that a partner is, and will remain, reliable or dependable ( Cook, 2003 ). Trust in romantic love fits with the intimacy, and commitment components of Sternberg’s triangular theory of love which includes being able to count on the loved one in times of need, mutual understanding with the loved one, sharing of one’s self and one’s possessions with the loved one and maintaining the relationship ( Sternberg, 1986 ).

It has been proposed that love activates specific regions in the reward system which results in a reduction in emotional judgment and fear ( Seshadri, 2016 ). This reduced fear or trust has been identified as one of the most important characteristics of a romantic relationship and essential to fidelity, commitment, monogamy, emotional vulnerability, and intimacy ( Laborde et al., 2014 ). Indeed, trust can deepen intimacy, increase commitment and increase mutual monogamy, and make a person lower their guards in the belief that they are safe from harm ( Larzelere and Huston, 1980 ; Bauman and Berman, 2005 ). People with high trust in romantic relationships tend to expect that their partner will act in their interest causing them to prioritize relationship dependence over making themselves invulnerable from harm or self-protection ( Luchies et al., 2013 ). In contrast, people with low trust in their partner tend to be unsure about whether their partner will act in their interests and prioritize insulating themselves from harm over relationship dependence ( Luchies et al., 2013 ).

Trust takes time to grow into a romantic relationship. Indeed, people in a relationship come to trust their partners when they see that their partner’s action and behavior moves the relationship forward or acts in the interest of the relationship and not themself ( Wieselquist et al., 1999 ). Research indicates that trust is associated with mutual self-disclosure ( Larzelere and Huston, 1980 ), and positive partner responsiveness which are both essential to the experience of friendship and intimacy in romantic relationships ( Larzelere and Huston, 1980 ; Reis and Shaver, 1988 ; Laurenceau et al., 1998 ).

Also, trust influences caregiving and compassion. Evidence suggests that compassion is positively related to trust ( Salazar, 2015 ). Mutual communal responsiveness or caregiving in relationships in which partners attend to one another’s needs and welfare is done because they are confident that the other will do the same when or if their own needs arise ( Clark and Monin, 2006 ). Repeated acts of communal responsiveness given with no expectation of payback provide a partner with a sense of security and trust and increase the likelihood that they will be communally responsive if or when the need arises ( Clark and Monin, 2006 ), and contributes to a sense of love in romantic relationships ( Berscheid, 2010 ).

Loss or weakening of trust could spell the end of romantic love. Indeed, mistrust corrupts intimacy and often indicates that a relationship has ended or near its end ( LaFollette and Graham, 1986 ) and it makes mutual monogamy, and commitment difficult to achieve in a romantic relationship ( Towner et al., 2015 ). A study on individuals who had fallen out of romantic love with their spouse found that loss of trust and intimacy was part of the reason for the dissolution of love ( Sailor, 2013 ).

Respect and Romantic Love

Multiple lines of evidence suggest that respect is expected in both friendships and romantic relationships ( Gaines, 1994 , 1996 ). In romantic love, it entails consideration, admiration, high regard, and value for the loved one as a part of one’s life ( Sternberg and Grajek, 1984 ; Hendrick et al., 2011 ).

Gottman (1999) , found that the basis for a stable and satisfactory marital relationship is friendship filled with fondness and admiration ( Gottman, 1999 ). Respect is considered one of the most important things married couples want from their partner ( Gottman, 1994 ). Grote and Frieze (1994) , found that respect correlates with companionate or friendship love ( Grote and Frieze, 1994 ), indicating that respect is essential to intimacy and relationship satisfaction. Also, respect is positively correlated with passion, altruism, self-disclosure, and relationship overall satisfaction ( Frei and Shaver, 2002 ; Hendrick and Hendrick, 2006 ). It is associated with the tendency to overlook a partner’s negative behavior or respond with pro-relationship actions or compassion to their shortcomings ( Rusbult et al., 1998 ; Gottman, 1999 ).

Absence or a lack of respect could spell the end of romantic love. Research indicates that there is an expectation of mutual respect in friendship and most relationships and people reacted negatively when this expectation is violated ( Hendrick et al., 2011 ), indicating that a lack of respect could negatively affect commitment and attraction. Indeed, denial of respect is an important negative behavior in friendships and most relationships ( Gaines, 1994 , 1996 ) and a lack of respect is a violation of what it means to love one ‘s partner in a close romantic relationship ( Hendrick et al., 2011 ). Gottman (1993 , 1994) identified contempt, criticism, defensiveness, and stonewalling as four of the relationally destructive behavior and he labeled them as “the four horsemen of the apocalypse.”

Romantic love summary

Romantic love involves the interactions and synergistic interplay between respect, connection, trust, and attraction. All four must be present in love. Any event that results in the loss of any of these factors could cause romantic love to gradually decline and unless effort is made to replenish it, it will eventually fade or collapse. Romantic love is dynamic and requires significant investment from both partners to keep it alive.

Parental Love

Attraction and parental love.

Attraction plays an essential role in parental love and it could be material or non-material. Material attraction involves the child’s health, gender, accomplishments or success, and attractiveness. In contrast, non-material attraction includes traits such as intelligence, character, and other personality traits.

Evidence suggests that culture influences gender preference with attraction greater for sons in most cases ( Cronk, 1993 ). Indeed, mothers and fathers have been found to favor the more intelligent and more ambitious/industrious child ( Lauricella, 2009 ). Also, parental perception that investment in a child will cost more than the benefits to be gained from taking care of the child might influence negative behavior toward the child. Indeed, multiple lines of evidence suggest that parental unemployment increases the rates of child maltreatment and abuse ( Steinberg et al., 1981 ; Lindo et al., 2013 ). Research indicates that teen mothers who have poor social support reported greater unhappiness, were at greater risk for child abuse and often employed the use of physical punishment toward their child ( Haskett et al., 1994 ; de Paúl and Domenech, 2000 ).

Also, several studies have suggested that parents tended to favor healthy children ( Mann, 1992 ; Barratt et al., 1996 ; Hagen, 1999 ). However, when resources are plentiful, parents tend to invest equally in less healthy or high-risk children ( Beaulieu and Bugental, 2008 ), because they have abundant resources to go around without compromising the reproductive value of healthy children ( Lauricella, 2009 ).

Connection and Parental Love

Connection creates a sense of oneness between parent and child and involves caregiving, intimacy, and attachment. It is influenced by proximity, positive and unique shared experiences, and similarity along virtually every dimension between parent and child.

Proximity, and similarity increases attachment and intimacy between parent and child. Research shows that parents are perceived as favoring genetically related children ( Salmon et al., 2012 ), and evidence suggests that paternal resemblance predicted paternal favoritism ( Lauricella, 2009 ). Parental proximity and similarity to a biological child are unique because it is based on genes and blood. In contrast, intimacy between a parent and an adopted child is based solely on shared experiences and proximity and takes time to grow and on many occasions may not develop ( Hooks, 1990 ; Hughes, 1999 ).

Dissimilarities or discrepancy in values, attitudes, etc., can create problems between children and parents and can have a profound effect on their relationship. Indeed, evidence suggests that the rebel child tended to be less close to the parents ( Rohde et al., 2003 ). Research has found that adolescents who are less religious than their parents tend to experience lower-quality relationships with their parents which results in higher rates of both internalizing and externalizing symptoms ( Kim-Spoon et al., 2012 ). When parents and family members were very religious, and a child comes out as an atheist, relationship quality could suffer in the form of rejection, anger, despair, or an inability to relate to one another ( Zimmerman et al., 2015 ). A study of lesbian, gay, and bisexual youngsters, for patterns of disclosure of sexual orientation to families, found that those who had disclosed reported verbal and physical abuse by parents and family members ( D’Augelli et al., 1998 ). Honor killing of female children which have been reported in Pakistan and some parts of the Middle East because of deviation from traditional gender roles or crossing of social boundaries that are deemed as taboo in their culture ( Lindsey and Sarah, 2010 ), is another example of the negative effects of the discrepancy in values between parents and child.

Unique shared experiences between parent and child could increase connection. Bank (1988) observed that the development of favoritism seems to require that the “child’s conception or birth be unusual or stressful,” ( Bank, 1988 ). Evidence suggests that parents most favored child tended to be last-born child and this is linked to their unique position, vulnerability and neediness ( Rohde et al., 2003 ). Also, proximity, positive experiences and time spent together increases connection and intimacy. Research indicates that parents tend to give more love and support to the grown child they were historically closest to and got along with ( Siennick, 2013 ). A study of primiparous women found that mothers with greater contact with their infants were more reluctant to leave them with someone else, and engaged more intimately with their child ( Klaus et al., 1972 ).

Divorce could create distance between a parent and child, weakening connection and intimacy. Indeed, one of the outcomes of divorce is the lessening of contact between divorced non-custodial fathers and their children ( Appleby and Palkovitz, 2007 ), and this can reduce intimacy ( Guttmann and Rosenberg, 2003 ).

Also, parental separation distress, worry, and concern for their child’s welfare, academic performance, and future are expressions of connection and a lack thereof is a sign of poor connection. Indeed, the levels of concern and worry expressed between children and their parents influenced their perceptions of the relationship quality ( Hay et al., 2007 ).

Trust and Parental Love

Trust is essential to parental attachment, intimacy, and caregiving. When there is mistrust, attachment and intimacy between a parent and their child are disrupted or unable to blossom. In Africa and many parts of the world, there have been reports of children being condemned and abandoned by their parents simply because they are tagged as witches with mysterious evil powers ( Tedam, 2014 ; Bartholomew, 2015 ; Briggs and Whittaker, 2018 ). The tag of “witchcraft” stirs up fear and anger, causing the child to be perceived as a deadly threat which inevitably damages attachment, intimacy and eliminates the need for caregiving.

Research has found that firstborn children were most likely to be chosen as those to whom mothers would turn when facing personal problems or crises ( Suitor and Pillemer, 2007 ). This tendency may be linked to trust. Moreover, evidence suggests that the rebel child tended to be less close to the parents ( Rohde et al., 2003 ). In other words, the more obedient, and reliable child is likely to gain the confidence and intimacy of the parents. In contrast, the disobedient and unreliable child is excluded or kept at a distance. Also, trust and poor connection could influence inheritance and disinheritance decisions. Indeed, estrangement, alienation and disaffection of a parent toward a child could result in disinheritance ( Batts, 1990 ; Brashier, 1994 , 1996 ; Foster, 2001 ; Arroyo et al., 2016 ).

Respect and Parental Love

Respect in parental love entails treating the child with consideration and regard. This consideration and regard for the child are essential to intimacy, caregiving and attachment. Indeed, respect is foundational to a harmonious relationship between parent and child ( Dixon et al., 2008 ). Evidence suggests that humans possess an innate behavioral system that leads them to form an attachment to a familiar person who provides care, comfort, and protection ( Harlow, 1958 ; Bowlby, 1989 ). Repeated acts of caregiving contribute to a sense of love in all types of relationships ( Berscheid, 2010 ), reinforcing the role of parental caregiving in fostering intimacy and attachment with the child.

Taking care of an infant’s needs, and making sure they are safe and well, all fall under consideration and regard for the child. Child abuse and neglect ( Tedam, 2014 ; Bartholomew, 2015 ; Briggs and Whittaker, 2018 ), is a display of a lack of consideration for the child’s need.

Also, respect in parental love involves admiration. Research has found that fathers treated more ambitious/industrious sons with high regard, and both parents favored the more intelligent and more ambitious/industrious daughters ( Lauricella, 2009 ) indicating that a child that engages in activities or behavior that is highly regarded by their parents may gain favor with their parents, strengthening intimacy and vice versa.

Parental love summary

Parental love involves the interactions and synergistic interplay between respect, connection, trust, and attraction. Any event that results in the loss of any of these factors could cause parental love to gradually decline. In many cases, the behavior and actions of a child significantly influence parental love.

Brand love has been defined as the level of passionate emotional attachment a satisfied or happy consumer has for a brand and evidence suggests it is very similar to interpersonal love ( Russo et al., 2011 ).

Attraction and Brand Love

Attraction plays an essential role in brand love. Material attraction for a brand includes attributes like superior design, quality, and aesthetics, price, benefits, etc. Non-material attraction involves social status symbol, brand personality, uniqueness, distinctiveness, user experience, image, etc. evidence suggests that when talking about loved brands, people often talk passionately about the brand’s many attractive qualities such as its exceptional performance, good-looking design, value for money, and other positive attributes ( Fournier, 1998 ; Whang et al., 2004 ; Carroll and Ahuvia, 2006 ; Batra et al., 2012 ). Research on brand love has found that brand attractive attributes such as prestige or uniqueness influence brand passion which affects relevant factors such as purchase intention ( Bauer et al., 2007 ).

Also, brand attraction influences brand loyalty, and commitment. Indeed, research indicates that brand benefits influences brand loyalty or commitment ( Huang et al., 2016 ). Brand personality (image, distinctiveness, and self-expressive value) is strongly associated with brand identification and loyalty ( Kim et al., 2001 ; Elbedweihy et al., 2016 ).

Connection and Brand Love

Connection is essential to brand love. It involves brand attachment, commitment, and intimacy and it is strengthened by brand identification, image, familiarity or awareness, proximity, length or frequency of usage and similarity or congruences along virtually every dimension including values, lifestyle, goals, etc. between brand and customer. Brand awareness which means brand familiarity has been described as essential for people to identify with a brand ( Pascual and Académico, 2015 ), and it indirectly affects current purchases ( Esch et al., 2006 ).

Also, brand identification promotes a sense of oneness between a brand and a customer strengthening commitment and it is driven by brand self-similarity, brand prestige and brand distinctiveness ( Stokburger-Sauer et al., 2008 ). Indeed, brand identification contributes to the development of brand love and brand loyalty ( Alnawas and Altarifi, 2016 ) and brand image and identification influence loyalty and positive word of mouth ( Carroll and Ahuvia, 2006 ; Batra et al., 2012 ; Anggraeni and Rachmanita, 2015 ). Brand identity, values and lifestyle similarities to those of the customer appear to have a strong and significant relationship with brand love ( Batra et al., 2012 ; Rauschnabel and Ahuvia, 2014 ; Alnawas and Altarifi, 2016 ; Elbedweihy et al., 2016 ). Findings from research suggest that customer-to-customer similarity and sense of community drive consumer brand identification, loyalty, and engagement ( Bergkvist and Bech-Larsen, 2010 ; Elbedweihy et al., 2016 ).

Moreover, proximity and interaction play a role in brand love. Indeed, the duration of the relationship between a customer and a brand is essential in brand love ( Albert et al., 2007 ). Fournier (1998) , discussed interdependence which involved frequent brand interactions as necessary for a strong brand relationship ( Fournier, 1998 ). Similarly, Batra et al. (2012) found that having a long-term relationship, positive emotional connection and frequent interactions with a brand was an important aspect of brand love ( Batra et al., 2012 ). Indeed, shared experiences and history between a person and a brand can increase their emotional attachment, make the brand to become an important part of the person’s identity narrative and increases their loyalty to the brand ( Thomson et al., 2005 ; Pedeliento et al., 2016 ).

Just like romantic love, concern and worry and proximity seeking, or maintenance are an expression of emotional connectedness to the brand. Indeed, anticipated separation distress has been described as a core element of brand love ( Batra et al., 2012 ), and consumers are likely to feel strong desires to maintain proximity with their loved objects, even feeling “separation distress” when they are distanced from them ( Thomson et al., 2005 ; Park et al., 2010 ).

Also, novelty through continued innovation is vital to maintaining and strengthening both attraction and connection. According to the Harvard business review, the relationship between brand and consumer go through “ruts” and to “keep the spark” alive, innovation and news are essential ( Halloran, 2014 ). Research indicates that innovation plays a role in brand equity and it impacts brand identification or resonance ( Sinha, 2017 ).

Lack of brand familiarity or awareness, poor or negative user experience, a dearth of innovation and increased dissimilarities in values and lifestyles between brand and consumer can all weaken brand connection.

Trust and Brand Love

Trust is essential to brand attachment, intimacy, and commitment. It involves confidence and reliability, or dependability of the brand and it is influenced by brand image, familiarity, values, user experience, and quality. Indeed, brand trust directly influences brand love ( Turgut and Gultekin, 2015 ; Meisenzahl, 2017 ) and a strong relationship exists between brand love and brand trust and identification ( Albert and Merunka, 2013 ). Evidence suggests that brand familiarity influences brand trust ( Ha and Perks, 2005 ) and brand trust and experience, positively influence brand attachment ( Erciş et al., 2012 ; Chinomona, 2013 ; Chinomona and Maziriri, 2017 ).

Also, brand trust affects brand purchase, loyalty, and commitment. Evidence suggests that a strong relationship exists between brand love and brand trust, brand commitment, positive word of mouth, and willingness to pay a higher price for the brand ( Albert and Merunka, 2013 ). Research indicates that brand trust positively affects brand loyalty ( Setyawan and Kussudiyarsana, 2015 ), directly influences brand purchase intentions ( Yasin and Shamim, 2013 ) and positively influences current and future purchases ( Erciş et al., 2012 ). Indeed, more than any other factor, brand trust has been identified as essential for future purchases of a brand ( Esch et al., 2006 ). It is essential in determining purchase loyalty and attitudinal loyalty and it plays a role in brand market share ( Chaudhuri and Holbrook, 2001 ). Brand trust affects both affective and continuance commitment and affective commitment influences repurchase intention and loyalty ( Erciş et al., 2012 ).

Brand quality is essential to brand trust and love. Indeed, Fournier (1998) , discussed the role of brand quality in brand love and highlighted the role of trust in relationship satisfaction and strength ( Fournier, 1998 ). Also, brand trust has been found to positively affect resistance to negative information and repurchase intention ( Turgut and Gultekin, 2015 ).

Brand trust is weakened by poor user experience, brand quality, brand image, and a lack of brand familiarity.

Respect and Brand Love

Brand respect is essential in brand love and plays an important role in brand attachment, intimacy, and commitment. It is influenced by brand identification, values, image, experience, and quality. Brand respect is displayed by the customer in the form of high regard, admiration for the brand, brand loyalty and consideration or tolerance of negative information. Indeed, brand familiarity positively affects brand respect ( Zhou, 2017 ), indicating that brand familiarity increases regard for a brand. Evidence suggests that brand image positively influences brand respect and love ( Cho, 2011 ), indicating that brand image modulates a customer’s regard and admiration for a brand.

Brand respect influences brand commitment and loyalty. Indeed, a strong relationship has been found between brand respect and brand loyalty ( Cho, 2011 ) and brand admiration results in greater brand loyalty, stronger brand advocacy, and higher brand equity ( Park et al., 2016 ). Brand respect affects the behavioral outcomes of brand love such as affective commitment, and willingness to pay a price premium ( Garg et al., 2016 ; Park et al., 2016 ).

Also, evidence suggests that customers’ admiration or high regard for a brand contributes to why they tend to ignore negative information about the brand ( Elbedweihy et al., 2016 ). Fournier (1998) , included respect as one of the components of brand partner quality. This means that respect is one of the factors that reflects the consumer’s evaluation of the brand’s performance ( Fournier, 1998 ).

A lack of respect could negatively influence the relationship between a brand and a customer. Indeed, people react negatively when the expectation of respect is violated ( Hendrick et al., 2011 ) and a violation of expectation between brand and customer has been found to contribute to brand hate ( Zarantonello et al., 2016 ).

Brand love summary

Brand love involves the interactions and synergistic interplay between respect, connection, trust, and attraction. Any event that results in the loss of any of these factors could cause brand love to gradually decline and unless effort is made to replenish it, it will eventually fade or collapse. Brand love is dynamic and requires significant investment from the brand to keep it alive.

Strengths and Advances Made by the Quadruple Theory

The quadruple theory builds on many of the strengths of previous theories of love and it applies a temporal approach that has been proposed as the best way to understand love ( Berscheid, 2010 ). It goes further than previous theories for several reasons. Firstly, it could potentially be applied to any form of love although, only brand, romantic and parental love were discussed in this paper due to the paucity of scholarly articles on other forms of love. One of the reasons current love scales and approaches have been unable to be applied in all forms of love ( Hendrick and Hendrick, 1989 ; Whitley, 1993 ; Sternberg, 1997 ; Masuda, 2003 ; Graham and Christiansen, 2009 ), is because they capture only a part of the ACC model, unlike the quadruple framework which fully captures it.

Unlike previous theories, the quadruple theory’s application of the complex factor of connection/resonance gives it an edge in furthering our understanding of love. Proximity, positive shared experience, familiarity, and similarity are vital to connection and connection has the most profound influence on all the other factors.

Also, the dynamism and variation of these factors provide a fresh way to understand love from its development to collapse. As Figure 1 shows, love tends to take time to mature in a relationship and can die as these factors rise and decline. Figure 1 shows that variations in the presence of these factors represent different levels of love. Love in any relationship is influenced by the events in the environment it is embedded, and it responds favorably or negatively to these changes. Indeed, people get sick, old, lose their finances, travel in search of greener pastures creating distance, develop new interests different from their partner’s and all these influences the presence and absence of love. One brand becomes more innovative, improves its product quality and users experience over another and people gradually love it more than the one they previously loved. In other words, love is very dynamic and may be divided into high, moderate and low. Another point highlighted in Figure 1 is that the absence of one factor represents the absence of love and only the presence of all factors represents the presence of love. Indeed, the decline of a factor can be replenished in response to changes in the environment causing the reestablishment of love. Trust could decline but attraction and respect remain and over time trust could be replenished.

This dynamic understanding of love implies that it can be nurtured and sustained. As an example, for a brand to be loved and to maintain that love, it must make products that are attractive (appealing). It must be able to connect to its target customers by reaching out through adverts to achieve familiarity and it must ensure that its values, goals, actions are consistently similar to those of its customer base. Also, it must ensure its services and products and actions promote and maintain trust with its customers. It must respect (value) its customer’s interests and ensure that its services and products continue to receive the admiration of its customers. Table 2 describes how brand love can be nurtured and preserved.

Table 2. Brand love can be nurtured and maintained.

Using this framework, a love scale or algorithm could be developed to ascertain the presence or absence of love in any relationship. Such a scale must effectively capture these four factors and must consider the type of love being calculated in its approach. As an example, in trying to create a scale for romantic love, sexual attraction, and activity may be important for attraction and connection (depending on the age of the partners) but would be unnecessary in the calculation of brand or parental love.

Major Challenges for the Theory

One of the biggest challenges the theory faces is the lack of psychometric data to prove many of its claims. Most of its arguments are based on decades of psychological data, but its lack of psychometric data weakens the theory significantly. Also, the entire premise of the theory is based on the ACC model, which has not been validated as essential or foundational to understanding love. Perhaps, something else needs to be added to the model that the theory may have missed. The argument that the quadruple theory captures the ACC model better than previous theories on love is an argument that has not been validated, and it remains to be seen if this is true. Also, the argument that it can be applied to all forms of love apart from the three discussed remains to be tested and verified.

Gaps currently exist in our understanding of love and evidences from the existing literature show that a framework that can be applied to all forms of love is needed. The quadruple theory hopes to be that framework. It is likely to broaden our understanding of the complex nature of love. It could make love less complex by making it something that can be cultivated or nurtured, regulated and preserved. Future research should consider the modulatory roles of peptides, neurotransmitters, and hormones on these factors and their influence on love as well as the integrated parts of the brain that modulates all these factors and how they work synergistically in different stages of love.

It is important to note that love is universal and applies to people of all cultures, races, ethnicities, religion and sexual orientations. Indeed, romantic love as described by the quadruple theory applies equally to heterosexual relationships and to the relationships of people in the LGTBQ community.

In conclusion, culture has a monumental influence on what people feel, think, and how they behave toward other people and things in their environment ( Karandashev, 2015 ; Ching Hei and David, 2018 ). So, it can be considered a modulating factor on the factors discussed and on love.

Author Contributions

The author confirms being the sole contributor of this work and has approved it for publication.

Conflict of Interest

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords : triangular theory of love, Romance, brand love, parental love, maternal love, Meaning of love, Definition of love, am I in love

Citation: Tobore TO (2020) Towards a Comprehensive Theory of Love: The Quadruple Theory. Front. Psychol. 11:862. doi: 10.3389/fpsyg.2020.00862

Received: 20 September 2019; Accepted: 07 April 2020; Published: 19 May 2020.

Reviewed by:

Copyright © 2020 Tobore. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Tobore Onojighofia Tobore, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Psychologily

Sternberg’s Triangular Theory of Love: Explained and Simplified

Love is a complex and multifaceted emotion. In his research, psychologist Robert Sternberg proposed a Triangular Theory of Love that breaks down the components of love into three main elements: intimacy, passion, and commitment. According to this theory, each element plays a crucial role in defining the different types of love that people experience.

The Triangular Theory of Love is an influential concept in psychology, as it provides a comprehensive framework for understanding the various aspects of love. Sternberg’s theory proposes that intimacy involves feelings of closeness and emotional connection between two people, passion involves physical attraction and sexual desire, and commitment consists of the decision to stay with someone and work towards a future together. By breaking down love into these three components, the theory can help us better understand the complex nature of relationships.

The Triangular Theory of Love proposes eight different types of love, each characterized by a unique combination of the three elements. These types include non-love, liking, infatuated, empty, romantic, companionate, fatuous, and consummate love. Each class has distinct features and implications for relationships, making the theory a valuable tool for understanding the complexities of love.

Sternberg’s

Regarding understanding love, Robert Sternberg’s Triangular Theory of Love is a popular framework that has gained widespread acceptance in psychology. This theory proposes that love comprises three primary components: intimacy, passion, and commitment. Each of these components plays a unique role in shaping the nature of a given relationship.

According to Sternberg’s Triangular Theory of Love, the three components of love are as follows:

• Intimacy  refers to the emotional closeness and connectedness that two people share. It involves feelings of warmth, trust, and mutual understanding. Intimacy is crucial for building strong, healthy relationships, as it allows partners to feel safe and secure with one another.
• Passion  refers to the intense physical and emotional attraction that two people share. It involves feelings of desire, excitement, and arousal. Passion is an essential component of love, as it helps to fuel the initial stages of a relationship and keep the spark alive over time.
• Commitment  refers to the decision to stay with one’s partner and work towards a shared future together. It involves feelings of dedication, loyalty, and responsibility. Commitment is critical for building long-lasting, stable relationships, as it provides a sense of security and stability.

Sternberg’s Triangular Theory of Love was first introduced in 1986 in a paper published in the Psychological Review. Since then, it has become one of psychology’s most widely recognized and influential theories of love. The theory has been used to explain various interpersonal relationships, from romantic partnerships to friendships and familial bonds.

While the theory has its critics, many researchers have found it to be a valuable tool for understanding the complex nature of love and relationships. By breaking love down into its parts, Sternberg’s Triangular Theory of Love offers a framework for understanding the different factors contributing to a given relationship’s success or failure.

Components of The Theory

Sternberg’s Triangular Theory of Love suggests that love consists of three components: Intimacy, Passion, and Commitment. Each component plays a unique role in the formation of a loving relationship. In this section, we will discuss each of these components in detail.

Intimacy refers to emotional closeness and connectedness between two individuals. It involves feelings of trust, understanding, and mutual support. Intimacy is characterized by open and honest communication, sharing personal thoughts and feelings, and a sense of comfort and safety in each other’s company.

Intimacy can be expressed in various ways, such as through deep conversations, physical touch, and acts of kindness. Couples with a strong sense of intimacy often feel a deep sense of fulfillment and satisfaction in their relationship.

Passion refers to the romantic and physical attraction between two individuals. It involves feelings of desire, excitement, and sexual attraction. Passion is often characterized by physical touch, sexual intimacy, and romantic gestures.

Passion can be expressed in various ways, such as through kissing, hugging, holding hands, and engaging in sexual activity. Couples with a strong sense of passion often feel deep excitement and attraction towards each other.

Commitment refers to the decision to maintain the love in the long term. It involves feelings of loyalty, dedication, and responsibility towards each other. Commitment is often characterized by a willingness to work through challenges, support each other’s goals, and sacrifice for the relationship.

Commitment can be expressed in various ways, such as through making plans together, supporting each other’s dreams, and making sacrifices for the relationship. Couples with a strong commitment often feel a deep sense of security and stability in their relationship.

Sternberg’s Triangular Theory of Love suggests that love comprises three components: Intimacy, Passion, and Commitment. Each component plays a unique role in forming a loving relationship, and couples with a strong sense of all three components often feel a deep sense of fulfillment and satisfaction.

Types of Love According to Sternberg

Sternberg’s Triangular Theory of Love proposes that love comprises intimacy, passion, and decision/commitment. These three components combine to create eight different types of love. Let’s explore them below.

Nonlove is the absence of all three components of love. A lack of intimacy, passion, and commitment characterizes this relationship. An example of nonlove would be two strangers walking past each other on the street.

Liking is the presence of only one component of love: intimacy. Liking is characterized by closeness and warmth towards someone without passionate or committed feelings. An example of liking would be two coworkers who have a friendly relationship but no romantic interest in each other.

Infatuated Love

Infatuated love is the presence of only one component of love, passion. Infatuated love is characterized by intense desire and excitement without intimacy or commitment. An example of infatuated love would be a crush on someone you just met.

Empty love is the presence of only one component of love, commitment. A commitment to a relationship without intimacy or passion characterizes empty love. An example of empty love is two people who have been married for a long time but no longer have romantic feelings for each other.

Romantic Love

Romantic love is the presence of two components of love, intimacy and passion. Romantic love is characterized by strong emotional and physical attraction towards someone without long-term commitment. An example of romantic love would be a new couple who are deeply in love but have not made any long-term plans together.

Companionate Love

Companionate love is the presence of two components of love, intimacy and commitment. A deep emotional connection and commitment to a long-term relationship without intense passion characterize companionate love. An example of companionate love would be an elderly couple who have been married for decades and have a deep emotional connection but may no longer have a physical relationship.

Fatuous Love

Fatuous love is the presence of two components of love, passion and commitment. Fatuous love is characterized by a whirlwind romance leading to a quick commitment without real emotional intimacy. An example of fatuous love would be a couple who get married after only knowing each other for a short period.

Consummate Love

Consummate love is the presence of all three components of love, intimacy, passion, and commitment. Consummate love is characterized by a deep emotional connection, intense physical attraction, and a long-term commitment to a relationship. An example of consummate love would be a couple who have been together for many years and have a strong emotional and physical connection and a commitment to each other for the long term.

According to Sternberg’s Triangular Theory, understanding the different types of love can help us better understand our relationships and what components of love may be present or absent.

Applications of The Theory

Sternberg’s Triangular Theory of Love has many practical applications in psychology. Here are two significant applications of the theory.

Relationship Counseling

Relationship counseling is one of the most common applications of Sternberg’s Triangular Theory of Love. The theory can help couples understand the nature of their relationship and identify areas that need improvement. For instance, if a couple has a strong sense of intimacy but lacks passion, the theory suggests they may need to improve their physical and romantic connection. Similarly, if a couple has a strong sense of passion but lacks commitment, the theory suggests that the couple may need to work on building a long-term commitment.

The theory can also help counselors identify the root cause of relationship problems. For example, if a couple is experiencing issues with commitment, the counselor may use the theory to explore the underlying factors contributing to the problem. By understanding the nature of the couple’s relationship, the counselor can develop a treatment plan that addresses the couple’s specific needs.

Understanding Personal Relationships

Sternberg’s Triangular Theory of Love can also be used to understand personal relationships. The theory suggests that love comprises intimacy, passion, and commitment. By understanding these components, individuals can gain insight into their relationships and identify areas that need improvement.

For example, suppose an individual has a strong sense of intimacy but lacks passion. In that case, the theory suggests that the individual may need to build a more romantic and physical connection with their partner. Similarly, if an individual has a strong sense of passion but lacks commitment, the theory suggests that the individual may need to work on building a stronger long-term commitment.

Sternberg’s Triangular Theory of Love is a valuable tool for understanding and improving personal relationships. By understanding the nature of love, individuals can develop more fulfilling and satisfying relationships with their partners.

Critiques of The Theory

While Sternberg’s Triangular Theory of Love is widely recognized and influential in psychology, it is not without its critiques. This section will explore some of the criticisms raised against this theory.

One of the main criticisms of the Triangular Theory of Love is that it oversimplifies the complexity of human relationships. While the theory suggests that love can be broken down into three components, many argue that other factors contribute to the experience of love, such as trust, respect, and shared values. Additionally, some argue that the theory needs to account for the different ways people experience love, such as through friendships, familial relationships, or non-romantic partnerships.

Another critique of the Triangular Theory of Love is that it lacks empirical support. While the theory has been widely discussed and debated in academic circles, limited empirical evidence supports its claims. Some studies have attempted to test the theory using Sternberg’s Triangular Love Scale, but the results have been mixed, with some studies finding support for the theory and others finding little to no evidence of its validity.

Finally, some have criticized the Triangular Theory of Love for being too focused on Western cultural norms and values. A Western psychologist developed the theory, which has primarily been studied in Western countries, which raises questions about its applicability to other cultures and societies. Critics argue that the theory may need to accurately capture the experience of love in non-Western cultures, where different values and norms may shape people’s understanding and expression of love.

While the Triangular Theory of Love has contributed significantly to our understanding of love and relationships, it is essential to recognize its limitations and critiques. By acknowledging these critiques, we can continue to refine and improve our experience of what it means to love and be loved.

Frequently Asked Questions

What are the three components of sternberg’s triangular theory of love.

According to Sternberg’s triangular theory of love, there are three components of love: intimacy, passion, and commitment. Intimacy refers to emotional closeness and connectedness, passion refers to romantic and physical attraction, and commitment refers to the decision to maintain the love in the long term.

What are the four stages of Sternberg’s triangular theory of love?

Sternberg’s triangular theory of love includes four stages: liking, infatuation, empty love, and consummate love. Liking involves only intimacy, infatuation involves only passion, empty love involves only commitment, and consummate love involves all three components of love: intimacy, passion, and commitment.

What is empty love?

Empty love is the stage in Sternberg’s triangular theory of love, where only commitment is present. This means that there is no emotional closeness or physical attraction in the relationship.

What is consummate love, according to Sternberg?

Consummate love is the ultimate form of love in Sternberg’s triangular theory of love. It involves all three components of love: intimacy, passion, and commitment. This means that there is emotional closeness, physical attraction, and a long-term commitment in the relationship.

What is the psychology definition of fatuous love?

Fatuous love is a type of love that involves passion and commitment, but lacks intimacy. This means that there is physical attraction and a long-term commitment, but no emotional closeness in the relationship.

Is Sternberg’s triangular theory of love considered accurate?

Sternberg’s triangular theory of love has been widely accepted and studied in the field of psychology. However, some researchers have criticized the theory for oversimplifying the complexity of love and relationships. While it may not be a perfect representation of all types of love, it provides a useful framework for understanding the different components and stages of love.

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• Published: 31 January 2024

A decade of love: mapping the landscape of romantic love research through bibliometric analysis

• Yixue Han 1 ,
• Yulin Luo 1 ,
• Zhuohong Chen 1 ,
• Nan Gao 1 ,
• Yangyang Song 1 &
• Shen Liu 1  

Humanities and Social Sciences Communications volume  11 , Article number:  187 ( 2024 ) Cite this article

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Given the limited availability of bibliometric and visual analysis on the topic of romantic love, the primary objective of the current study is to fill this gap by conducting a comprehensive visual analysis of relevant literature. Through this analysis, the current study aimed to uncover current research trends and identify potential future directions in the field of romantic love. The current study’s search criteria were met by an impressive 6858 publications found in the Web of Science database for the period between 2013 and 2022. A thorough analysis was conducted on the bibliographic visualization of the authors, organizations, countries, references, and keywords. Over time, there has been a remarkable surge in the number of significant publications. Among the authors in the field of romantic love, Emily A. Impett has emerged as the most prolific. The Journal of Social and Personal Relationships is indeed one of the top journals that has published a significant number of articles on the topic of romantic love. During the preceding decade, the University of California System emerged as a prominent producer of publications centered around romantic love, solidifying the United States’ position as a dominant player in this field. In recent times, there has been a significant surge in the popularity of keywords such as “same-sex,” “conflict resolution,” and “social relationships” within academic literature. These topics have experienced a burst of attention, as evidenced by a substantial increase in references and citations. Through the use of visualization maps and analysis of key publications, the current study offers a comprehensive overview of the key concepts and potential avenues for future research in the field of romantic love. Gaining a deep understanding of the complex dynamics and societal implications of romantic love has been instrumental in formulating policies that embody increased compassion and support. As a result, these policies have played a pivotal role in fostering resilient familial ties and contributing to the enduring stability and prosperity of our social fabric.

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Introduction, the development course of romantic love.

Romantic love, as defined by Hatfield and Rapson ( 1987 ) as an intense longing for union with another, has long been recognized as a driving force behind some of humanity’s most remarkable achievements. Studies by Bartels and Zeki ( 2000 ) and the work of Fehr ( 2013 , 2015 ) have further emphasized its profound impact. Previous research has suggested that romantic love has a crucial role in the development and maintenance of romantic relationships. It involves a transition from the significant investment of time and attention in the initial stages to enhanced communication and satisfaction in committed partnerships (Mizrahi et al. 2022 ). However, recent research has shown that in the United States, the divorce rate has consistently remained at historically high levels. According to the Centers for Disease Control and Prevention ( 2017 ), ~40–50% of first marriages end in divorce. In recent times, there has been a trend toward shorter and more prevalent romantic relationships. Alirezanejad ( 2022 ) found that different generations of women have maintained distinct expectations and experiences when it comes to love. Additionally, the significance of commitment in romantic relationships has witnessed a decline. These findings also indicate that there are additional factors at play that influence the dynamics between romantic love and the duration of relationships. The triangular theory of love, being one of the most widely used theories on romantic love, proposes that romantic love consists of three components: intimacy, passion, and an absence of commitment, alongside a willingness to invest resources without expecting reciprocation (Jimenez-Picon et al. 2022 ). The Love Attitude Scale (LAS) developed by Clyde and Susan Hendrick has been a significant contribution in the study of romantic love using psychometric methods. Tobore ( 2020 ) introduced a comprehensive four-fold framework that aims to elucidate the dynamics of how love evolves and diminishes. This framework includes the elements of attraction, empathy or connection, trust, and respect. As a result, the enigmatic and unique nature of romantic love has captivated the attention of scholars from various disciplines, including psychology, biology, sociology, and neuroscience. These scholars have conducted extensive research and investigations into the complexities of romantic love. Thus, the present study conducted a comprehensive and in-depth analysis and discourse on romantic love, spanning multiple research domains. Additionally, the publication emphasized the influence of romantic love on positive emotions as well as its association with various negative behaviors. Furthermore, it underscored the importance of utilizing bibliometric analysis as a valuable approach to study and understand romantic love.

The research directions of romantic love in different disciplines

Psychologists have focused on exploring the relationship between romantic love and negative emotions in individuals with mental illnesses. Lafontaine et al. ( 2020 ) found a correlation between romantic love insecurity, specifically anxiety and avoidance, and the occurrence of intimate partner violence (IPV). This pattern of behavior was shown to undermine relationships and diminish individuals’ sense of security. Moreover, individuals with schizophrenia and other mental health conditions faced significant challenges in building and sustaining healthy interpersonal connections, partly due to the enduring stigma associated with mental illness (Budziszewska et al. 2020 ). Biological researchers have delved into the physiological activities and responses associated with romantic love. Furthermore, biological research has demonstrated that communication plays a crucial role in enhancing romantic relationships by facilitating physiological and behavioral adaptations between partners. For instance, a study by Zeevi et al. ( 2022 ) revealed that men and women in a romantic relationship can enhance their romantic interest in each other by synchronizing their skin electrical activities and modifying their behavior. These findings suggest that the social adaptation of the sympathetic nervous system and motor behavior play a critical role in the romantic attraction between partners. Furthermore, recent biological research conducted by Kerr et al. ( 2022 ) has discovered a correlation between unsuitable adult attachment in romantic relationships and the interpersonal circumplex, which is a component of personality pathology. Furthermore, a sociological study on pair-bonding conducted by Fletcher et al. ( 2015 ) highlighted that romantic love is intricately linked to the evolution and survival of Homo sapiens, making it a biologically significant function with profound evolutionary implications. Neuroscientists have examined the activation of different brain regions that are triggered by romantic love activities. Functional magnetic resonance imaging (fMRI) has emerged as a prominent technique for studying the neurobiological basis of love. Researchers such as Acevedo et al. ( 2020 ) and Chester et al. ( 2021 ) have utilized fMRI to investigate the neural correlates of romantic love and gain insights into the brain mechanisms underlying this complex phenomenon. Neuroscientists have identified specific brain regions associated with love, including the insula and anterior cingulate cortex. These regions are involved in the processing of emotional experiences related to valued objects. A study by Bartels and Zeki ( 2000 ) highlighted the involvement of these brain regions in the experience of romantic love, shedding light on the neural mechanisms underlying the emotional aspects of love. The activation of reward-related areas in the brain, particularly those rich in oxytocin, has been observed in individuals experiencing love. Studies by Acevedo et al. ( 2012 ) and Bartels and Zeki ( 2004 ) have shown that regions associated with reward processing, such as the ventral tegmental area and nucleus accumbens, are involved in the experience of romantic love. Indeed, the involvement of the reward system in love has surpassed expectations. During the initial stages of romantic love, research conducted by Fisher et al. ( 2010 ) has shown that reward-related brain regions, including the bilateral ventral tegmental areas, are activated more strongly compared to the later stages of passion.

The social impact of romantic love

Undoubtedly, falling in love has a profound impact on people’s daily lives, as highlighted by research conducted by Quintard et al. ( 2021 ). Falling in love has been associated with enhanced well-being and has been correlated with fervor, activity, pleasure, and other positive emotions, as noted in research conducted by Langeslag ( 2022 ). However, it is important to acknowledge that the pitfalls of romantic love are often overlooked. Research, such as that conducted by Lonergan et al. ( 2022 ), has found associations between romantic love and criminal activity as well as psychological disorders. Additionally, studies by Aron et al. ( 2005 ), Merritt et al. ( 2022 ) and Li et al. ( 2022 ) have highlighted the presence of unpleasant affective states such as hyperarousal, anxiety, and depression in the context of romantic love. In recent decades, romantic love has undergone significant transformations that have had a substantial impact on both personal and societal life, as emphasized by research conducted by Reis et al. ( 2013 ).

The necessity of bibliometric analysis

Bibliometrics is a field that encompasses the quantitative study of documents, aiming to provide researchers with insights into academic, technological, and scientific advancements (William and Concepción 2001 ). The methodology utilized a range of techniques, including author analysis, concept mapping, clustering, factor analysis, and citation analysis, to investigate historical data and assist scholars in identifying significant trends and emerging directions within their disciplines (Daim et al. 2006 ; Hou et al. 2022 ). The term “bibliometrics” was coined by the distinguished British scientist Allen Richard in 1969, replacing the previously employed term “statistical bibliography.” In recent years, there has been a surging interest in this approach, with a growing number of researchers incorporating it into their work. Bibliometric analysis has been employed in various research domains, including the study of romantic love. These analyses offer valuable insights into the research areas that have been investigated, as well as potential future trends, challenges, and opportunities in the field. To the best of our knowledge, there have been limited previous publications that have specifically analyzed romantic love based on the triangular theory of love development and explored the concept across different disciplines.

In the current study, we utilized state-of-the-art analytical tools, including CiteSpace (6.2.R2), VOSviewer (1.6.18), Microsoft Excel (2019), and Scimago Graphica (1.0.26), in conjunction with the most recent data obtained from the Web of Science (WOS) core collection database. These tools allowed us to conduct a comprehensive bibliometric and visual analysis of publications related to romantic love published in the last decade. By employing these cutting-edge tools and leveraging the extensive data available from WOS, we aimed to gain valuable insights into the research landscape surrounding romantic love during this specific time frame. Our study aimed to achieve several objectives. First, we sought to identify the current research hotspots and trends within the field of romantic love. Second, we aimed to conduct an in-depth examination of visual maps and seminal articles, providing a comprehensive overview of the literature.

Material and methods

Data acquisition and search strategy.

The Web of Science (WOS) platform served as a valuable resource, containing a vast collection of over 9000 significant academic articles. This database stands as one of the oldest and most comprehensive citation index records, encompassing a wide range of disciplines, including social science, engineering technology, biomedicine, arts and humanities, and various other subjects. Since its establishment in 1900, the Web of Science (WOS) has served as a cornerstone of scholarly research and has wielded significant influence within academic circles (Ellegaard and Wallin 2015 ). The quantitative analysis feature of the platform facilitated the acquisition of various types of information related to scholarly publications. This included data on the annual number of papers published, papers published by state or region, popular journals within specific disciplines, frequently utilized publishing houses, and highly downloaded and cited literature. Indeed, references that receive multiple citations play a crucial role in providing a robust foundation for the study of romantic love, as emphasized by Xu et al. ( 2022 ).

The subject matter of romantic love and its interrelation with romantic relationships has a profound impact on the satisfaction and longevity of love between individuals, as highlighted by Zagefka ( 2022 ). Passionate love is a fundamental concept within romantic relationships, as emphasized by Mizrahi et al. ( 2022 ). Sternberg’s triangular theory of love stands as one of the most substantial and frequently referenced frameworks for understanding love, as noted by Sorokowski et al. ( 2021 ). To comprehensively explore the topic, the search strategy incorporated the inclusion of the following elements: The topic could encompass “romantic love,” OR “passionate love,” OR “romantic relationship,” OR “triangular theory of love.”‘ The search was conducted within the Web of Science Core Collection database, which covers the time period from 2013 to 2022. The database indexes the Science Citation Index Expanded (SCI-EXPANDED) and Social Science Citation Index-Expanded (SSCI-EXPANDED). The search was limited to publications written in the English language. To refine the search and focus on specific types of publications, certain categories were excluded from the search results. These excluded categories included early access, book chapters, proceeding papers, data papers, and retracted publications. By excluding these categories, the search aimed to prioritize reviews and articles, which are typically considered primary sources of scholarly information. As a result of these refined search criteria, a total of 6858 relevant items were identified and included in the analysis.

The retrieval strategy employed in this research was designed to maintain the integrity and impartiality of the search process (see Fig. 1 ).

To ensure that the search results were not influenced by daily database updates, all searches were conducted on a single day, specifically on March 26, 2023.

Analysis tool

For bibliometric analysis, the current study utilized a powerful combination of CiteSpace (6.2.R2), VOSviewer (1.6.18), Microsoft Excel (2019), and Scimago Graphica (1.0.26). These state-of-the-art software tools seamlessly integrated insights from scientometrics, information science, computer science, and other related fields to generate highly intuitive and informative visual maps. These maps revealed the development trajectory and structural underpinnings of scientific research. Indeed, each of these four software applications held unique and irreplaceable significance, excelling in specific domains of bibliometric analysis. Excel, for instance, demonstrated unparalleled proficiency in the intuitive transformation of charts. CiteSpace specialized in the clustering of topics and the delineation of the spatio-temporal background of words. VOSviewer played a pivotal role in both displaying and analyzing keywords, leveraging its distinctive capabilities. Lastly, Scimago Graphica contributed significantly to the geographical perspective of statistical analysis, offering insights that were unmatched in their comprehensiveness. Collectively, these tools not only proved indispensable but also brought their individual strengths to the forefront, contributing uniquely to the overall analytical landscape. Indeed, the Excel program was commonly employed to comprehensively analyze key data points such as the number of published papers, frequency of citations, and matched published documents. It was also employed to synthesize all the information for creating intuitive visual representations (Fig. 2 ) to illustrate the trends in the number of publications, citations, and their corresponding fitting functions during different periods. The use of CiteSpace in the current study was focused on highlighting the most salient occurrence burst on a timeline map and detecting the centrality of romantic love studies (Zhang et al. 2022a ). In order to attain a comprehensive understanding of the progress in romantic love research, an evolutionary analysis was undertaken, utilizing CiteSpace’s burst function. Co-occurrence analysis on pertinent keywords is another valuable method used to gain insights into the relationships and patterns among keywords in a specific research domain. Indeed, the analyses conducted, including the evolutionary analysis and co-occurrence analysis, facilitated an examination of the prevailing themes and trends of romantic love across different generations from a chronological perspective. VOSviewer, a powerful visualization tool, was utilized in the current study to portray the borders of romantic love with varying color clusters. It also facilitated the exploration of the co-occurrence of authors, institutions, and keywords associated with romantic love. The circles of various colors and sizes were used to represent the occurrence frequency of distinct cluster words and different keywords, respectively. The examination of keywords in the current study, augmented by chart analysis, delved into a more profound, comprehensive, and scientific level. Scimago Graphica 1.0.18, a tool designed for visualizing international collaboration, proved highly effective in the current study for facilitating the visualization of international collaboration (He et al. 2022 ). By organically combining the atlas and the world map, researchers were able to intuitively observe differences in the number of publications across various countries and the extent of national collaboration between different regions.

The trend exhibited an upward trajectory, with an estimated 938 publications in 2021, compared to 502 publications in 2013. Notably, the annual publication volume in the field of romantic love had reached its peak in 2021, as indicated by the fitted equation. However, it is worth mentioning that there was a slight decrease in publication numbers during specific periods. From 2017 to 2018, the annual publication count declined from 644 to 608. Similarly, from 2019 to 2020, there was a minor decrease from 872 to 861 publications annually. Additionally, there was a slight decline from 2021 to 2022, with the number of publications decreasing from 938 to 817 annually.

In the previous study, a comprehensive range of factors was considered to provide a thorough and scientifically rigorous atlas analysis of romantic love research. These factors included the annual publication rate, citation counts, H-index, impact factor, centrality, and occurrence/citation burst. An increase in the volume of publications can indicate the growth of a field and provide insights into future research directions (Wang 2016 ). While the number of citations a paper receives may not directly measure an author’s academic influence, it can indicate the recognition of the author’s work by peers worldwide. The “H-index” was a tool for evaluating academic influence, where a researcher with an “H-index” of 10 had 10 papers that had been cited at least 10 times (Wang et al. 2021 ). Since its inception in the 1950s, the impact factor has been widely regarded as a prominent index for ranking scientific literature. It has become an emblem of the prestige and significance of journals and authors in determining the relevance of a journal (Oosthuizen and Fenton 2014 ). For the current study, Journal Citation Reports (JCR) were utilized to calculate impact factors (2021). The centrality of research objects can indeed reflect their impact on the entire field, with greater centrality indicating a greater representation of homologous study content within a subject area. In the study conducted by Gao et al. ( 2021 ), betweenness centrality scores were adjusted to the range of [0, 1]. Specifically, if the betweenness centrality score of a main keyword exceeded 0.10, it was considered to indicate the significance of the study target. In the study conducted by Xu et al. ( 2022 ), the concept of a “burst term” was utilized to refer to an unexpected term that emerged in the research, potentially indicating new directions or orientations discovered during the investigation. The Kleinberg burst detection method, which is implemented in the CiteSpace software, was employed to identify these burst terms and highlight them as indicators of frontier research.

Publication outputs

A total of 6858 records met the search criteria. As depicted in Fig. 2 , the number of annual publications in the field of romantic love has shown a consistent upward trend since 2013. This increase is accompanied by a corresponding surge in citation counts, as indicated by the fitted equation. Citation counts in the field of romantic love have also experienced a significant upsurge since 2013, with an approximate 90-fold increase by 2022. Furthermore, based on current trends and fitting curves, the number of studies in this field is expected to continue rising, with an increasing number of researchers focusing on this topic.

Distribution by journals

The current study retrieved a total of 6858 records from 1251 journals, with ~33.79% of the material published by 20 publications that released more than 50 papers in this field. The top ten journals, accounting for 23.78% (92–400) of all papers published, had an average publication count of 134 papers per journal (see Table 1 ). Among them, the Journal of Social and Personal Relationships (400 publications, IF 2021 = 2.681) had the highest number of papers on romantic love research, followed by Personal Relationships (189 publications, IF 2021 = 1.528), and Personality and Individual Differences (185 publications, IF 2021 = 3.950). Notably, the Journal of Personality and Social Psychology was the most influential professional core journal in this field, boasting the highest impact factor (8.460). Both European and American journals have made significant contributions to this field, with the United States and the United Kingdom accounting for 40% and 50% of the top 10 journal publishing countries/regions, respectively. The impact factors of the top 10 most-published journals ranged from 1.528 to 8.460, with an average of 4.070. It is worth noting that publishing romantic love-related articles in high-impact journals remains challenging.

Distribution by authors and research areas

A staggering 15,088 authors contributed to the total number of papers. In Fig. 3 , the collaborative efforts of the writers were illustrated through a network map, where the connections between the nodes signified their collaborative affiliations. Among the top three clusters, the red cluster included authors Joseph P. Allen, Martine Hebert, and Marie-France Lafontaine, who had converged due to their shared research interests in adolescent dating violence and aggression (Cenat et al. 2022 ; Niolon et al. 2015 ). The blue cluster consisted of authors Frank D. Fincham, James K. Monk, and Ashley K. Randall, who had explored the interplay between relationship satisfaction, stress, and relationship maintenance in romantic relationships (Randall and Bodenmann 2017 ; Vennum et al. 2017 ). The yellow cluster included authors Todd K. Shackelford, William J. Chopik, and Justin K. Mogilski, whose work focused on the topic of polygamy (Moors et al. 2019 ; Sela et al. 2017 ). Martine Hebert, Todd K. Shackelford, Frank D. Fincham, and Emily A. Impett emerged as the cooperative network’s central nodes, underscoring their crucial role in advancing research on romantic love.

The authors’ cooperative network was partitioned into eight distinct clusters.

Table 2 provided a rundown of the most productive authors, with their published works ranging from 28 to 74 publications, averaging 41. The H-index, a yardstick for measuring academic influence, was employed to assess their impact. Notably, Emily A. Impett emerged as the dominant force within the cohort of scholars dedicated to the study of romantic love, having authored the most papers among the group (74 publications, H-index = 38). Additionally, Nickola C. Overall (42 publications, H-index = 19) and Amy Muise (60 publications, H-index = 30) also featured prominently as leading contributors to the field.

Table 3 and Fig. 4 displayed the number of publications in different fields of study related to the topic of romantic love. Notably, publications in the fields of biology, neuroscience, and economics were also included in Table 3 . The humanities were increasingly collaborating on romantic love research. Furthermore, the topic of romantic love was gaining popularity in the fields of psychology and sociology.

The field of psychology, including psychology and psychiatry, was significantly ahead. The field of sociology encompassed various topics in the social sciences, including sociology and social work.

Distribution by country and institution

A total of 6858 publications had been published and disseminated to 104 countries and regions worldwide. In the country analysis, Scimago Graphica had been used to explore the geographic collaboration network of participating nations. The participants of the current study were drawn from 104 different countries spanning Asia, Africa, Europe, North America, and South America, with Europe exhibiting the highest level of overall engagement, underscoring the global trend toward collaboration. The United States and the United Kingdom had demonstrated the greatest degree of cooperation. Notably, China, South Africa, Spain, Italy, France, and other countries with high cooperation densities had formed the most significant multi-center cooperation network in this field (see Fig. 5 ). Figure 6 illustrated international collaboration.

By leveraging Scimago Graphica, it was possible to merge geographical perspectives with national publications and collaborative relationships, providing an intuitive and scientific method to illuminate the various conditions of countries involved in the research on romantic love.

The largest blue cluster was comprised of the United States, China, Switzerland, Turkey, and Norway, demonstrating collaboration across the Americas, Europe, and East Asia.

Table 4 outlined the specifics of the top ten countries in the landscape of romantic love research. The United States topped the list with 4092 publications, followed by Canada with 802 publications, and the United Kingdom with 540 publications. It is noteworthy that the majority of publications were disseminated from high-income countries, aligning with the overall prosperity of those nations. Most papers were disseminated in high-income countries. This trend might have stemmed from the overarching principles governing scientific inquiry, or it could be attributed to authors in these nations having the freedom to engage in research spanning areas not necessarily centered on economic growth. However, within the realm of general well-being, this emerges as a pertinent concern. Primarily, high-income countries historically boasted more affluent reservoirs of research resources, encompassing financial backing, cutting-edge equipment, and a pool of adept talent. This affluence empowered researchers in these nations to embark on a diverse array of investigations, spanning domains intricately tied to economic growth and extending to those delving into broader realms such as general well-being and social development. The discernible divergence in resource allocation likely contributed to the disproportionate prevalence of publications in high-income countries. Secondarily, the scrutiny of whether the romantic love research domain intricately correlates with economic growth warrants profound contemplation. At times, the merit of research doesn’t solely reside in its potential to spur short-term economic growth but extends to its impact on the overarching well-being and sustainable evolution of society. High-income countries, historically oriented toward prioritizing protracted social well-being, manifested a proclivity to endorse research that, while not directly contributing to economic growth, played an indispensable role in the comprehensive development of society. Institutional collaboration was vividly portrayed in Fig. 7 , which consisted of six clusters. A total of 3328 institutions contributed to the 6858 articles on romantic love. Of the top 10 organizations, universities occupied the top spot (as indicated in Table 5 ), with the State University System of Florida (246 publications), the University System of Ohio (248 publications), and the University of California System (365 publications) leading the pack. Notably, nine out of the top 10 institutions hailed from the United States, which was a testament to the country’s exceptional research prowess in this field.

The red cluster denoted collaboration among Florida State University, University of Michigan, University of Washington, and Indiana University; the green cluster represented Ohio State University, University of Basel, and Nanyang Technological University; while the blue cluster embodied York University, the University of Toronto, Northwestern University, and Carleton University. Northwestern University, Florida State University, the University of Minnesota, and the University of Toronto were the major nodes in the cooperative network.

Analysis of references

Reference analysis played a critical role in bibliometric research, as the references with the highest citation bursts formed the foundation of knowledge at the forefront of research (Fitzpatrick 2005 ). In Fig. 8 , the current study presented the most relevant references on romantic love, which had experienced a surge in citations over the past decade. By the end of 2022, Mikulincer and Shaver’s ( 2016 ) articles had seen a significant increase in their citation counts, with the highest spike (14.35) observed in 2016, followed by Wincentak et al.’s ( 2017 ) studies (9.9). These two studies had been widely cited over the years and accurately captured the latest trends in romantic love research.

These references were represented by red and green bars, indicating their frequent and less frequent citation, respectively.

Mikulincer and Shaver’s ( 2016 ) delved into the causes and methods for measuring individual differences in adult attachment, as well as how to modify attachment styles, using several empirical studies. Additionally, they explored the cutting-edge genetics, neurological, and hormonal substrates of attachment, expanding the impact model’s depiction of how the attachment system functioned. In the study, Wincentak et al. ( 2017 ) discussed the prevalence of dating violence among adolescents of different genders using a meta-analysis method, while also examining the potential regulatory effects of age, demographics, and measurement. Research has shown that in adolescent dating violence, the crime rate of women was significantly lower than that of men. Based on the analysis of these articles, current research trends in romantic love included adult attachment and the examination of adolescents’ irrational beliefs about love and the resulting adverse consequences, such as dating violence.

Analysis of keywords

Keyword burst refers to keywords that have shown a sharp increase in frequency over time, enabling the assessment of the current study focus in this area and reflecting the development pattern of future research. The current study extracted the burst terms of various years in the area of romantic love to obtain the burst terms of various years in the area of romantic love (see Fig. 9 ). As we’ve seen, the field had a diverse range of research interests. By the end of 2022, the three words with the highest peak were “same-sex” (2020–2022), “conflict resolution” (2020–2022), and “social relationships” (2020–2022):

Same-sex: in a society that valued heterosexual relationships, same-sex relationships were often met with shame and stigma, leading to additional pressures uniquely linked to their sexual orientation and partnership (Feinstein et al. 2018 ; Rostosky and Riggle 2017 ). Moreover, the online conduct of gay individuals has been demonstrated to have significant implications for their sexual risk behaviors and emotional well-being in romantic relationships (Zhang et al. 2022b ). The development of effective dual interventions has been shown to enhance the health and well-being of same-sex couples and their families. These interventions should also educate parents about the potential negative effects of heteronormative assumptions and attitudes on their children’s positive adolescent development (Pearson and Wilkinson 2013 ).

Conflict resolution: previous research has shown the irony that a person’s favorite individual, such as their romantic partner, is often the very person with whom they engage in destructive behavior during conflicts, making this destructive response one of the most challenging issues in relationships (Alonso-Ferres et al. 2021 ). As a result, it was critical to effectively resolve conflicts in a constructive manner. The emergence of computer-mediated communication (CMC) as a novel conflict resolution approach prompted researchers to explore this matter. Ultimately, they discovered that there were no differences in pain, anger, and conflict resolution levels between face-to-face and CMC discussions (Pollmann et al. 2020 ). Another study focused on neural activity during conflict resolution, revealing that mediation could enhance conflict resolution and was linked to increased activity in the nucleus accumbens, a crucial area of the brain’s reward circuit (Rafi et al. 2020 ). The finding emphasizes the importance of identifying neural mechanisms that could enhance conflict resolution and improve relationship outcomes. By exploring various conflict resolution approaches and associated neural mechanisms, researchers can facilitate a deeper understanding of how to successfully resolve conflicts and enhance relationship satisfaction.

Social relationships: long-term relationships are vital to the mental health of both humans and animals. Positive emotions and experiences, such as romantic or platonic love, play a significant role in the establishment and maintenance of social bonds. With this in mind, researchers integrated brain imaging studies on emotions characterized by social connections to investigate whether and how humans and animals experience social emotions and influences similarly in the context of social relationships (Zablocki-Thomas et al. 2022 ). An ecological and cross-cutting perspective study found that black Americans viewed their partner’s interactions regarding discrimination as an opportunity for their romantic partner to offer support, as revealed in semi-structured interviews (Rice 2023 ). Furthermore, as romantic relationships represent one of the most unique types of social connections, researchers utilized functional magnetic resonance imaging (fMRI) scanning techniques to explore the neurobiological mechanisms of romantic relationships (Eckstein et al. 2023 ), offering valuable insight for the preservation and maintenance of social relationships and interactions.

Over the last 10 years, the most popular keywords were “same-sex” (11.07), “dating relationships” (9.22), and “HIV” (9.05), indicating high demand for these topics in recent years. The keywords with the longest blasting times were “dating relationships” (2014–2017) and “delinquency” (2014–2017). The phrases that were still trending in 2022 were hotspots.

Figure 10 illustrated the relationship between keywords. The connection strength between two nodes was a quantitative measure of their relationship. The most frequently used keyword, “romantic relationship,” was represented by the largest node in Fig. 10 (see Table 6 ). The “romantic relationship” (2036) node had thicker lines than “attachment” (766), “gender” (728), “satisfaction” (664), “behavior” (529), “marriage” (508), “commitment” (419), “adolescents” (417), “associations” (395), and “intimate partner relationship” (336). The nodes had a minimum link strength of 150. The close connections between “romantic relationship” and “marriage,” “commitment,” and “intimate partnership” demonstrated the importance of stable, long-term relationships in maintaining romantic love (Fu et al. 2012 ).

The connection strength between two nodes was a quantitative measure of their relationship. The total link strength of a node was the sum of its link strengths relative to all other nodes (Liao et al. 2018).

Keywords are essential in identifying the central themes and prospective avenues of a publication. By examining the co-occurrence of keywords, one can discern the current trajectory of research and development in a specific field (Zhang et al. 2022c ). In the present investigation, a total of 16,148 keywords were extracted from 6858 articles related to romantic love, with 10,571 being used only once, accounting for 65.46% of the total keywords. Through keyword co-occurrence analysis, six distinct color-coded clusters were identified, comprising attachment, gender, romantic relationships, personality, communication, and dynamics. The red cluster, attachment, delved into the complex relationships among commitment, fulfillment, companionship, and attachment insecurity. To address the diminished satisfaction in partner relationships caused by attachment insecurity, promoting healthy dualistic coping strategies (DCS) was recommended (Peloquin et al. 2022 ). The green cluster, gender, focused on the issues of dating violence victimization experienced by young individuals of different genders, with sexual minorities being particularly vulnerable to bullying (Cosma et al. 2022 ). The blue cluster, romantic connections, primarily examined the link between depressive symptoms and violent intimate partner relationships. Recent studies showed that dating violence and peer victimization were prevalent among young individuals (Smith et al. 2021 ) and that dating aggression was associated with both internalized and externalized psychopathology in young couples (Lantagne and Furman 2021 ). Additionally, the misuse of internet dating may lead to depression (Toplu-Demirtas et al. 2020 ). Apart from the six clusters mentioned, there was a noticeable trend toward integrating research with neuroimaging technology, which might lead to the emergence of new clusters in the realm of romantic love. The interconnectedness of attachment, gender, and romantic relationships was evident in the strong theoretical foundation and widespread attention these clusters received, whereas the clusters of personality, communication, and dynamics were more peripherally related. Due to their significance, future research on romantic love will continue to explore topics such as intimate partner violence, teenage dating violence victimization, attachment insecurity, and sexual abuse, with a focus on the three interconnected clusters of attachment, gender, and romantic relationships. In traditional notions, our understanding of romantic love had primarily consisted of terms such as romantic relationships and intimate commitments. However, practical issues such as misperceptions about love and a lack of regard for partners have gradually shifted the subject matter of research pertaining to romantic love toward dating violence. The research trajectory demonstrates a shift in the focus of romantic love research from a more idealized perspective toward a more realistic one. Finally, Fig. 11 displayed a keyword timeline graph that depicted when the most prevalent keywords first appeared and their evolving importance over time.

This keyword timeline graph was depicted when the most prevalent keywords first appeared and their evolving importance over time.

The current study used advanced bibliometrics and literature data visualization techniques with CiteSpace, VOSviewer, and Web of Science to examine the growth of research publications in the field of romantic love, as well as the main research nations, journals, and emerging trends. The thorough review provided insight into the present status of development and research in this field, while also clarifying the historical path of scholarship and providing clear guidance for future research. Using bibliometric methods, the study investigated romantic love research from 2013 to 2022. The results showed a steady increase in publications on this topic, with a slight decrease noted in 2019, likely due to the detrimental impact of the COVID-19 pandemic on academic research. However, the analysis of current trends indicates a projected increase in research output on romantic love in the coming years.

Romantic love has been a global phenomenon, with Europe and the United States leading in widespread participation and clear concentration. Among the top 10 countries producing research in this field, the United States led with 4092 publications between 2013 and 2022. China, ranking fourth in terms of publications, emerged as the most prolific developing nation (328). However, compared to the United States, China lagged behind in publications and international collaboration. Therefore, China needs to expand its research efforts in this area and broaden its international partnerships. The top ten research institutions, mainly universities, played a vital role in advancing this field. Notably, nine out of ten of these institutions were located in the United States, further highlighting the preeminent position of American academic institutions in this area of study.

In the current study, we have discovered noteworthy findings regarding notable authors in the field of romantic love. The research studies have primarily focused on four distinct perspectives: the Limerence Theory, the Rate of Change in Intimacy Model, the Self-Expansion Model, and the Triangular Theory of Love. These perspectives have proposed four possible sources of romantic passion and assessed empirical evidence for and against each. Among the authors, Emily A. Impett has emerged as the most prolific author (Carswell and Impett 2021 ). Frank D. Fincham, who has the highest H-index, has conducted extensive research on the interplay between mindfulness and idiosyncratic mindfulness in romantic relationships. Notably, his research on adolescent intimate partner violence has received the most citations (Cui et al. 2013 ; Frank and Ross 2017 ; Kimmes et al. 2018 ). Furthermore, we found that an author’s centrality and citation frequency did not always correlate with their number of publications, indicating that various factors had contributed to an author’s academic influence (Zhang et al. 2022a ).

The term “burst term” refers to a term that unexpectedly appears in research and may indicate new directions or a novel perspective derived from research (Xu et al. 2022 ). According to Fig. 8 , the following references experienced a citation burst by the end of 2022: (1) Mikulincer and Shaver ( 2016 ) delved into the causes and measures of individual differences in adult attachment, explored the modifiability of attachment styles, and unveiled cutting-edge research in genetics, neurology, and hormones associated with attachment. They also extended the impact model’s depiction of the attachment system’s operation. (2) Wincentak et al. ( 2017 ) conducted a meta-analysis to investigate the prevalence of dating violence among adolescents of various genders, while also examining the potential impact of age, demographic factors, and measurement methods. Their findings suggested that the rate of perpetration of dating violence was significantly higher among male adolescents than female adolescents. In other words, male adolescents were more likely to engage in dating violence than their female counterparts. This gender difference in dating violence rates highlighted the need for targeted prevention and intervention efforts to address this issue among young people.

CiteSpace displayed keywords in bursts, as shown in Fig. 9 . These data were significant for reference in cutting-edge prediction research. The terms “same-sex,” “conflict resolution,” and “social relationships” might be used frequently in the coming years, indicating potential areas of focus within the domain of romantic love:

Same-sex: same-sex relationships faced unique pressures and stigma in a society that largely valued heterosexual partnerships, leading to feelings of shame and additional stressors based on sexual orientation (Feinstein et al. 2018 ; Rostosky and Riggle 2017 ). Notably, studies have revealed that the online behavior of gay individuals could significantly impact their emotional well-being and sexual risk behaviors within their romantic relationships (Zhang et al. 2022b ). To improve the health and well-being of same-sex couples and their families, effective dual interventions have been developed, including educating parents about the potential harm caused by heteronormative assumptions and attitudes on their children’s adolescent development (Pearson and Wilkinson 2013 ).

Conflict resolution: prior research has revealed the paradox that a person’s beloved partner, such as their significant other, is often the individual with whom they engage in harmful behavior during conflicts. The negative reaction could be one of the most challenging issues in a relationship (Alonso-Ferres et al. 2021 ). Therefore, it is imperative to resolve conflicts in a successful manner. Computer-mediated communication (CMC) has emerged as a novel approach to conflict resolution, and researchers have investigated this matter, concluding that there are no disparities in the levels of pain, anger, and conflict resolution between face-to-face and CMC discussions (Pollmann et al. 2020 ). Another study explored the neural mechanisms during conflict resolution, and researchers discovered that mediation could improve conflict resolution and was linked to elevated activity in the nucleus accumbens, a crucial area in the brain’s reward circuit (Rafi et al. 2020 ).

Social relationships: long-term relationships play a critical role in maintaining the mental health of both humans and animals. Positive emotions and emotional experiences, such as romantic or platonic love, are intricately linked to the formation and sustenance of social bonds. To gain insights into how social emotions manifest in both humans and animals, researchers integrated brain imaging studies of emotions associated with social connections (Zablocki-Thomas et al. 2022 ). From an ecological and cross-cutting perspective, another study found that Black Americans viewed their partner’s interactions around discrimination as an opportunity for their romantic partner to provide support, as revealed in semi-structured interviews (Rice 2023 ). Furthermore, given the unique nature of romantic relationships in social interactions, researchers used functional magnetic resonance imaging (fMRI) techniques to investigate the neurobiological mechanisms of such relationships (Eckstein et al. 2023 ), which could serve as a reference for the preservation and cultivation of social relationships.

To our knowledge, our study represented a novel application of quantitative bibliometric tools such as CiteSpace and VOSviewer to analyze the literature on romantic love over the past decade. While our analysis yielded intriguing insights into the research landscape of this field, our study was not without limitations. First and foremost, our sample was limited to articles and reviews available in a single database, and thus, may not have been fully representative of the entire research landscape on this topic. Second, the current study restricted our data collection to English-language publications, and future studies may benefit from including publications in other languages to ensure a more comprehensive analysis. Additionally, including different types of publications, such as conference papers and working papers, might have provided further insights into recent advancements in the field. Furthermore, it could be acknowledged that the analysis in the current study could be expanded to consider the contributions of other scholars and institutions in the field, beyond those captured by our data set. Finally, while the bibliometric tools used in our analysis were objective, our interpretation of the results remained subjective and may have been subject to varying interpretations.

Concluding remarks

Research significance and future development.

The present study’s comprehensive analysis of the literature on romantic love, as well as its reporting of research findings across diverse domains over the past decade, offered a solid groundwork for future research and potential worldwide applications. From 2013 to 2022, a staggering 6858 articles and reviews on romantic love were published globally, indicating a bright future for this field of inquiry. In terms of research potency, the United States led the pack, with the University of California System accounting for the majority of publications in the area of romantic love, and Emily A. Impett ranking as the most prolific contributor. The Journal of Social and Personal Relationships had published the most articles on romantic love research, while the most recent trends in romantic love-related keywords included “same-sex,” “conflict resolution,” and “social relationships.” The current research was predominantly centered around intimate relationships, evolutionary psychology, sexual orientation, and symptoms of depression. The trends elucidated by these findings underscore the holistic and interdisciplinary nature of romantic love within the realms of psychology, sociology, biology, and neuroscience. Subsequent investigations into romantic love hold the promise of a more profound amalgamation of methodologies derived from psychology and neuroscience, thereby illuminating the physiological underpinnings of love and emotional experiences. This prospect entails a meticulous exploration of brain activity, probing how intricate psychological processes intertwine with biology to forge the intricacies of romantic relationships. Furthermore, romantic love research stands poised to cultivate seamless integration and interdisciplinary cooperation across a spectrum of fields in the future, yielding profound ramifications.

Method limitation

The current study, which utilized tools such as CiteSpace and Vosviewer for a quantitative analysis of the literature on romantic love over the past 10 years, is the first of its kind to our knowledge. Our investigation, though producing intriguing results through bibliometric analysis and visualization of related articles, is not without its limitations. Firstly, the samples utilized were limited to a single database (WOS), which may not encompass all relevant publications on the subject. Secondly, the scope of our data collection was limited to articles and reviews in English only, leaving out potential information from other types of publications such as working papers and conference papers. In future studies, a broader consideration of different languages should also be given. Additionally, the neural mechanism and physiological function of romantic love remain an under-researched area with limited empirical evidence to support ongoing controversy.

Data availability

Original data for the current study are available via this link: https://rec.ustc.edu.cn/share/0d874150-b039-11ee-be97-f5a41b2eeb6e .

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This research was supported by the Starting Fund for Scientific Research of High-Level Talents at Anhui Agricultural University (rc432206) and the Outstanding Youth Program of Philosophy and Social Sciences in Anhui Province (2022AH030089) to SL.

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Han, Y., Luo, Y., Chen, Z. et al. A decade of love: mapping the landscape of romantic love research through bibliometric analysis. Humanit Soc Sci Commun 11 , 187 (2024). https://doi.org/10.1057/s41599-024-02665-7

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Proximate and Ultimate Perspectives on Romantic Love

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Romantic love is a phenomenon of immense interest to the general public as well as to scholars in several disciplines. It is known to be present in almost all human societies and has been studied from a number of perspectives. In this integrative review, we bring together what is known about romantic love using Tinbergen’s “four questions” framework originating from evolutionary biology. Under the first question, related to mechanisms, we show that it is caused by social, psychological mate choice, genetic, neural, and endocrine mechanisms. The mechanisms regulating psychopathology, cognitive biases, and animal models provide further insights into the mechanisms that regulate romantic love. Under the second question, related to development, we show that romantic love exists across the human lifespan in both sexes. We summarize what is known about its development and the internal and external factors that influence it. We consider cross-cultural perspectives and raise the issue of evolutionary mismatch. Under the third question, related to function, we discuss the fitness-relevant benefits and costs of romantic love with reference to mate choice, courtship, sex, and pair-bonding. We outline three possible selective pressures and contend that romantic love is a suite of adaptions and by-products. Under the fourth question, related to phylogeny, we summarize theories of romantic love’s evolutionary history and show that romantic love probably evolved in concert with pair-bonds in our recent ancestors. We describe the mammalian antecedents to romantic love and the contribution of genes and culture to the expression of modern romantic love. We advance four potential scenarios for the evolution of romantic love. We conclude by summarizing what Tinbergen’s four questions tell us, highlighting outstanding questions as avenues of potential future research, and suggesting a novel ethologically informed working definition to accommodate the multi-faceted understanding of romantic love advanced in this review.

Introduction

Romantic love is a complex suite of adaptations and by-products that serves a range of functions related to reproduction ( Fletcher et al., 2015 ; Buss, 2019 ). It often occurs early in a romantic relationship but can lead to long-term mating. It is a universal or near-universal ( Jankowiak and Fischer, 1992 ; Gottschall and Nordlund, 2006 ; Jankowiak and Paladino, 2008 ; Fletcher et al., 2015 ; Buss, 2019 ; Sorokowski et al., 2020 ) and is characterized by a range of cognitive, emotional, behavioral, social, genetic, neural, and endocrine activity. It occurs across the lifespan in both sexes. Romantic love serves a variety of functions that vary according to life-stage and duration, including mate choice, courtship, sex, and pair-bonding. Its evolutionary history is probably coupled with the emergence of pair-bonds relatively recently in human evolutionary history.

Romantic love has received attention from scholars in diverse fields, including neurobiology, endocrinology, psychology, and anthropology. Our review aims to synthesize multiple threads of knowledge into a more well-rounded perspective on romantic love. To accomplish this, we do the following: First, we lay out our analytical framework based on Tinbergen’s (1963) “four questions” for explaining a biological phenomenon. Second, using this framework as an organizing tool, we summarize what is known about the social mechanisms, psychological mate choice mechanisms, genetics, neurobiology, endocrinology, development across the lifetime of an individual, fitness-relevant functions, and evolutionary history of romantic love. Finally, we conclude by summarizing what Tinbergen’s four questions tell us, identifying areas for future research, and providing a new ethologically informed working definition of romantic love.

Analytical Framework

Much work has been done to examine romantic love as a biological characteristic. Numerous reviews have described the neurobiology and endocrinology of romantic love (e.g., Fisher, 2004 , 2006 ; Zeki, 2007 ; Hatfield and Rapson, 2009 ; Reynaud et al., 2010 ; Cacioppo et al., 2012b ; de Boer et al., 2012 ; Diamond and Dickenson, 2012 ; Dunbar, 2012 ; Tarlaci, 2012 ; Xu et al., 2015 ; Fisher et al., 2016 ; Zou et al., 2016 ; Tomlinson et al., 2018 ; Walum and Young, 2018 ; Cacioppo, 2019 ). Two meta-analyses ( Ortigue et al., 2010 ; Cacioppo et al., 2012a ) considered fMRI studies of romantic love. There have been some accounts of romantic love or love from an evolutionary perspective (e.g., Hendrick and Hendrick, 1991 ; Fisher, 1995 , 2016 ; Fisher et al., 2006 , 2016 ; Kenrick, 2006 ; Lieberman and Hatfield, 2006 ; Schmitt, 2006 ; Fletcher et al., 2015 ; Sorokowski et al., 2017 ; Buss, 2019 ).

No one, however, has addressed the full spectrum of approaches used in biology to provide a comprehensive account of romantic love. We fill this gap by framing our review of romantic love around Tinbergen’s (1963) “four questions” for explaining biological traits. It was developed in the context of trying to provide a holistic, integrative understanding of animal behavior, and is an extension of earlier explanatory frameworks, including Mayr’s (1961) distinction between proximate and ultimate explanations in biology ( Bateson and Laland, 2013 ). It includes two proximate explanations, mechanistic and ontogenetic, and two ultimate (evolutionary) explanations, functional and phylogenetic. To illustrate the use of this framework, we refer to elements of Zeifman’s (2001) analysis of infant crying as a biological trait using this framework. An outline of our use of this framework is presented in Table 1 .

Summary of romantic love using Tinbergen’s (1963) framework.

Proximate explanations focus on the workings of biological and social systems and their components, both on a short-term (mechanistic) and longer-term (ontogenetic) basis ( Tinbergen, 1963 ; Zeifman, 2001 ). Mechanistic explanations attempt to answer questions about how behavior is produced by an organism. It is about the immediate causation of the behavior. A baby’s cry, under this class of explanation, might be viewed as an expression of emotion regulated by the limbic system. In our analysis, we ask: “What are the mechanisms that cause romantic love?” Ontogenetic explanations attempt to answer questions about how the behavior develops over the life course. A baby’s cry, thus, might be viewed as a vocalization that changes in frequency and context over the first year of life, and then across the rest of childhood. In our analysis, we ask: “How does romantic love develop over the lifetime of an individual?”

Ultimate explanations focus on the application of evolutionary logic to understand behavior, both on a short-term (functional) and long-term (phylogenetic) basis ( Tinbergen, 1963 ; Zeifman, 2001 ). Functional explanations attempt to answer questions about the fitness consequences of behavior and how it functions as an adaptation. A baby’s cry, thus, might be viewed as an adaptation that enhances offspring survival by eliciting care or providing information about its state. As the fitness consequences may be negative as well, it might focus on both benefits and costs. For instance, the cry may decrease survival by attracting predators or depleting scarce energy reserves. In our analysis, we ask: “What are the fitness-relevant functions of romantic love?” Phylogenetic explanations attempt to answer questions about the evolutionary history of a behavior and the mechanisms that produce it. A baby’s cry, thus, might be understood from the perspective of whether similar behaviors are present in closely related species. In our analysis, we ask: “What is the evolutionary history of romantic love?”

Tinbergen’s (1963) framework has been a useful tool for organizing research and theory on behavior and other biological traits across all major kingdoms of life, from plants (e.g., Satake, 2018 ) to humans (e.g., Winterhalder and Smith, 1992 ; Zeifman, 2001 ; Stephen et al., 2017 ; Luoto et al., 2019 ). It allows us to build holistic explanations of biological phenomena by examining complementary, but often non-mutually exclusive, categories of explanation ( Bateson and Laland, 2013 ). We believe that this approach to understanding romantic love will clarify the usefulness and interdependence of the various aspects of the biology of romantic love without falling into the pitfalls of posing explanations for the phenomena that are in opposition rather than complementary ( Nesse, 2013 ).

Definitions

There are a number of definitions and descriptions of romantic love. These definitions and descriptions have different names for romantic love, but all are attempting to define the same construct. We present, here, four definitions or descriptions of romantic love that continue to have relevance to contemporary research.

Walster and Walster (1978) were among the first to scientifically define romantic love. They gave it the name “passionate love” and their definition has been revised several times (e.g., Hatfield and Walster, 1985 ; Hatfield and Rapson, 1993 ). A definition of passionate love is:

A state of intense longing for union with another. Passionate love is a complex functional whole including appraisals or appreciations, subjective feelings, expressions, patterned physiological processes, action tendencies, and instrumental behaviors. Reciprocated love (union with the other) is associated with fulfillment and ecstasy; unrequited love (separation) with emptiness, anxiety, or despair ( Hatfield and Rapson, 1993 , p. 5).

Hendrick and Hendrick (1986) propose a description of romantic love in the context of describing six different “love styles” ( Lee, 1976 ). They label it “eros.” It too has undergone some changes. A recent version of the description is:

Strong physical attraction, emotional intensity, a preferred physical appearance, and a sense of inevitability of the relationship define the central core of eros. Eros can “strike” suddenly in a revolution of feeling and thinking ( Hendrick and Hendrick, 2019 , p. 244).

Sternberg (1986) provides a description of romantic love based on three components of love in close relationships: intimacy, passion and commitment. He calls it “romantic love” and describes it as such:

This kind of love derives from a combination of the intimacy and passion components of love. In essence, it is liking with an added element, namely, the arousal brought about by physical attraction and its concomitants. According to this view, then, romantic lovers are not only drawn physically to each other but are also bonded emotionally ( Sternberg, 1986 , p. 124).

A more recent definition of romantic love informed by evolutionary theory has been proposed by Fletcher et al. (2015) . Rather than providing a discrete series of sentences, they propose a working definition of “romantic love” that is explained with reference to some of the psychological research on romantic love and by summarizing five distinct features of romantic love. These features are:

• (1) Romantic love is a powerful commitment device, composed of passion, intimacy, and caregiving;
• (2) Romantic love is universal and is associated with pair-bonding across cultures;
• (3) Romantic love automatically suppresses effort and attention given to alternative partners;
• (4) Romantic love has distinct emotional, behavioral, hormonal, and neuropsychological features; and
• (5) Successful pair-bonding predicts better health and survival across cultures for both adults and offspring ( Fletcher et al., 2015 , p. 22).

Despite these attempts to define and describe romantic love, no single term or definition has been universally adopted in the literature. The psychological literature often uses the terms “romantic love,” “love,” and “passionate love” (e.g., Sternberg and Sternberg, 2019 ). Seminal work called it “limerence” ( Tennov, 1979 ). The biological literature generally uses the term “romantic love” and has investigated “early stage intense romantic love” (e.g., Xu et al., 2011 ), “long-term intense romantic love” (e.g., Acevedo et al., 2012 ), or being “in love” (e.g., Marazziti and Canale, 2004 ). In this review, what we term “romantic love” encompasses all of these definitions, descriptions, and terms. Romantic love contrasts with “companionate love,” which is felt less intensely, often follows a period of romantic love ( Hatfield and Walster, 1985 ), and merges feelings of intimacy and commitment ( Sternberg, 1986 ).

Psychological Characteristics

Hatfield and Sprecher (1986) theoretically developed the Passionate Love Scale to assess the cognitive, emotional, and behavioral components of romantic love among people who are in a relationship. There are other ways of measuring romantic love ( Hatfield et al., 2012 ), and some, such as Sternberg’s Triangular Love Scale ( Sternberg, 1997 ; Sumter et al., 2013 ) or the Love Attitudes Scale ( Hendrick and Hendrick, 1986 ; Hendrick et al., 1998 ), measure the same constructs ( Masuda, 2003 ; Graham, 2011 ). The Passionate Love Scale is only valid in people who are in a romantic relationship with their loved one. Regardless, the Passionate Love Scale provides a particularly useful account of some of the psychological characteristics of romantic love. It has been used widely in research investigating romantic love in relationships ( Feybesse and Hatfield, 2019 ).

Cognitive components of romantic love include intrusive thinking or preoccupation with the partner, idealization of the other in the relationship, and desire to know the other and to be known. Emotional components include attraction to the other, especially sexual attraction, negative feelings when things go awry, longing for reciprocity, desire for complete union, and physiological arousal. Behavioral components include actions toward determining the other’s feelings, studying the other person, service to the other, and maintaining physical closeness ( Hatfield and Sprecher, 1986 ).

Romantic love shares a number of physiological and psychological characteristics with addiction. “[T]hey focus on their beloved (salience); and they yearn for their beloved (craving). They feel a “rush” of exhilaration when seeing or thinking about him or her (euphoria/intoxication). As their relationship builds, the lover experiences the common signs of drug withdrawal, too, including protest, crying spells, lethargy, anxiety, insomnia, or hypersomnia, loss of appetite or binge eating, irritability and chronic loneliness.” ( Fisher et al., 2016 , p. 2) A number of reviews have highlighted the behavioral and neurobiological similarities between addiction and romantic love (e.g., Reynaud et al., 2010 ; Fisher et al., 2016 ; Zou et al., 2016 ).

There is evidence that romantic love is associated with increased hypomanic symptoms (elevated mood, Brand et al., 2007 ; Bajoghli et al., 2011 , 2013 , 2014 , 2017 ; Brand et al., 2015 ), a change (increase or decrease) in depression symptoms ( Stoessel et al., 2011 ; Bajoghli et al., 2013 , 2014 , 2017 ; Price et al., 2016 ; Verhallen et al., 2019 ; Kuula et al., 2020 ), and increased state anxiety ( Hatfield et al., 1989 ; Wang and Nguyen, 1995 ; Bajoghli et al., 2013 , 2014 , 2017 ; Brand et al., 2015 ; Kuula et al., 2020 ). See Supplementary Table 1 for information about studies investigating hypomania, depression, and anxiety symptoms in people experiencing romantic love. Romantic love is also characterized by cognitive biases which resemble “positive illusions,” which are a tendency to perceive one’s relationship and one’s loved one in a positive light or bias ( Song et al., 2019 ).

Proximate Perspectives

When applied to romantic love, the first of Tinbergen’s (1963) four questions asks: “What are the mechanisms that cause romantic love?” This can be answered with reference to social mechanisms, psychological mate choice mechanisms, genetics, neurobiology, and endocrinology ( Zeifman, 2001 ; Bateson and Laland, 2013 ). Research into the social mechanisms and genetics of romantic love are in their infancy, but there is substantial theory on psychological mate choice mechanisms and ample research has been undertaken into the neural and endocrine activity associated with romantic love. Additional insights can be garnered from the neurobiology and endocrinology of psychopathology, cognitive biases, and animal models.

Social Mechanisms

Some precursors to romantic love (others discussed below) that act strongly as social mechanisms that cause romantic love are reciprocal liking, propinquity, social influence, and the filling of needs (e.g., Aron et al., 1989 ; Pines, 2001 ; Riela et al., 2010 ). Reciprocal liking (mutual attraction) is “being liked by the other, both in general, as well as when it is expressed through self-disclosure” ( Aron et al., 1989 , p. 245). It has been frequently identified as preceding romantic love among participants from the United States and is cross-culturally identified as the strongest preference in mates among both sexes ( Buss et al., 1990 ). “Whether expressed in a warm smile or a prolonged gaze, the message is unmistakable: ‘It’s safe to approach, I like you too. I’ll be nice. You’re not in danger of being rejected”’ ( Hazan and Diamond, 2000 , p. 197). Reciprocal liking may encourage the social approach and courtship activities characteristic and causative of romantic love.

Propinquity is “familiarity, in terms of having spent time together, living near the other, mere exposure to the other, thinking about the other, or anticipating interaction with the other” ( Aron et al., 1989 , p. 245). It has more recently been named “familiarity” (see Riela et al., 2010 ). The extended exposure of an individual to another helps to cause romantic love and specifically facilities the development of romantic love over extended periods of time. Propinquity, in our evolutionary history, served to ensure that “potential mates who are encountered daily at the river’s edge have an advantage over those residing on the other side” ( Hazan and Diamond, 2000 , p. 201). Given that the pool of potential mates in our evolutionary history would have been limited by the size of the groups in which we lived and the fact that most individuals of reproductive age would already have been involved in long-term mating relationships, propinquity is likely to have played a particularly important role in the generation of romantic love. Until recently (to a somewhat lesser extent, today), with the wide-scale take-up of online dating, propinquity played a role in the formation of many long-term pair-bonds, and presumably, romantic love, as is evidenced by a relatively high proportion of people having met their romantic partners in the places where exposure was facilitated, such as school, college, or work ( Rosenfeld et al., 2019 ). Changes in the importance of certain precursors in causing romantic love may be the result of a mismatch between the modern environment and our genotypes that evolved in a very different environment (discussed in detail below; see Li et al., 2018 ).

Social influences are “both general social norms and approval of others in the social network” ( Aron et al., 1989 , p. 245). This may cause people to fall in love with others who are of a similar attractiveness, cultural group, ethnic group, profession, economic class, or who are members of the same social group. Social influences may, directly, impact who we fall in love with by providing approval to a romantic union or, indirectly, by facilitating propinquity. The effect of social influences is demonstrated in the relatively large number of people who met their romantic partner through friends ( Rosenfeld et al., 2019 ). The filling of needs is “having the self’s needs met or meeting the needs of the other (e.g., he makes me happy, she buys me little presents that show she cares), and typically implies characteristics that are highly valued and beneficial in relationship maintenance (e.g., compassion, respect)” ( Riela et al., 2010 , pp. 474–475). The filling of needs may cause romantic love when social interaction facilitates a union where both partners complement each other.

Psychological Mate Choice Mechanisms

Mate choice, in the fields of evolutionary theory, can be defined as “the process that occurs whenever the effects of traits expressed in one sex lead to non-random allocation of reproductive investment with members of the opposite sex” ( Edward, 2015 , p. 301). It is essentially the process of intersexual selection proposed by Darwin (2013) more than 150 years ago ( Darwin, 1859 ) whereby someone has a preference for mating with a particular individual because of that individual’s characteristics. Mate choice, to that extent, involves the identification of a desirable conspecific ( Fisher et al., 2005 ) and sometimes, the focusing of mating energies on that individual. Mate preferences, sexual desire, and attraction all contribute to romantic love. The concepts of “extended phenotypes” and “overall attractiveness” help to explain how these features operate. Romantic love, as discussed below, serves a mate choice function ( Fisher et al., 2005 ) and these mechanisms and constructs contribute to when, and with whom, an individual falls in love.

A large body of research has developed around universal mate preferences (e.g., Buss and Barnes, 1986 ; Buss, 1989 ; Buss et al., 1990 ; Buss and Schmitt, 2019 ; Walter et al., 2020 ). Women, more than men, show a strong preference for resource potential, social status, a slightly older age, ambition and industriousness, dependability and stability, intelligence, compatibility, certain physical indicators, signs of good health, symmetry, masculinity, love, kindness, and commitment ( Buss, 1989 , 2016 ; Walter et al., 2020 ). Men, more than women, have preferences for youth, physical beauty, certain body shapes, chastity, and fidelity ( Buss, 1989 , 2016 ). Both sexes have particularly strong preferences for kindness and intelligence ( Buss et al., 1990 ). A male-taller-than-female norm exists in mate preferences and there is some evidence that women have a preference for taller-than-average height (e.g., Salska et al., 2008 ; Yancey and Emerson, 2014 ). Mutual attraction and reciprocated love are the most important characteristics that both women and men look for in a potential partner ( Buss et al., 1990 ).

Mate choice and attraction may be based on assessments of “extended phenotypes” ( Dawkins, 1982 ; Luoto, 2019a ), which include biotic and abiotic features of the environment that are influenced by an individual’s genes. For example, an extended phenotype would include an individual’s dwelling, car, pets, and social media presence. These can convey information relevant to fitness. Overall mate attractiveness, which is constituted by signs of health and fertility, neurophysiological efficiency, provisioning ability and resources, and capacity for cooperative relationships ( Miller and Todd, 1998 ) may be another heuristic through which attraction and mate choice operate.

Many mate preferences are relatively universal and therefore are likely to have at least some genetic basis (as suggested by, Sugiyama, 2015 ). While mate preferences are linked to actual mate selection ( Li et al., 2013 ; Li and Meltzer, 2015 ; Conroy-Beam and Buss, 2016 ; Buss and Schmitt, 2019 ), strong mate preferences do not always translate into real-world mate choice ( Todd et al., 2007 ; Stulp et al., 2013 ). This is in part because mate preferences function in a tradeoff manner whereby some preferences are given priority over others (see Li et al., 2002 ; Thomas et al., 2020 ). That is, mate choice is a multivariate process that includes the integration and tradeoff of several preferences ( Conroy-Beam et al., 2016 ). Mate preferences are important because they may serve as a means of screening potential mates, while sexual desire and attraction operationalize these preferences, and romantic love crystalizes them.

Sexual desire and attraction may be antecedents to falling in love and there is evidence that physiologically, sexual desire progresses into romantic love within shared neural structures ( Cacioppo et al., 2012a ). However, although both sexual desire and attraction operationalize mate choice, only attraction, and not sexual desire, may be necessary for romantic love to occur (see Leckman and Mayes, 1999 ; Diamond, 2004 ). Intense attraction is characterized by increased energy, focused attention, feelings of exhilaration, intrusive thinking, and a craving for emotional union ( Fisher, 1998 ) although it exists on a spectrum of intensity.

Changes in the expression of at least 61 genes are associated with falling in love in women ( Murray et al., 2019 ) suggesting that these genes may regulate features of romantic love. The DRD2 Taq I A polymorphism, which regulates Dopamine 2 receptor density ( Jonsson et al., 1999 ), is associated with eros ( Emanuele et al., 2007 ). Polymorphisms of genes that regulate vasopressin receptors (AVPR1a rs3), oxytocin receptors (OXTR rs53576), dopamine 4 receptors (DRD4-7R), and dopamine transmission (COMT rs4680) are associated with activity in the ventral tegmental area which, in turn, is associated with eros in newlyweds ( Acevedo et al., 2020 ).

Neurobiology

Neuroimaging studies (see Supplementary Table 2 ) implicate dozens of brain regions in romantic love. We focus, here, on only some of the most frequently replicated findings in an attempt to simplify a description of the neural activity associated with romantic love and explain its psychological characteristics. Romantic love, at least in people who are in a relationship with their loved one, appears to be associated with activity (activation or deactivation compared with a control condition) in four main overlapping systems: reward and motivation, emotions, sexual desire and arousal, and social cognition.

Reward and motivation structures associated with romantic love include those found in the mesolimbic pathway: the ventral tegmental area, nucleus accumbens, amygdala, and medial prefrontal cortex ( Xu et al., 2015 ). Activity in the mesolimbic pathway substantiates the claim that romantic love is a motivational state ( Fisher et al., 2005 ) and helps to explain why romantic love is characterized by psychological features such as longing for reciprocity, desire for complete union, service to the other, maintaining physical closeness, and physiological arousal ( Hatfield and Sprecher, 1986 ).

Emotional centers of the brain associated with romantic love include the amygdala, the anterior cingulate cortex ( Bartels and Zeki, 2000 ; Aron et al., 2005 ; Fisher et al., 2010 ; Younger et al., 2010 ; Zeki and Romaya, 2010 ; Stoessel et al., 2011 ; Acevedo et al., 2012 ; Scheele et al., 2013 ; Song et al., 2015 ), and the insula ( Bartels and Zeki, 2000 ; Aron et al., 2005 ; Ortigue et al., 2007 ; Fisher et al., 2010 ; Younger et al., 2010 ; Zeki and Romaya, 2010 ; Stoessel et al., 2011 ; Acevedo et al., 2012 ; Xu et al., 2012b ; Song et al., 2015 ). Activity in these structures helps to explain romantic love’s emotional features such as negative feelings when things go awry, longing for reciprocity, desire for complete union, and physiological arousal ( Hatfield and Sprecher, 1986 ).

The primary areas associated with both romantic love and sexual desire and arousal include the caudate, insula, putamen, and anterior cingulate cortex ( Diamond and Dickenson, 2012 ). The involvement of these regions helps to explain why people experiencing romantic love feel extremely sexually attracted to their loved one ( Hatfield and Sprecher, 1986 ). The neural similarities and overlapping psychological characteristics of romantic love and sexual desire are well documented (see Hatfield and Rapson, 2009 ; Cacioppo et al., 2012a ; Diamond and Dickenson, 2012 ).

Social cognition centers in the brain repeatedly associated with romantic love include the amygdala, the insula ( Adolphs, 2001 ), and the medial prefrontal cortex ( Van Overwalle, 2009 ). Social cognition plays a role in the social appraisals and cooperation characteristics of romantic love. Activity in these regions helps to explain psychological characteristics such as actions toward determining the other’s feelings, studying the other person, and service to the other ( Hatfield and Sprecher, 1986 ).

In addition to activity in these four systems, romantic love is associated with activity in higher-order cortical brain areas that are involved in attention, memory, mental associations, and self-representation ( Cacioppo et al., 2012b ). Mate choice (a function of romantic love detailed below) has been specifically associated with the mesolimbic pathway and hypothalamus ( Calabrò et al., 2019 ). The mesolimbic pathway, thalamus, hypothalamus, amygdala, septal region, prefrontal cortex, cingulate cortex, and insula have been specifically associated with human sexual behavior ( Calabrò et al., 2019 ), which has implications for the sex function of romantic love (detailed below).

Isolated studies have identified sex differences in the neurobiological activity associated with romantic love. One study ( Bartels and Zeki, 2004 ) found activity in the region ventral to the genu in only women experiencing romantic love. One preliminary study of romantic love (see Fisher et al., 2006 ) found that “[m]en tended to show more activity than women in a region of the right posterior dorsal insula that has been correlated with penile turgidity and male viewing of beautiful faces. Men also showed more activity in regions associated with the integration of visual stimuli. Women tended to show more activity than men in regions associated with attention, memory and emotion” (p. 2181).

Endocrinology

Romantic love is associated with changes in circulating sex hormones, serotonin, dopamine, oxytocin, cortisol, and nerve growth factor systems. Table 2 presents the endocrine factors which are found to be different, compared to controls, in people experiencing romantic love. More information about the controlled studies discussed in this subsection is presented in Supplementary Table 3 . Endocrine factors associated with romantic love have most of their psychological and other effects because of their role as a hormone (e.g., sex hormones, cortisol) or neurotransmitter (e.g., serotonin, dopamine), although many factors operate as both (see Calisi and Saldanha, 2015 ) or as neurohormones.

Significant results of controlled endocrine studies investigating romantic love.

Romantic love is associated with changes in the sex hormones testosterone, follicle-stimulating hormone, and luteinizing hormone ( Marazziti and Canale, 2004 ; Durdiakova et al., 2017 ; Sorokowski et al., 2019 ), although the findings have been inconsistent. Testosterone appears to be lower in men experiencing romantic love than controls ( Marazziti and Canale, 2004 ) and higher eros scores are associated with lower levels of testosterone in men ( Durdiakova et al., 2017 ). Lower levels of testosterone in fathers are associated with greater involvement in parenting (see Storey et al., 2020 , for review). The direction of testosterone change in women is unclear (see Marazziti and Canale, 2004 ; Sorokowski et al., 2019 ). Sex hormones are involved in the establishment and maintenance of sexual characteristics, sexual behavior, and reproductive function ( Mooradian et al., 1987 ; Chappel and Howles, 1991 ; Holloway and Wylie, 2015 ). Some sex hormones can influence behavior through their organizing effects resulting from prenatal and postnatal exposure. In the case of romantic love, however, the effects of sex hormones on the features of romantic love are the result of activating effects associated with behaviorally contemporaneous activity. It is possible that sex hormones influence individual differences in the presentation of romantic love through their organizing effect (see Motta-Mena and Puts, 2017 ; Luoto et al., 2019 ; Arnold, 2020 ; McCarthy, 2020 , for descriptions of organizing and activating effects of testosterone, estradiol, and progesterone). Changes in sex hormones could help to explain the increase in sexual desire and arousal associated with romantic love ( Hatfield and Sprecher, 1986 ; Hatfield and Rapson, 2009 ; Diamond and Dickenson, 2012 ).

Romantic love is associated with decreased serotonin transporter density ( Marazziti et al., 1999 ) and changes in plasma serotonin ( Langeslag et al., 2012 ), although inconsistencies have been found in the direction of change according to sex. In one study, men experiencing romantic love displayed lower serotonin levels than controls and women displayed higher serotonin levels than controls ( Langeslag et al., 2012 ). Decreased serotonin transporter density is indicative of elevated extracellular serotonin levels ( Mercado and Kilic, 2010 ; Jørgensen et al., 2014 ). However, decreased levels of serotonin are thought to play a role in depression, mania, and anxiety disorders ( Mohammad-Zadeh et al., 2008 ), including obsessive-compulsive disorder (for a discussion of the relationship between serotonin and OCD, see Baumgarten and Grozdanovic, 1998 ; Rantala et al., 2019 ). One study showed that a sample of mainly women (85% women) experiencing romantic love have similar levels of serotonin transporter density to a sample of both women and men (50% women) with obsessive-compulsive disorder ( Marazziti et al., 1999 ), which could account for the intrusive thinking or preoccupation with the loved one associated with romantic love ( Hatfield and Sprecher, 1986 ).

Lower dopamine transporter density and lower dopamine transporter maximal velocity in lymphocytes have been found in people experiencing romantic love ( Marazziti et al., 2017 ). This is indicative of increased dopamine levels ( Marazziti et al., 2017 ) and is consistent with neuroimaging studies (e.g., Takahashi et al., 2015 ; Acevedo et al., 2020 ) showing activation of dopamine-rich regions of the mesolimbic pathway. One study ( Dundon and Rellini, 2012 ) found no difference in dopamine levels in urine in women experiencing romantic love compared with a control group. Dopamine is involved in reward behavior, sleep, mood, attention, learning, pain processing, movement, emotion, and cognition ( Ayano, 2016 ). Up-regulation of the dopamine system could help to explain the motivational characteristics of romantic love such as longing for reciprocity, desire for complete union, service to the other, and maintaining physical closeness ( Hatfield and Sprecher, 1986 ).

There are no studies that have specifically investigated oxytocin levels in romantic love (at least none that measure romantic love with a validated scale). However, studies ( Schneiderman et al., 2012 , Schneiderman et al., 2014 ; Ulmer-Yaniv et al., 2016 ) have demonstrated that people in the early stages of their romantic relationship have higher levels of plasma oxytocin than controls (singles and new parents). We infer this to mean that reciprocated romantic love is associated with elevated oxytocin levels. Oxytocin plays a role in social affiliation ( IsHak et al., 2011 ) and pair-bonding ( Young et al., 2011 ; Acevedo et al., 2020 ). Oxytocin receptors are prevalent throughout the brain including in the mesolimbic pathway (e.g., Bartels and Zeki, 2000 ). Elevated oxytocin could account for many of the behavioral features of romantic love such as actions toward determining the other’s feelings, studying the other person, service to the other, and maintaining physical closeness ( Hatfield and Sprecher, 1986 ).

Romantic love has been associated with elevated cortisol levels ( Marazziti and Canale, 2004 ), although this has not been replicated ( Sorokowski et al., 2019 ), and one study measuring cortisol in saliva found the opposite ( Weisman et al., 2015 ). Different results could be attributed to different length of time in a relationship between the samples (see Garcia, 1997 ; de Boer et al., 2012 ). Cortisol plays a role in the human stress response by directing glucose and other resources to various areas of the body involved in responding to environmental stressors while simultaneously deactivating other processes (such as digestion and immune regulation, Mercado and Hibel, 2017 ). Elevated cortisol levels may play a role in pair-bond initiation ( Mercado and Hibel, 2017 ) and are indicative of a stressful environment.

Romantic love is associated with higher levels of nerve growth factor, and the intensity of romantic love correlates with levels of nerve growth factor ( Emanuele et al., 2006 ). Nerve growth factor is a neurotrophic implicated in psycho-neuroendocrine plasticity and neurogenesis ( Berry et al., 2012 ; Aloe et al., 2015 ; Shohayeb et al., 2018 ) and could contribute to some of the neural and endocrine changes associated with romantic love.

Insights From the Mechanisms of Psychopathology

Despite “madness” being mentioned in one review of the neurobiology of love ( Zeki, 2007 ) and psychopathology being discussed in studies investigating the endocrinology of romantic love (e.g., Marazziti et al., 1999 , 2017 ), the similarities between romantic love and psychopathology are under-investigated. An understanding of the mechanisms that regulate addiction, mood disorders, and anxiety disorders may help to shed light on the psychological characteristics and mechanisms underlying romantic love and identify areas for future research.

Conceptualizing romantic love as a “natural addiction” (e.g., Fisher et al., 2016 ) not only helps to explain romantic love’s psychological characteristics but provides insight into the mechanisms underlying it (e.g., Zou et al., 2016 ). For example, a neurocircuitry analysis of addiction, drawing on human and animal studies, reveals mechanisms of different “stages” of addiction that have implications for romantic love: binge/intoxication (encompassing drug reward and incentive salience), withdrawal/negative affect, and preoccupation/anticipation ( Koob and Volkow, 2016 ). Each of these stages is associated with particular neurobiological activity and each stage could be represented in romantic love. This may mean that the findings of studies investigating the neurobiology of romantic love (which rely primarily on studies where visual stimuli of a loved one are presented) equates to the binge/intoxication stage of addiction. Findings from studies investigating romantic rejection ( Fisher et al., 2010 ; Stoessel et al., 2011 ; Song et al., 2015 ) may equate to the withdrawal/negative affect stage of addiction. Findings from resting-state fMRI studies ( Song et al., 2015 ; Wang et al., 2020 ) may equate to the preoccupation/anticipation stage of addiction. The result is that current neuroimaging studies may paint a more detailed picture of the neurobiology of romantic love than might initially be assumed.

Mood is an emotional predictor of the short-term prospects of pleasure and pain ( Morris, 2003 ). The adaptive function of mood is, essentially, to integrate information about the environment and state of the individual to fine-tune decisions about behavioral effort ( Nettle and Bateson, 2012 ). Elevated mood can serve to promote goal-oriented behavior and depressed mood can serve to extinguish such behavior ( Wrosch and Miller, 2009 ; Bindl et al., 2012 ; Nesse, 2019 ). Anxious mood is a response to repeated threats ( Nettle and Bateson, 2012 ). Because romantic love can be a tumultuous time characterized by emotional highs, lows, fear, and trepidation, and can involve sustained and repetitive efforts to pursue and retain a mate, it follows that mood circuitry would be closely intertwined with romantic love. Additionally, because romantic love concerns itself with reproduction, which is the highest goal in the realm of evolutionary fitness, it makes sense that mood may impact upon the way romantic love manifests. Understanding the mechanisms that regulate mood can provide insights into psychological characteristics of romantic love and the mechanisms that regulate it. No studies have directly investigated the mechanisms that contribute to changes in mood in people experiencing romantic love. However, insights can be taken from research into the mechanisms of mood and anxiety disorders.

While addiction, hypomania, depression, and anxiety symptoms in people experiencing romantic love may be the normal manifestation of particular mechanisms, symptoms associated with psychopathology may be the manifestations of malfunctioning mechanisms as a result of evolutionary mismatch (see Durisko et al., 2016 ; Li et al., 2018 ). As a result, the mechanisms that cause romantic love and those that cause psychopathology may not be precise models with which to investigate the other. Nonetheless, the mechanisms that cause psychopathology may provide a useful framework with which to base future research into romantic love. Conversely, it may also be that our understanding of the mechanisms that cause romantic love could be a useful framework with which to further investigate psychopathology.

The drug reward and incentive salience features of the binge/intoxication stage of addiction involve changes in dopamine and opioid peptides in the basal ganglia (i.e., striatum, globus pallidus, subthalamic nucleus, and substantia nigra pars reticulata, Koob and Volkow, 2016 ). No research has investigated opioids in romantic love, despite them being involved in monogamy in primates (see French et al., 2018 ) and pair-bonding in rodents ( Loth and Donaldson, 2021 ). The negative emotional states and dysphoric and stress-like responses in the withdrawal/negative affect stage are caused by decreases in the function of dopamine in the mesolimbic pathway and recruitment of brain stress neurotransmitters (i.e., corticotropin-releasing factor, dynorphin), in the extended amygdala ( Koob and Volkow, 2016 ). No studies have investigated corticotropin-releasing factor in romantic love. The craving and deficits in executive function in the preoccupation/anticipation stage of addiction involve the dysregulation of projections from the prefrontal cortex and insula (e.g., glutamate), to the basal ganglia and extended amygdala ( Koob and Volkow, 2016 ). No studies have investigated glutamate in romantic love. There are at least 18 neurochemically defined mini circuits associated with addiction ( Koob and Volkow, 2016 ) that could be the target of research into romantic love. It is likely that romantic love has similar, although not identical, mechanisms to addiction (see Zou et al., 2016 ; Wang et al., 2020 ).

Mania/hypomania (bipolar disorder)

Similar to the brain regions implicated in romantic love, the ventral tegmental area has been associated with mania ( Abler et al., 2008 ), the ventral striatum has been associated with bipolar disorder ( Dutra et al., 2015 ), and the amygdala has been associated with the development of bipolar disorder ( Garrett and Chang, 2008 ). These findings should be interpreted with caution, however, as replicating neuroimaging findings in bipolar disorder has proven difficult (see Maletic and Raison, 2014 ). Research implicates two interrelated prefrontal–limbic networks in elevated mood, which overlap with activity found in romantic love: the automatic/internal emotional regulatory network which includes the ventromedial prefrontal cortex, subgenual anterior cingulate cortex, nucleus accumbens, globus pallidus, and the thalamus, and the volitional/external regulatory network which includes the ventrolateral prefrontal cortex, mid- and dorsal-cingulate cortex, ventromedial striatum, globus pallidus, and thalamus ( Maletic and Raison, 2014 ).

Norepinephrine (theorized to be involved in romantic love, e.g., Fisher, 1998 , 2000 ), serotonin, dopamine, and acetylcholine play a role in bipolar disorder ( Manji et al., 2003 ). One study ( Dundon and Rellini, 2012 ) found no difference in norepinephrine levels in urine in women experiencing romantic love compared with a control group. No studies have investigated acetylcholine in romantic love but romantic love is associated with serotonin ( Marazziti et al., 1999 ; Langeslag et al., 2012 ) and dopamine activity ( Marazziti et al., 2017 ). Similar to the endocrine factors implicated in romantic love ( Emanuele et al., 2006 ; Schneiderman et al., 2012 , 2014 ; Ulmer-Yaniv et al., 2016 ), bipolar patients in a period of mania have also demonstrated higher oxytocin ( Turan et al., 2013 ) and nerve growth factor ( Liu et al., 2014 ) levels and lower levels of serotonin ( Shiah and Yatham, 2000 ). Additionally, there is some evidence that women diagnosed with bipolar disorder present with higher levels of testosterone whereas men present with lower levels of testosterone compared with sex-matched controls ( Wooderson et al., 2015 ). Similar findings have been found in romantic love ( Marazziti and Canale, 2004 ). Dysfunction in the hypothalamic–pituitary–adrenal axis, where cortisol plays a major role, has also been implicated in bipolar disorder ( Maletic and Raison, 2014 ). Cortisol probably plays a role in romantic love ( Marazziti and Canale, 2004 ; Weisman et al., 2015 ).

Neuroimaging studies have implicated changes in functional connectivity in the neural circuits involved in affect regulation in people experiencing depression ( Dean and Keshavan, 2017 ). Increased functional connectivity has been found in networks involving some of the same regions, such as the amygdala, the medial prefrontal cortex, and nucleus accumbens in both people experiencing romantic love and people who recently ended their relationship while in love ( Song et al., 2015 ).

There are a number of endocrine similarities between romantic love and depression. One major pathophysiological theory of depression is that it is caused by an alteration in levels of one or more monoamines, including serotonin, norepinephrine, and dopamine ( Dean and Keshavan, 2017 ). Altered dopamine transmission in depression may be characterized by a down-regulated dopamine system (see Belujon and Grace, 2017 ), which is inferred from numerous human and animal studies, including successful treatment in humans with a dopamine agonist. In romantic love, however, dopamine appears to be up-regulated, especially in areas of the mesolimbic pathway (e.g., Marazziti et al., 2017 ; Bartels and Zeki, 2000 ; Acevedo et al., 2020 ). This could account for some findings that romantic love is associated with a reduction in depression symptoms ( Bajoghli et al., 2013 , 2017 ). However, these need to be reconciled with contrasting findings that romantic love is associated with increased depression symptoms ( Bajoghli et al., 2014 ; Kuula et al., 2020 ) and evidence suggesting that a relationship breakup in people experiencing romantic love is associated with depression symptoms ( Stoessel et al., 2011 ; Price et al., 2016 ; Verhallen et al., 2019 ). The mechanisms that underlie depression might provide a framework for such efforts.

Dysregulation of the HPA axis and associated elevated levels of cortisol is theorized to be one contributor to depression ( Dean and Keshavan, 2017 ). Changes in oxytocin and vasopressin systems (theorized to be involved in romantic love, e.g., Fisher, 1998 , 2000 ; Carter, 2017 ; Walum and Young, 2018 ) are associated with depression (see Purba et al., 1996 ; Van Londen et al., 1998 ; Neumann and Landgraf, 2012 ; McQuaid et al., 2014 ). No studies have investigated vasopressin in people experiencing romantic love. There is also decreased neurogenesis and neuroplasticity in people experiencing depression ( Dean and Keshavan, 2017 ), the opposite of which can be inferred to occur in romantic love because of its substantial neurobiological activity and elevated nerve growth factor (see Berry et al., 2012 ; Aloe et al., 2015 ; Shohayeb et al., 2018 ).

The insular cortex, cingulate cortex, and amygdala are implicated in anxiety and anxiety disorders ( Martin et al., 2009 ). There is also evidence that cortisol, serotonin and norepinephrine are involved ( Martin et al., 2009 ). The substantial overlap between the mechanisms regulating romantic love and those causing anxiety and anxiety disorders provides an opportunity to investigate specific mechanistic effects on the psychological characteristics of romantic love. Assessing state anxiety and these mechanisms concurrently in people experiencing romantic love may be a fruitful area of research.

There is also a need to clarify the role of the serotonin system in romantic love. Similar serotonin transporter density in platelets in people experiencing romantic love and OCD suggests a similar serotonin-related mechanism in both ( Marazziti et al., 1999 ). However, lower serotonin transporter density in platelets is indicative of higher extracellular serotonin levels ( Mercado and Kilic, 2010 ; Jørgensen et al., 2014 ). This is despite lower levels of serotonin being theorized to contribute to anxiety ( Mohammad-Zadeh et al., 2008 ). One study found lower circulating serotonin levels in men experiencing romantic love than controls and higher levels of circulating levels of serotonin in women experiencing romantic love than controls ( Langeslag et al., 2012 ). Insights from the mechanisms regulating anxiety disorders may help to provide a framework with which to further investigate the role of the serotonin system in romantic love and reconcile these findings.

Insights From Cognitive Biases

Positive illusions are cognitive biases about a relationship and loved one that are thought to have positive relationship effects ( Song et al., 2019 ). The research into positive illusions does not use samples of people explicitly experiencing romantic love, and instead uses people in varied stages of a romantic relationship, including those in longer-term pair-bonds. One study ( Swami et al., 2009 ), however, did find a correlation between the “love-is-blind bias” (one type of positive illusion) and eros scores. We also know that cognitive biases resembling positive illusions do exist in romantic love. Both the Passionate Love Scale (e.g., “For me, ____ is the perfect romantic partner,” Hatfield and Sprecher, 1986 , p. 391) and the eros subscale of the Love Attitudes Scale (e.g., “My lover fits my ideal standards of physical beauty/handsomeness,” Hendrick and Hendrick, 1986 , p. 395) include questions about a respondent’s loved one that resemble measures of positive illusions. Understanding the mechanism that regulates positive illusions will provide a model against which the mechanisms regulating the cognitive features of romantic love can be assessed.

A proposed mechanism of positive illusions includes the caudate nucleus, dorsal anterior cingulate cortex, ventral anterior cingulate cortex, orbitofrontal cortex, ventrolateral prefrontal cortical regions, and dorsal medial prefrontal cortex ( Song et al., 2019 ). These regions overlap with the brain regions associated with romantic love. This suggests that the cognitive biases associated with romantic love may be related to, but are distinct from, positive illusions. Targeted neuroimaging studies could ascertain any involvement of the ventrolateral prefrontal cortex and the dorsal medial prefrontal cortex in romantic love. Such research could help to delineate a mechanism that specifically regulates one cognitive aspect of romantic love from those that regulate other psychological aspects of romantic love.

Insights From Mammalian Pair-Bonding Mechanisms

It is not possible to say with any certainty if other animals experience romantic love. Some certainly engage in pair-bonding and exhibit behaviors that are characteristic of romantic love such as obsessive following, affiliative gestures, and mate guarding (see Fisher et al., 2006 ). While some similarities between humans and other animals may be the result of parallel evolution, an understanding of the mechanisms involved in pair-bond formation in other animals can raise questions and guide research into romantic love in humans. Research into monogamous prairie voles, in particular, has identified neurobiological and endocrinological mechanisms that regulate pair-bonding processes. Drawing on this research, a hypothetical neural circuit model of pair-bond formation (pair-bonding) that includes the ventral tegmental area, nucleus accumbens, paraventricular nucleus, amygdala, hippocampus, anterior olfactory nucleus, and medial prefrontal cortex has been proposed ( Walum and Young, 2018 ). Research implicates oxytocin, vasopressin, dopamine, and, potentially, serotonin and cortisol in pair-bonding ( Walum and Young, 2018 ). Most of these neural regions and endocrine factors have been implicated in romantic love in humans. The implications of this research become apparent when the phylogeny of romantic love is presented.

When applied to romantic love, the second of Tinbergen’s (1963) four questions asks: “How does romantic love develop over the lifetime of an individual?” This can be answered with reference to the age of onset of romantic love, its presence throughout the lifespan, and its duration. Questions of ontogeny also encompass issues around the internal and external influences on romantic love ( Tinbergen, 1963 ; Zeifman, 2001 ). We have also chosen to include some consideration of culture in this section because it influences the causes of romantic love. We find that romantic love first develops in childhood, is experienced at all ages in both sexes, usually lasts months or years, but can exist for many years or decades. It is influenced by a range of internal and external factors and is similar across cultures. The modern environment may influence romantic love in ways not present in our evolutionary history.

Romantic Love Over the Lifetime

Romantic love occurs from childhood through adulthood. It first manifests before puberty ( Hatfield et al., 1988 ), with boys and girls as young as four reporting experiences that equate to romantic love. Adolescence is the time in which romantic love first manifests with all of its characteristic features ( Hatfield and Sprecher, 1986 ), including the onset of sexual desire and activity and, potentially, pair-bonding. Romantic love may be more common among adolescents than young adults. In one study ( Hill et al., 1997 ), American university psychology students reported a greater occurrence of mutual and unrequited love experiences when they were 16–20 years old compared to when they were 21–25 years old. However, romantic love exists at all ages of adulthood in both sexes ( Wang and Nguyen, 1995 ).

There are few studies of psychological sex differences in romantic love. Those that exist (e.g., Hatfield and Sprecher, 1986 ; Hendrick and Hendrick, 1995 ; Cannas Aghedu et al., 2018 ) compare the overall intensity of romantic love and find no difference or slightly more intense romantic love in women than men. To our knowledge, no research has specifically investigated sex differences in duration or form of romantic love although it has been shown that some precursors to romantic love may play a greater role in one sex than the other (see Pines, 2001 ; Sprecher et al., 1994 ; Riela et al., 2010 ). As highlighted above, there are small sex differences in the neurobiology of romantic love ( Bartels and Zeki, 2004 ; Fisher et al., 2006 ) and sex differences may exist in the activity of testosterone ( Marazziti and Canale, 2004 ) and serotonin ( Langeslag et al., 2012 ) in people experiencing romantic love, although findings have been inconsistent. These neurobiological and endocrinological differences may, presumably, have differential effects on the presentation of romantic love which have not yet been identified by research.

The psychological features of romantic love are said to normally last between 18 months to 3 years ( Tennov, 1979 ), although studies have found that serotonin transporter density, cortisol levels, testosterone levels, follicle-stimulating hormone levels, and nerve growth factor levels do not differ from controls 12–24 months after initial measurement ( Marazziti et al., 1999 ; Marazziti and Canale, 2004 ; Emanuele et al., 2006 ). Unrequited love has been shown to last an average duration of between 10 and 17 months, depending on the type of unrequited love ( Bringle et al., 2013 ). In that study, unrequited love for someone that an individual pursued lasted the shortest period of time (10.12 months) and romantic love for someone who an individual knows but has not revealed their love to lasted the longest (18.44 months) in a sample of high school and university students from the United States. This contrasts with reciprocated romantic love that lasted even longer (an average of 21.33 months).

The early stages of romantic love characterized by stress may be distinct from a later period characterized by feelings of safety and calm ( Garcia, 1997 ; de Boer et al., 2012 ). The first stage, which is characterized by approximately the first 6 months of a relationship, has been described as “being in love.” It is marked by all the characteristics of romantic love, including, especially, romantic passion and intimacy. The second phase, which has been said to last from approximately 6 months to 4 years, has been referred to as “passional love.” During this time passion is maintained but commitment and intimacy increase. Passional love gives way to companionate love, passion subsides, and commitment and intimacy reach their peaks. While a description of these phases is informative, it is important to recognize that only one study has investigated these phases and they used a sample of predominately university students ( Garcia, 1997 ). Mechanisms research has not adopted these stages and “early stage” romantic love does not specifically refer to the first 6 months of a romantic relationship.

Romantic love exists on a continuum of intensity but can be classified categorically ( Hatfield and Sprecher, 1986 ). The authors of the Passionate Love Scale ( Hatfield and Sprecher, 2011 ) have developed arbitrary cutoffs for differing intensities of romantic love. However the thresholds that define them are not theoretically or empirically derived and are yet to be widely accepted in the literature.

Romantic love can commence abruptly or build up slowly, although the phenomenon of “love at first sight” may actually be strong attraction rather than romantic love, per se ( Sternberg, 1986 ; Zsok et al., 2017 ). In one study of Chinese and American participants, 38% of participants fell in love fast and 35% fell in love slow, with the remaining unknown ( Riela et al., 2010 ). Another study, of Iranians, found that 70% of participants fell in love slowly or very slowly ( Riela et al., 2017 ). Romantic love can end abruptly but often wanes slowly.

Regardless of the normal duration of romantic love, there is a general inverse relationship between the length of time in a relationship and romantic love ( Hatfield et al., 2008 ; Acevedo and Aron, 2009 ). Romantic love normally gives way to failure of a relationship to form, a relationship breakup, or transition to companionate love. However, in some individuals, romantic love can last many years, or even, decades ( O’Leary et al., 2011 ; Acevedo et al., 2012 ; Sheets, 2013 ). In romantic relationships that last, romantic love serves to bond partners together by creating shared understandings, emotions, and habits ( Hatfield and Walster, 1985 ) characteristic of companionate love and long-term pair-bonds. The transition from romantic love to companionate love is gradual and both types of love share many characteristics. In circumstances where romantic love is maintained beyond the initial few years, obsessive thinking about a partner is no longer a feature (e.g., Acevedo and Aron, 2009 ; O’Leary et al., 2011 ).

Internal and External Influences

A number of internal and external influences affect when, with whom, and how we fall in love. The scenario of attachment, separation, and loss in young children ( Bowlby, 1969 , 1973 , 1980 ) is similar to a “desire for union” and may be the groundwork for romantic attachments in later life ( Hatfield et al., 1988 ). To this extent, romantic love, like newborn/infant attachment, is “prewired” into humans as part of their evolutionary heritage ( Hatfield et al., 1989 ). Researchers “focus their investigations on the effects of mother-infant bonding in order to explain variations in the form, duration, and/or frequency of adult passionate relationships” ( Fisher, 1998 , p. 31). For example, a person’s adult attachment style is determined in part by childhood relationships with parents ( Hazan and Shaver, 1987 ) and this may have implications for the experience of romantic love (e.g., Hendrick and Hendrick, 1989 ; Aron et al., 1998 ). Romantic love is positively associated with a secure attachment style and negatively associated with an avoidant attachment style.

Precursors to romantic love include reciprocal liking, appearance, personality, similarity, social influence, filling needs, arousal, readiness, specific cues, isolation, mysteriousness, and propinquity (see Aron et al., 1989 ; Sprecher et al., 1994 ; Riela et al., 2010 ; Riela et al., 2017 ; see also Hazan and Diamond, 2000 ; Fisher, 2011 ). Research also suggests that conscious variables (personality and appearance), situational variables (proximity and arousal), lover variables (lover finds us attractive, lover fills important needs, similarity, and lover is best friend), and unconscious variables (similarity to relationship with parents, similarity of lover to father, similarity of lover to mother, and love at first sight) contribute to with whom we fall in love ( Pines, 2005 ). The majority of precursors are an interplay between internal and external influences.

Some of the most important precursors to romantic love include personality, reciprocal liking, physical appearance, propinquity, specific cues, readiness, and similarity ( Aron et al., 1989 ; Sprecher et al., 1994 ; Riela et al., 2010 , 2017 ). Personality is the “attractiveness of the other’s personality (e.g., intelligent, humorous)” ( Riela et al., 2010 , p. 474). This represents an interplay between internal influences (the preferences of the individual or what they find attractive) and external influences (the personality characteristics of the potential loved one). Reciprocal liking has been defined above and is a mixture of internal and external influences. Physical appearance, too, is an interplay between what an individual finds attractive, either through genetic predisposition or learned experience, and the physical attributes of the potential loved one. Propinquity has been defined and discussed above and is a combination of internal and external influences. Similarity is “having things in common, including attitudes, experiences, interests, and personal factors such as appearance, personality, and family background ( Riela et al., 2010 , p. 474). This is contingent upon both the individual’s characteristics (internal influence) and the potential loved one’s characteristics (external influence).

There are, however, some precursors that are explicitly internal or external influences. Readiness is “being emotionally or physically prepared for seeking a romantic relationship, such as having just broken up with someone and seeking comfort in a new partner” ( Riela et al., 2010 , p. 475). This can be a largely internal influence that can cause romantic love. Specific cues are “particular characteristics of the other (e.g., smile, shape of the eyes), that are relevant to the perceiver in producing strong attractions. This is not the same as attractiveness in general but refers to highly idiosyncratic features of potential love objects that are specifically important to the individual” ( Riela et al., 2010 , p. 475). These are largely external influences that cause romantic love, although they do trigger a biological or psychological response which is internally determined.

Cross-Cultural Perspectives

There have been a number of books (e.g., Jankowiak, 1995 , 2008 ) and studies that shed light on the cross-cultural nature of romantic love. The sum of research indicates that romantic love is probably universal (although the research is yet to prove this unequivocally) with relatively few psychological differences found between cultures (although cultures respond to love in different ways). An ethnographic analysis of 166 cultures from the Standard Cross-Cultural Sample ( Jankowiak and Fischer, 1992 ; Jankowiak and Paladino, 2008 ) found no evidence of romantic love in only 15 cultures, and this was largely due to lack of data. Validated measures of romantic love (i.e., Passionate Love Scale, Love Attitudes Scale, Triangular Love Scale) have been used in at least 50 countries ( Feybesse and Hatfield, 2019 ). The Triangular Theory of Love is robust cross-culturally ( Sorokowski et al., 2020 ). Cross-cultural accounts of the features and the intensity of romantic love are remarkably similar (see Feybesse and Hatfield, 2019 for a review of cross-cultural perspectives on romantic love). Multiple neuroimaging studies have ascertained that the same neural mechanisms associated with romantic love in American samples are associated with romantic love in Chinese samples ( Xu et al., 2011 , 2012b ).

Romantic love may be thought of more positively among Western countries than other countries and Westerners report falling in love more often (see Feybesse and Hatfield, 2019 ). Cultural differences have also been identified in the role of precursors in causing romantic love. A comparison between Japanese, Russian, and American populations found that culture played a role in the self-reported importance of personality, physical appearance, propinquity, similarity, readiness, isolation, mystery, and social standing ( Sprecher et al., 1994 ). Some differences have also been found between Chinese and Americans ( Riela et al., 2010 ) and between Iranians and Americans ( Riela et al., 2017 ) using similar and different methods. In some cultures, romantic love is suppressed and arranged marriages predominate (discussed below).

Evolutionary Mismatch

The evolutionary mismatch hypothesis argues that humans are now living in environments vastly different from those in which they evolved and, as a result, biological mechanisms may not interact with the environment in the manner that they originally evolved to Li et al. (2018) . Adaptations may malfunction. This has implications for the functioning of mechanisms and psychology. Evolutionary mismatch may influence the occurrence, duration, form, and experience of romantic love. As already suggested, evolutionary mismatch may influence the degree to which certain social mechanisms play a role in causing romantic love. This may have flow-on impacts on the frequency with which an individual falls in love or with whom they fall in love. The increased exposure to potential mates may also lead to greater instances of relationship dissolution and new instances of romantic love than would have been the case in our evolutionary history. Evolutionary mismatch may also influence the duration of romantic love. Under evolutionary conditions, romantic love would usually occur in the context of reproduction, pregnancy, and childbirth (see Goetz et al., 2019 ). This may mean that the duration of romantic love may have been shorter in females than is the case in modern developed societies because they are overcome by mother-infant bonding, possibly at the expense of romantic love.

The form and experience of romantic love may also be impacted by evolutionary mismatch. Technology means that lovers are able to maintain regular contact (e.g., by telephone) or be exposed to images of the loved one (e.g., by photographs) in the absence of physical contact. This consistent exposure may be associated with more frequent activation of neural structures associated with romantic love (i.e., reward and motivation structures) and change the intensity or subjective experience of romantic love compared to evolutionary ancestors who may have been completely separated for periods of time.

Ultimate Perspectives

When applied to romantic love, the third of Tinbergen’s (1963) four questions asks: “What are the fitness-relevant functions of romantic love?” Functional explanations address the fitness ramifications (survival and reproduction) of the behavior or trait of interest ( Tinbergen, 1963 ; Zeifman, 2001 ; Bateson and Laland, 2013 ). We are, thus, concerned with both the fitness-relevant benefits and costs of romantic love. We have outlined the benefits and costs of romantic love associated with five functions based on a small literature on the subject (i.e., Fletcher et al., 2015 ; Buss, 2019 ), reproduction-related literature, and our consideration of the subject. Some of the benefits we describe can be considered functions in their own right (e.g., Buss, 2019 ). Table 3 presents a summary of benefits and costs of romantic love according to five distinct yet interrelated functions: mate choice, courtship, sex, pair-bonding, and health. Our approach is to describe each function, present the benefits associated with each function, and present the costs associated with each function. Where relevant, we have included information about related concepts or theories. We contend that while there is a small amount of evidence for the health promoting benefits of romantic love, the evidence is insufficient to say with certainty that health promotion is a function of romantic love. We conclude this section by summarizing some potential selective pressures and describing romantic love as a complex suite of adaptations and by-products.

Reproduction- and survival-related benefits and costs associated with each function of romantic love.

Mate Choice

Romantic love serves a mate choice function ( Fisher et al., 2006 ). Both men and women engage in mate choice ( Stewart-Williams and Thomas, 2013 ). Assessing potential mates has important fitness consequences for individuals, as the benefits of finding a suitable mate are often higher than mating haphazardly or with a randomly selected mate ( Geary et al., 2004 ; Andersson and Simmons, 2006 ; Jones and Ratterman, 2009 ; Shizuka and Hudson, 2020 ). On the other hand, mate choice is a costly and error-prone activity and, thus, it may be adaptive to focus one’s attention on a particular mate that has been identified as a preferred partner ( Bowers et al., 2012 ). Romantic love serves this function.

Mate choice evolved in mammals to enable individuals to conserve their mating energy, choose between potential mates, and focus their attention on particular potential mating partners ( Fisher, 2000 ; Fisher et al., 2006 ). The focus of one’s attention on a single potential mate is not without costs (e.g., Klug, 2018 ; Bear and Rand, 2019 ). Imperfect mate choice (e.g., Johnstone and Earn, 1999 ) could result from imperfect information (e.g., Luttbeg, 2002 ) or acceptance or rejection errors. Imperfect information might include the concealment of information that has detrimental effects on fitness. Time to assess an individual is important in mate choice and imperfect mate choice could potentially be a greater problem in circumstances where romantic love is quick to arise. Mate choice, by definition, excludes other potential mates and romantic love, in fact, suppresses the search for other mates ( Fletcher et al., 2015 ). This cost can be exacerbated in certain environments such as those within which finding additional mates is relatively easy ( Kushnick, 2016 ). Romantic love can detract from other fitness-promoting goals such as career-advancing activities, physical health promoting activities, or forming and maintaining other social relationships.

Romantic love serves a courtship function ( Fisher et al., 2006 , 2016 ). Courtship involves a series of signals and behaviors that serve as a means of assessing potential partner quality and willingness to invest in a relationship ( Trivers, 1972 ; Wachtmeister and Enquist, 2000 ). One function of the attraction system is to pursue potential mates ( Fisher, 2000 ). People in love often engage in courtship of their loved one with the aim of persuading them that they are a good long-term mate.

The primary benefit of courtship in romantic love is that it can secure a mate that is prepared to commit to a relationship. To do this, both sexes can pursue potential mates, display commitment, and signal fidelity ( Buss, 2019 ). These acts are why love has been described as a commitment device ( Frank, 1988 ; Fletcher et al., 2015 ; Buss, 2019 ). Courtship allows individuals to learn about and assess the suitability of potential mates while displaying reproductively relevant resources ( Buss, 2019 ). Men emphasize characteristics such as resources, while women emphasize characteristics such as beauty, in an attempt to increase attractiveness ( Buss, 1988 ; Luoto, 2019a ). Men, at least historically, also provide signals of parental investment ( Buss, 2019 ). Literature on human courtship from an evolutionary perspective supports the notion of greater choosiness among females, predicted by parental investment theory ( Trivers, 1972 ), for short-term mating and less serious commitments. This effect, however, substantially diminishes for long-term mating endeavors and marriage commitment ( Kenrick et al., 1990 ). The literature also suggests that women are looking for specific cues, indicative of evolved preferences, during the courtship process ( Oesch and Miklousic, 2012 ).

There are costs associated with romantic love’s courtship function. These include the expenditure of a significant amount of time and resources and, if courtship efforts are not reciprocated, embarrassment ( Silver et al., 1987 ). Sometimes, individuals in love might engage in intrusive “obsessive pursuit” of someone who is not interested ( Spitzberg and Cupach, 2003 ). Courtship can be a particularly stressful time for an individual. There are also potential costs because individuals who are courting might find themselves in direct intrasexual competition with another individual who has an interest in their potential mate. Intrasexual competition can be costly because an individual must divert additional resources to this endeavor. An individual bears even greater costs if they lose this competition. Both sexes can be subject to costly signaling as part of courtship ( Griskevicius et al., 2007 ), although men are at risk of higher fitness costs associated with temporally extended courtships, despite this being interpreted as a sign of a good mate by women ( Seymour and Sozou, 2009 ).

Romantic love promotes sex and may increase the chances of pregnancy. Sex is an important part of romantic relationships and initiation into sex with a partner, and a greater frequency of sex, is associated with the earlier stages of a romantic relationship ( Call et al., 1995 ). Sex and pregnancy are not, however, features of romantic love in pre-pubescent children and pregnancy is not a feature of romantic love in post-menopausal women. The nature of reproduction is different in societies where contraception and family planning practices are widespread (see Goetz et al., 2019 , for review of evolutionary mismatch in human mating). In such circumstances, immediate pregnancy may not be a feature of romantic love, whereas sex often is. In such circumstances, romantic love may indirectly promote pregnancy by creating pair-bonds whose members later reproduce.

Romantic love provides sexual access ( Buss, 2019 ). Love is one of the most common reasons people give for having sex ( Ozer et al., 2003 ; Meston and Buss, 2007 ; Dawson et al., 2008 ; Meston and Buss, 2009 ). Given the relative willingness of men to engage in short-term mating compared to women, it follows that sex because of love plays a greater role in providing sexual access by women to men than the other way around ( Meston and Buss, 2007 ). Sex can facilitate a gain in reputation ( Meston and Buss, 2007 ) and both sexes increase their status by having children ( Buss et al., 2020 ). Sex is intrinsically pleasurable and reinforcing, and promotes bonding ( Meltzer et al., 2017 ). In times before the advent of contraception, repeated sex with a partner would usually result in pregnancy and childbirth ( Goetz et al., 2019 ; Kushnick, 2019 ). This is still the case in many parts of the world.

For example, there is evidence that features characteristic of romantic love may be associated with a greater number of children among the Hadza, a hunter gatherer tribe in northern Tanzania ( Sorokowski et al., 2017 ). Higher passion, which is definitive of romantic love (e.g., Sternberg, 1986 ), is associated with a greater number of children in women. The findings are important because the lifestyle of the Hadza more closely resembles the environment in which humans evolved than do industrialized or agrarian societies. As a result, inferences can be made about the adaptive function of passion in human evolutionary history. However, intimacy, another component of romantic love ( Sternberg, 1997 ), was found to be negatively correlated with number of children in women. Instead, commitment, a feature of companionate love, was associated with greater number of children in both women and men ( Sorokowski et al., 2017 ). Romantic love is normally relatively short-lived, and therefore the methods used in this study may not have been ideally suited to investigate the fitness consequences of romantic love. Nonetheless, this finding provides some support for the notion that romantic love promotes sexual access by women and facilitates reproduction.

One study ( Sorokowski et al., 2019 ) suggests that romantic love may increase the likelihood of a woman falling pregnant. Higher levels of the gonadotropins, follicle-stimulating hormone, and luteinizing hormone, and a non-significant but positive increase in estradiol to testosterone ratio in women experiencing romantic love could cause increased ovarian activity and increased estradiol synthesis, which might result in higher fecundity ( Sorokowski et al., 2019 ).

The costs associated with romantic love’s sex function are far greater for women than for men ( Trivers, 1972 ). Both sexes could be subject to unwanted pregnancy and associated parenting responsibilities (although this impacts women to a greater extent). There is also, however, a risk of damage to an individual’s reputation. Women are often subject to criticism from other women for engaging in sexual activity ( Koehn and Jonason, 2018 ), especially if a long-term relationship does not result. Men and women risk damage to their reputation for having sex with a low mate value partner, although men are generally treated far more favorably than women for engaging in sexual activity (see Zaikman and Marks, 2017 ). For women, a period of pregnancy followed by a lengthy period of lactation may ensue, and this is costly in terms of the ability to obtain sufficient resources and protecting oneself from harm. There is also the possibility that the relationship will dissolve following pregnancy and the woman may be left to raise a child without the father’s support ( Koehn and Jonason, 2018 ).

Pair-Bonding

Romantic love serves a pair-bonding function ( Fletcher et al., 2015 ). Pair bonding is both a process and a sate characterized by the formation of “enduring, selective attachments between sexual partners” ( Young et al., 2011 , p. 1). It differs from established pair-bonds and the neural characteristics of people experiencing romantic love differ somewhat from what is associated with longer-term pair-bonds (see Acevedo et al., 2012 , for distinction). Evolutionarily, when sex more often led to pregnancy, this pair-bonding would occur in the context of pregnancy and childbirth (although it is unclear if romantic love can exist at the same time as mother-infant bonding). This is still the case in many parts of the world. This is one possible reason for the duration of reciprocated romantic love to be between 18 months and 3 years ( Tennov, 1979 ) when not interrupted by childbirth. The intensity of specific neural activity in people experiencing romantic love is associated with relationship maintenance ( Xu et al., 2012a ).

Romantic love can establish long-term pair-bonds. In both sexes, romantic love promotes the provision of psychological and emotional resources ( Buss, 2019 ) as well as other types of caregiving ( Fletcher et al., 2015 ). It promotes relationship exclusivity through fidelity, jealousy, and mate-guarding ( Buss, 2019 ). Both sexes engage in additional mate retention tactics such as vigilance, mate concealment, monopolization of time, resource display, love and care, or sexual inducements ( Buss et al., 2008 ). Romantic love also promotes the sharing of other resources such as food or money. This benefit for women would have been, and often continues to be, greatest during times of lactation (see Marlowe, 2003 ; Quinlan, 2008 ). Both sexes can also benefit reputationally, as being in a relationship with a high mate value individual confers status, and individuals who are married or in a relationship are viewed more favorably than single people ( DePaulo and Morris, 2006 ). Men experiencing romantic love engage in actions that lead to successful reproductive outcomes ( Buss, 2019 ), such as protecting partners from physical harm. Men also engage in parenting ( Geary et al., 2004 ; Bribiescas et al., 2012 ), which could potentially result in increased offspring survival ( Fletcher et al., 2015 ).

When people are experiencing romantic love they are usually, but not always, interested in pursuing a “long-term mating strategy.” A long-term mating strategy is one that involves commitment, pair-bonding, and the parental investment (if children result) of both partners ( Buss, 2006 ). This contrasts with short-term mating strategies that do not often require public commitment, pair-bonding, and parental investment of the father ( Buss and Schmitt, 1993 ). Pair-bonding is characteristic of a long-term mating strategy.

The concept of romantic love serving as a commitment device is relevant to pair-bonding, as are the concepts of fitness interdependence ( Buss, 2019 ) and self-expansion. Fitness interdependence is the degree to which two people influence each other’s success in replicating their genes ( Aktipis et al., 2018 ). Romantic love binds two individuals together so that the potential reproductive success of one person is contingent upon the success of the other. The self-expansion model suggests that “people seek to expand their potential efficacy to increase their ability to accomplish goals” and that “one way people seek to expand the self is through close relationships, because in a close relationship the other’s resources, perspectives, and identities are experienced, to some extent, as one’s own” ( Aron and Tomlinson, 2019 , p. 2). Fitness interdependence and self-expansion can be increased in people experiencing romantic love.

There are substantial costs associated with pair-bonding ( Kushnick, 2016 ; Klug, 2018 ). Both sexes are potentially missing out on long-term mating opportunities with other suitable mates and are more restricted in terms of short-term mating opportunities ( Geary et al., 2004 ). There is a potential for damage to an individual’s reputation if they are in a relationship with a low mate value individual ( Buss, 2016 ). Both sexes share resources. Pair-bonding is associated with a reduction in the size of an individual’s support network ( Burton-Chellew and Dunbar, 2015 ). Jealousy can have negative effects upon a relationship ( Buss, 2000 , 2019 ; Hatfield et al., 2016 ) and there is a potential for emotional or physical harm arising from a relationship. People sometimes engage in homicide of their current or former partners in response to infidelity, or as a result of jealousy or a breakup ( Buss, 2000 , 2019 ; Shackelford et al., 2003 ). Some women engage in this behavior, but it is predominately a male behavior, when it occurs ( Buss, 2019 ). Stalking can occur following a breakup ( Spitzberg and Cupach, 2003 ; Buss, 2019 ) or, more generally, as a result of romantic love ( Marazziti et al., 2015 ). There is the potential for grief or depression symptoms following the breakup of a relationship ( Verhallen et al., 2019 ). Changing living arrangements, dividing up resources, and legal costs could all be necessary following the dissolution of a pair-bond ( Bear and Rand, 2019 ). Sex-specific costs include sexual obligations to a partner from women and parental investment by men ( Geary et al., 2004 ; Luoto, 2019a ).

While there is evidence that successful pair-bonding is associated with better health and survival ( Fletcher et al., 2015 ), there is little evidence showing that romantic love is associated with good health. Falling in love is associated with alteration in immune cell gene regulation in young women ( Murray et al., 2019 ). Specifically, falling in love is associated with genetic changes that could potentially result in an up-regulation of immune responses to viruses.

Experiencing romantic love for a recently gained partner is associated with the “active/elated” symptoms of hypomania ( Brand et al., 2007 , 2015 ). These symptoms are considered as favorable, “bright side” symptoms and contrast with unfavorable “dark side” symptoms such as disinhibition/stimulation-seeking and irritable/erratic dimensions ( Brand et al., 2015 ). Despite their association with hypomania, the favorable nature of these symptoms in romantic love may be a sign of good physical and mental health because higher hypomanic scores have been associated with higher “mental toughness,” increased physical activity, lower symptoms of depression, and lower sleep complaints ( Jahangard et al., 2017 ). Additionally, falling in love with a partner is sometimes associated with a reduction in depressive symptoms ( Bajoghli et al., 2013 , 2017 ). A reduction in the number of sexual partners could result in a decreased risk of sexually transmitted infections. There is evidence that romantic love might sometimes be associated with improved sleep quality ( Brand et al., 2007 ; Bajoghli et al., 2014 ).

There are some health-related costs associated with romantic love for both sexes. Despite a reduced risk of sexually transmitted infections being a benefit of romantic love, engaging in sexual activity at all may represent an increased risk of sexually transmitted infection, resulting in a cost to some ( Buss, 2016 ; Koehn and Jonason, 2018 ). Infertility from sexually transmitted infections is possible among women ( Koehn and Jonason, 2018 ). Disinhibited/stimulation-seeking and irritable/erratic, depressed, and anxious mood are sometimes features of romantic love ( Wang and Nguyen, 1995 ; Bajoghli et al., 2013 , 2014 , 2017 ; Brand et al., 2015 ; Kuula et al., 2020 ). In the face of repeated unrewarding efforts or adverse events in the courtship process, depressed or anxious mood could result ( Nettle and Bateson, 2012 ). Romantic rejection can result in a major depressive episode or even suicide (see Rantala et al., 2018 ). Despite evidence of improved sleep quality in people experiencing romantic love in some studies ( Brand et al., 2007 ; Bajoghli et al., 2014 ), one study ( Kuula et al., 2020 ) found poorer sleep quality, later sleep timing, and shorter sleep duration (one feature commonly found in studies relied upon to suggest a sleep quality benefit of romantic love) in adolescent girls experiencing romantic love. This suggests that altered sleep may in fact be a detrimental cost in some people experiencing romantic love. Women have the added risk of birth-related complications and death, which has been common in humans until recently in developed countries ( Goldenberg and McClure, 2011 ).

Selective Pressures

The literature contains three interesting theories of possible selective pressures for romantic love. They are framed in the context of promoting the evolution of pair-bonds, but as will be detailed below, the evolution of pair bonds and romantic love are likely to be inexorably linked. All three theories relate to the provision of resources by males to females. The first theory is that pair-bonds and romantic love may have emerged prior to 4 million years ago when bipedalism emerged and hominins moved into the woodlands and savannahs of our ancestral homelands (see Fisher et al., 2016 ). The need for mothers to carry infants in their arms may have driven them to select partners that were wired for pair-bonds which was associated with provisioning, defense, and other forms of support.

The second theory is that biparental care was a driving force in the emergence of long-term mating strategies ( Conroy-Beam et al., 2015 ). A game theoretical approach contends that females selecting males that were wired for pair-bonds directly increased the chances of offspring survival through the provisioning of tangible and intangible resources to the female and offspring. If biparental care was a driving force in the formation of pair-bonds in humans, it would be a uniquely human pressure, as biparental care has been generally identified as a consequence, rather than a cause, of pair-bonds in mammals ( Opie et al., 2013 ; Lukas and Clutton-Brock, 2013 ). This theory also has to contend with the fact that father presence is often not associated with better offspring survival in societies with little access to health care or contraception (see Fletcher et al., 2015 ).

The third theory is that a need for increased fecundity drove the selection of pair-bonds ( Conroy-Beam et al., 2015 ). Periods of malnutrition cause decreased fecundity. Once again, a game theoretical approach suggests that the selection of males that were wired for pair-bonds, which is associated with provisioning of females, increased the caloric intake of females over prolonged periods of time and, in turn, increased fecundity. This hypothesis is appealing because this selective pressure could have been present at any stage among the four hypotheses we propose for the emergence of pair-bonds in a section below.

Romantic Love Is a Complex Suite of Adaptations and By-Products

In evolutionary psychology, an adaptation is “…an inherited and reliably developing characteristic that came into existence as a feature of a species through natural selection because it helped to directly or indirectly facilitate reproduction during the period of its evolution” ( Buss et al., 1998 , p. 535; see also Williams, 2019 ). This approach is based, rightly, on the difficulty of testing hypotheses about the adaptive benefits of traits in ancestral environments. There is an equally valid approach, however, adopted by behavioral ecologists, that views current utility of adaptations as evidence that can be extrapolated to the past ( Fox and Westneat, 2010 ). One definition that has arisen from this approach is that “[a]n adaptation is a phenotypic variant that results in the highest fitness among a specified set of variants in a given environment” ( Reeve and Sherman, 1993 , p. 9).

Taken together, these two approaches to adaptation support the view that romantic love is a “complex suite of adaptations” ( Buss, 2019 , p. 42). The numerous mechanisms recruited in romantic love, the large number of psychological characteristics, and the multiple functions it serves suggest that romantic love may be an amalgamation of numerous adaptations that respond to a variety of adaptive challenges. However, while romantic love may comprise several inter-related adaptations, this does not preclude the possibility that some components are by-products. A by-product is a trait that evolved “not because it was selectively advantageous, but because it was inextricably linked…to another trait that was reproductively advantageous” ( Andrews et al., 2002 , p. 48).

Health-promoting benefits of romantic love, such as elevated mood, increased sleep quality, and up-regulated immune responses, for example, may be by-products of mood circuitry (see Nettle and Bateson, 2012 ; D’Acquisto, 2017 ; Jahangard et al., 2017 ) or other mechanisms, even though they offer some survival or reproductive advantage. Elevated mood, better sleep quality, and an associated up-regulated immune system probably evolved prior to the emergence of romantic love (see Flajnik and Kasahara, 2010 ; Loonen and Ivanova, 2015 ). As a result, it might be prudent to contend that romantic love is a complex suite of adaptations and by-products.

Further, while the evidence points to romantic love as a suite of adaptations and by-products, it is not adaptive in every context. Romantic love continues to have its reproduction-promoting functions in the modern world in some circumstances, either by immediately promoting reproduction, or indirectly promoting reproduction via the formation of romantic relationships, the members of which later reproduce. To that extent, romantic love is sometimes adaptive (see Laland and Brown, 2011 , for distinction between “adaptation” and “adaptive” and lists of benefits, above, for examples of how romantic love can be adaptive). There are circumstances when romantic love may be maladaptive, however, as is evidenced by the substantial fitness-relevant costs of romantic love detailed above. Cogent examples of this are when a loved one is already in a committed relationship or otherwise not interested, when an individual engages in obsessive pursuit that can have social or even legal ramifications, or when violence ensues.

When applied to romantic love, the fourth of Tinbergen’s (1963) four questions asks, “What is the evolutionary history of romantic love?” Phylogenetic explanations focus on the origin and maintenance of a trait in historical evolutionary terms ( Tinbergen, 1963 ; Bateson and Laland, 2013 ). They put a biological trait in a comparative perspective by focusing on the presence or absence of the trait in closely, and sometimes more distantly, related species. In this section, we describe the theory of independent emotion systems and articulate a theory of co-opting mother-infant bonding mechanisms. We examine the primitive structures related to romantic love that arose in our mammalian evolutionary past and were restructured in pair-bonded species. We also examine the particular history of pair-bonds, and thus romantic love, in hominin evolution, with a comparison to other species of primates, especially apes. Finally, we examine the effect of gene-cultural evolutionary issues with regard to romantic love.

Independent Emotion Systems

Fisher’s ( 1998 , 2000 , see also Fisher et al., 2002 ) evolutionary theory of independent emotions systems delineates sex drive (lust), attraction (romantic love), and attachment (pair-bonds). Sex drive is primarily associated with estrogens and androgens and serves to motivate individuals to engage in sexual activity, generally. Attraction is primarily associated with the catecholamines (i.e., dopamine and norepinephrine), phenylethylamine, and serotonin and serves to focus efforts on preferred mating partners. Attachment is primarily associated with oxytocin and vasopressin and serves to enable individuals to engage in positive social behaviors and connections of a sufficient length of time to satisfy species-specific parenting approaches ( Fisher, 1998 ). Sex drive relates most to the sex function of romantic love, attraction to the mate choice and courtship functions, and attachment to the pair-bonding function. Romantic love shares similarities with the ‘courtship attraction system’ found in many mammals ( Fisher et al., 2006 ).

Co-opting Mother Infant Bonding Mechanisms

While the theory of independent emotion systems ( Fisher, 1998 , 2000 ; Fisher et al., 2002 ) has been the predominate theoretical account of the evolution of romantic love for more 20 years, comparative studies, imaging studies, and assessments of psychological characteristics have raised the possibility of a complimentary evolutionary theory, that of co-opting mother-infant bonding mechanisms. Literature on romantic love, maternal love (of which mother-infant bonding is a part), mother–infant bonding, and pair-bonding ( Bartels and Zeki, 2004 ; Ortigue et al., 2010 ; Numan and Young, 2016 ; Walum and Young, 2018 ) suggests romantic love may have evolved by co-opting mother-infant bonding mechanisms. Co-option is an evolutionary process whereby a trait (e.g., mechanism, morphology, behavior) is repurposed – that is, it serves a different function to that which it originally served (see McLennan, 2008 ).

Animal research, focusing on mammals, and involving, monogamous prairie voles, finds substantial similarities between mother-infant bonding mechanisms and pair-bonding mechanisms ( Numan and Young, 2016 ). “[A]mygdala and nucleus accumbens–ventral pallidum (NA–VP) circuits are involved in both types of bond formation, and dopamine and oxytocin actions within NA appear to promote the synaptic plasticity that allows either infant or mating partner stimuli to persistently activate NA–VP attraction circuits, leading to an enduring social attraction and bonding” ( Numan and Young, 2016 , p. 98). Some of these circuits do not appear to be involved in human romantic love, but there are other similarities that support a theory of co-opting mother-infant bonding in humans.

Several brain regions implicated in romantic love overlap precisely with that involved in maternal love. This includes activity in numerous regions that are associated with a high density of oxytocin and vasopressin receptors ( Bartels and Zeki, 2000 , 2004 ) although it should be noted that in the study that asserts this, participants included mothers experiencing maternal love beyond the mother-infant bonding stage. A meta-analysis of love also found romantic and maternal love shared activity in dopamine-rich areas ( Ortigue et al., 2010 ). Almost nothing is known about the mechanisms regulating the infant side of mother-infant bonding. However, some inferences have been made from animal models which suggest that the mechanisms may be similar to those regulating the maternal side, but without involvement of the amygdala (see Sullivan et al., 2011 , for review).

There are substantial psychological similarities between romantic love and early parental love, of which mother–infant bonding is a part. Extreme similarities exist between romantic love and early parental love in the domains of altered mental state, longing for reciprocity, idealization of the other, and dichotomous resolution of the establishment of intimate mutually satisfying reciprocal patterns of interaction usually marked by a culturally defined ritual ( Leckman and Mayes, 1999 ). Similar trajectories of preoccupation in romantic love and parental love also exist. In romantic love, preoccupation increases through the courtship phase and peaks at the point of reciprocity where preoccupation begins to slowly diminish. In parental love, preoccupation increases throughout pregnancy and peaks at the point of birth where preoccupation begins to diminish.

Mammalian Antecedents

Romantic love in humans is caused by physiological mechanisms whose evolutionary roots were planted in our early mammalian ancestors. These evolutionary roots provided the raw materials that were fleshed out, in evolutionary time, to form the basis of a wide range of social behaviors in mammals, including those related to sex drive, mate choice, and attachment ( Fisher, 1998 , 2000 ; Fisher et al., 2002 ; Broad et al., 2006 ; Carter and Perkeybile, 2018 ; Curley and Keverne, 2005 ; Fisher et al., 2006 ; Fischer et al., 2019 ; Johnson and Young, 2015 ; Numan and Young, 2016 ; Porges, 1998 ). Romantic love may have evolved after the neural circuitry associated with mate choice became populated by oxytocin receptors which played a role in the evolution of enduring social attraction and pair-bond formation (see Numan and Young, 2016 ). “[P]air bonding is the evolutionary antecedent of romantic love and…the pair bond is an essential element of romantic love” ( Walum and Young, 2018 , p. 12).

Examining the similarities between the neurobiological and endocrinological mechanisms involved in mother-infant bonding and pair-bonding in mammals, it becomes apparent that the maternal functions of this suite of adaptations arose deep in the evolutionary history of mammals ( Numan and Young, 2016 ). Their derived, pair-bonding functions would have arisen later in a very small number of species (only 3–5% pair-bond). As such, the neural circuitry and other proximate mechanisms involved in mother-infant bonding in mammals “may have provided a primordial neural scaffold upon which other types of strong social bonds, such as pair bonds, have been built” ( Numan and Young, 2016 , p. 99). We are, thus, on reasonably solid ground to posit evolutionary trajectories of romantic love. Figure 1 presents information and hypotheses about the evolutionary history of romantic love. Evolutionary trajectories of romantic love start with the ancestral mammalian mother–infant bonding mechanisms and culminate in their co-option and modification for pair-bonding in several mammalian lineages ( Numan and Young, 2016 ). Human romantic love results from one of these trajectories. In another trajectory—the one that includes pair-bonding prairie voles ( Microtus ochrogaster )—we know quite a lot about the functioning of oxytocin, vasopressin, and dopamine in facilitating pair-bonding (e.g., Carter and Getz, 1993 ; Carter and Perkeybile, 2018 ; Walum and Young, 2018 ). Although these derived changes to the primitive mammalian machinery may not be the direct evolutionary antecedents of those at work in humans (they are, rather, the product of parallel evolution), they provide a window into how basic machinery can be modified to affect those ends. One substantive difference appears to be the relative importance of the hormonal drivers in the smaller species, and the dopamine-related ones in humans ( Broad et al., 2006 ; Fisher et al., 2016 ).

Phylogenetic relationships among select mammal species that pair-bond.

Pair-Bonds in Primates

Humans are members of the primate superfamily Anthropoidea, amongst whom there is great diversity in social systems, and whose ancestral state likely included complex group-based social relationships ( Kay et al., 1997 ; Shultz and Dunbar, 2007 ). This would have included long-term association between unrelated males and females—which is a far cry from the solitary system that is modal and ancestral for mammals ( Lukas and Clutton-Brock, 2013 ; Opie et al., 2013 ). There are even some members of this lineage who have evolved pair-bonds, such as the marmosets and tamarins (Callitrichidae), and gibbons (Hylobatidae). The similarities between these species and humans in terms of the adaptive suite related to pair-bonds, like the similarities between humans and voles, are due to convergent/parallel evolution ( French et al., 2018 ).

Our closest living relatives are the common chimpanzee ( Pan troglodytes ) and bonobo ( Pan paniscus ) with whom we share a common ancestor just 5–8 million years ago. While bonobos are alluring due to their free-willed sexual nature, common chimpanzees provide a better glimpse into the behavior of our direct ancestors. Although the common chimpanzee mating system is defined as promiscuous, there are, in fact, three forms of common chimpanzee mating tactics ( Morin, 1993 ). The first two—possessive mating and consortships—involve some of the characteristics we associate with romantic love, such as a more-than-fleeting association and mate guarding, but they are much rarer than the third type, opportunistic mating. The comparison of chimpanzees and humans, thus, suggests that one possible hypothesis for the emergence of romantic love is that it originated in their common ancestor (H1 in Figure 1 ). Alternatively, it might be that the common ancestor had an adaptive repertoire that was primed for its emergence when the requisite socioecological context arose. In this way, the evolution of romantic love from chimp-like mating is similar to the evolution of human culture from chimp-like culture.

For some, the origin of romantic love was more likely to have fallen somewhere on our side of the human–chimpanzee split (e.g., Fisher et al., 2016 ). Even so, we are left with the difficulty of pinpointing exactly when it arose—attributable to there being only one extant hominin species from amongst the many that have existed ( Pigliucci and Kaplan, 2006 ) and the lack of direct fossil evidence for romantic love. If we accept the conventional view that romantic love evolved to facilitate pair-bonding, then we can search for clues about the evolution of the former by tracing the evolution of the latter ( Fletcher et al., 2015 ). A transition from ape-like to human-like sexual behavior in our lineage may have pre-dated the emergence of the genus Homo ( Lovejoy, 1981 )—and, thus, we have a second hypothesis (H2 in Figure 1 ). A comparison of sexual dimorphism in Australopithecus and early genus Homo , however, suggests a third hypothesis—that it arose after their emergence (H3 in Figure 1 ). Several lines of evidence suggest that the earliest members of our species, Homo sapiens , pair-bonded but were not necessarily monogamous. Based on an examination of the distribution of mating systems in modern, small-scale human societies and three correlates of primate mating systems ( Dixson, 2009 ), it is possible to conclude that pair-bonds are a “ubiquitous” feature of human mating that can manifest through polygyny or polyandry, but most commonly occur in the form of serial monogamy ( Schacht and Kramer, 2019 ). The final hypothesis, thus, is that romantic love is the unique domain of our species (H4 in Figure 1 ).

The transition to mostly monogamous and some polygynous groupings could have had a transitional phase where polygynous groupings were the norm ( Chapais, 2008 , 2013 ). Pair-bonds may have arisen from a complex interaction between the fitness benefits and costs of mating and parental care ( Quinlan, 2008 ). The transition from ape-like promiscuity to human pair-bonds may have been driven by the provision of females by low-ranking males ( Gavrilets, 2012 ). The direct benefits for females was the food provided, for the males, the mating opportunity. This may have led to selection for males that were less aggressive and more prosocial. The female mate-choice mechanism is a distinct possibility for explaining human self-domestication ( Gleeson and Kushnick, 2018 ).

Gene-Culture Coevolution

Romantic love is a universal or near-universal feature in human societies ( Jankowiak and Fischer, 1992 ; Gottschall and Nordlund, 2006 ; Jankowiak and Paladino, 2008 ; Fletcher et al., 2015 ; Buss, 2019 ; Sorokowski et al., 2020 ). A small number of genetic correlation studies show that there are a number of genes associated with romantic love ( Emanuele et al., 2007 ; Murray et al., 2019 ; Acevedo et al., 2020 ). Other insights into the genetic evolution of romantic love can be garnered from elsewhere, however. For example, life history theory provides insight into ethnic or geographical variation in romantic love and its role in providing sexual access by women.

Romantic love is among the most common reasons female adolescents give for having sex ( Ozer et al., 2003 ). A “slow” life history strategy is associated with eros more than other loving styles ( Marzec and Łukasik, 2017 ). Psychopathology associated with impulsivity is a feature of a “fast” life history strategy, as is promiscuous sexuality ( Del Giudice, 2016 ). Greater impulsivity is associated with a reduced likelihood of giving romantic love as a reason for having sex among adolescent females ( Dawson et al., 2008 ).

As a result, genetic determinants of life history strategies (e.g., Figueredo et al., 2004 ) may influence the occurrence of romantic love. National scores on the life history strategy genetic factor index correlate with adolescent fertility rates indicating that genetic predictors of a fast life history are associated with higher rates of adolescent pregnancy ( Luoto, 2019b ). This ethnic or geographical variation in the genetic determinants of life history strategies may also represent ethnic or geographic variation in the genetic determinants and reproductive relevance of romantic love.

In addition to this, cultural factors may have affected the role of romantic love in mating and marriage decisions—and this has implications for understanding the evolution of romantic love ( Fletcher et al., 2015 ). Arranged marriages are the norm in 80% of 200 forager societies from the Ethnographic Atlas ( Apostolou, 2007 ). Phylogenetic methods to reconstruct the ancestral marriage patterns of our species using the same data found that there were likely marriage transactions (brideprice or brideservice) but only a limited amount of polygyny ( Walker et al., 2011 ). While the ancestral state for arranged marriages was not definitive, arranged marriages were likely present around 50 thousand years ago, when our ancestors expanded their range beyond Africa. So, despite romantic love being viewed as an important component of marriage and mating, it may have played a role of decreasing importance in the recent evolutionary history of our species. Arranged marriages may have limited the role of female mate choice in intersexual selection ( Apostolou, 2007 ). Further, despite romantic love’s decreased role in courtship and marriage, it may have continued to serve a role in facilitating pair-bonding as romantic love can develop even in the arranged-marriage context. The role of romantic love in facilitating mate choice, courtship, and marriage may now be increasing with the decline and modification of arranged marriages in many parts of the world (e.g., Allendorf and Pandian, 2016 ). This may be the result of the increasing sexual equality of women (e.g., de Munck and Korotayev, 1999 ).

Romantic love is a complex and multifaceted aspect of human biology and psychology. Our approach in this review has been to highlight how Tinbergen’s (1963) “four questions” can help us to synthesize the important strands related to the mechanisms, development, fitness-relevant functions, and evolutionary history of this phenomenon. Here, we synthesize what this review has presented in each level of explanation and suggest what this indicates about other levels of explanation. We then highlight some gaps in our knowledge that could be filled with future research and present a new ethologically informed working definition of romantic love.

What Do Tinbergen’s Four Questions Tell Us?

One of the benefits of using Tinbergen’s four questions as a framework to describe a complex trait such as romantic love is its ability for one level of explanation to provide insights into the other level of explanation (see Tinbergen, 1963 ; Bateson and Laland, 2013 ; Zietsch et al., 2020 ). In particular, an understanding of the proximate causes of romantic love has provided insights into the functions and phylogeny of romantic love although an understanding of the ultimate level of explanation provides some insights into the mechanisms of romantic love.

Multiple mechanistic systems involved in romantic love suggests it may serve multiple functions and may be a suite of adaptations and by-products rather than a single adaptation. We found that romantic love is associated with activity in a number of neural systems: reward and motivation, emotions, sexual desire and arousal, and social cognition. It is also associated with activity in higher-order cortical brain areas that are involved in attention, memory, mental associations, and self-representation. We also found that romantic love is associated with a number of endocrine systems: sex hormones, serotonin, dopamine, oxytocin, cortisol, and nerve growth factor. This is consistent with our position that romantic love serves mate choice, courtship, sex, and pair-bonding functions. Reward and motivation system activity may be particularly involved in the mate choice function of romantic love. Cortisol may be particularly indicative of the courtship function of romantic love, which overlaps with pair-bonding. Neural areas associated with sexual desire and arousal and the activity of sex hormones may play a particular role in the sex function. Finally, reward and motivation regions of the brain (rich with oxytocin receptors) and activity of the oxytocin system may play a particular role in the pair-bonding function of romantic love. Our understanding of the biological mechanisms that cause romantic love supports our description of romantic love’s functions.

Mechanistic similarities between romantic love and mother-infant bonding suggest that romantic love may have evolved by co-opting mother-infant bonding mechanisms. This articulates one hypothesis about the evolutionary history of romantic love that complements the predominate theory of independent emotion systems ( Fisher, 1998 , 2000 ; Fisher et al., 2002 ). This is supported by the psychological similarities between romantic love and early parental love.

Evidence of substantial activity of oxytocin receptor rich brain regions and the oxytocin endocrine system in romantic love lends weight to the position that romantic love only evolved after the neural circuitry associated with mate choice, specifically, regions of the mesolimbic reward pathway and dopamine rich areas, became populated by oxytocin receptors specifically receptive to stimuli from mating partners. That played a role in the evolution of enduring social attraction and pair-bond formation ( Numan and Young, 2016 ). This supports our claim that romantic love probably evolved in conjunction with pair-bonds in humans. As a result, we are bolstered when we contend that romantic love emerged relatively recently in the history of humans.

The duration of romantic love also raises questions about the functions of romantic love. It has been said that the psychological features of romantic love can last from 18 months to 3 years in reciprocated romantic love. However, in our evolutionary history, romantic love would have usually occurred in the context of pregnancy and child birth. Mother-infant bonding becomes active around the time of childbirth. We are not aware of any research that has investigated whether romantic love can occur at the same time as mother-infant bonding or whether it must subside for mother-infant bonding to become active. Answering this question would elucidate if the functions of romantic love extinguish once reproduction has been successful. The existence of long-term romantic love also raises questions about the functions of romantic love. It has been posited that long-term romantic love is “part of a broad mammalian strategy for reproduction and long-term attachment” ( Acevedo et al., 2020 , p. 1). This may indicate that long-term romantic love serves similar functions to romantic love that lasts a shorter period of time.

Just as the multiple biological mechanisms involved in romantic love suggests a variety of functions, the functions of romantic love specified in our review suggests specific biological mechanisms are involved. As outlined above, specific functions may be associated with specific mechanisms and this should be an area of targeted research.

The possibility of romantic love evolving by co-opting mother-infant bonding mechanisms raises a number of possibilities in relation to the proximate causes of romantic love. It suggests that social activity associated with mother–infant bonding (e.g., filling of needs, specific cues) may be particularly important precursors to, or features of, romantic love. It suggests that many of the genes and polymorphisms involved in causing romantic love may have been present in mammals since the emergence of mother–infant bonding, making comparative animal research using mammals relevant. It also suggests that further research into shared neural activity between romantic love and mother–infant bonding is warranted.

We contend that romantic love probably emerged in conjunction with pair-bonds in humans or human ancestors. As such, further information about the similarities and differences between romantic love (pair-bonding) and companionate love (established pair-bonds) is needed. In particular, information about any role of the mesolimbic pathway (see Loth and Donaldson, 2021 ) or regions associated with sexual desire in companionate love would help to shed light on the evolutionary history of pair-bonding and pair-bonds. Specifically, this could shed light on if, as has been suggested (see Walum and Young, 2018 ), romantic love and pair-bonds are inextricably linked.

Areas of Future Research

One issue with research into the mechanisms of romantic love is that it has, with some exceptions (e.g., Fisher et al., 2010 ), utilized samples of people experiencing romantic love who are in a relationship with their loved one. Romantic love serves a mate choice and courtship function, and as a result, a large proportion of people experiencing romantic love are not in a relationship with their loved one (e.g., Bringle et al., 2013 ). A small number of studies have directly investigated unrequited love (e.g., Tennov, 1979 ; Baumeister et al., 1993 ; Hill et al., 1997 ; Aron et al., 1998 ; Bringle et al., 2013 ), but none of these investigated the mechanisms that cause romantic love. Studying such people might identify the specific contributions of particular mechanisms to particular functions. For example, the mechanisms associated with the pair-bonding function of romantic love may not be active in individuals who are engaging in courtship and the mechanisms involved in courtship may not be present in lovers who are already in a relationship with their loved one. Research would benefit from considering the mechanisms that underlie related psychopathologies and it would be useful to understand the relationship between mate preferences and romantic love.

Molecular genetics research, such as that undertaken by Acevedo et al. (2020) , could further identify contributions of genes in people experiencing romantic love. Resting state fMRI provide an opportunity to investigate networks characteristic of psychopathology related to romantic love. Research should investigate the automatic/internal emotional regulatory network and the volitional/external regulatory network associated with mania/hypomania in people experiencing romantic love. Further research is required into the endocrinology of romantic love. In particular, further research is needed into the role of opioids, corticotropin-releasing factor, glutamate, acetylcholine, and vasopressin in romantic love. Efforts should be made to combine psychological and mechanisms research. For example, differences in neural or endocrine activity may be present in people experiencing romantic love who display elevated symptoms of depression compared to those who display reduced symptoms. As a result, neuroimaging and endocrinological studies could categorize people experiencing romantic love according to their levels of depression or type of hypomanic symptoms.

Given the large number of fMRI studies, interpreting the neuroimaging literature can be overwhelming. It has been nearly 10 years since the last meta-analysis of fMRI studies including romantic love. It is time for another one that focuses solely on romantic love. There is also a pressing need to attempt to replicate and extend endocrine studies and to specifically investigate the oxytocin system in people experiencing romantic love using validated measures of romantic love. As with many areas of psychological research ( Henrich et al., 2010 ), and specifically in areas related to mating psychology ( Apicella et al., 2019 ; Scelza et al., 2020 ), there is a pressing need to ensure that samples used in research are not exclusively Western, educated, industrialized, rich, and democratic.

Limited ontogeny research has elucidated the mechanisms causing romantic love across the lifespan. The literature that has (e.g., Luoto, 2019a ), has focused on mate choice, rather than romantic love, per se . We know nothing about the neurobiology or endocrinology of romantic love in children or about the endocrinology of long-term romantic love. It would be useful to investigate how the functions of romantic love differ according to age of individuals or the duration of romantic love. Internal and external factors influence romantic love, although there has been surprisingly little research into this topic. It would be prudent to continue to develop a more detailed understanding of the factors that lead to romantic love (e.g., Riela et al., 2010 , 2017 ). It would be useful to better understand the relationship between attachment styles and romantic love. Research should investigate if romantic love can occur at the same time as mother-infant bonding, or if they are mutually exclusive states.

Research into the functions of romantic love is sparse. There is a need for clear, evidence-informed definitions and descriptions of each of the functions of romantic love. It is likely that different mechanisms moderate different functions, and research should attempt to determine the contribution of specific genetic, neural, and endocrine activity to each individual function (see Zietsch et al., 2020 ). The advent of contraception and the adoption of family planning strategies means romantic love now serves more of a sex function than a pregnancy function in some environments. This is particularly the case early in a relationship. Pregnancy may become a feature as a relationship progresses and the fitness consequences of romantic love need to be investigated. Romantic love’s role as a suite of adaptations and by-products should be investigated. There is theoretical support for the notion that romantic love serves a health-promoting function (e.g., Esch and Stefano, 2005 ); however, there is a limited number of studies demonstrating a health-promoting effect of romantic love.

The relative infancy of genetic research, the lack of a clear fossil record, and the small number of species with which comparative analysis can be undertaken, means novel and creative means of investigating the phylogeny of romantic love must be undertaken. There is a need to pin-point the phylogenetic emergence of romantic love and the factors that caused it. To do this, more research into the genetics of romantic love must be conducted, and this should consider the phylogeny of specific genes and polymorphisms (e.g., Acevedo et al., 2020 ; see also Walum and Young, 2018 ). Efforts to assess the contribution of sexual selection to the evolution of romantic love are warranted. Studies of newly discovered fossils can help to identify shifts in sexual dimorphism that are indicative of pair-bonds. Further observational and experimental research into romantic love in hunter-gatherer tribes could tell us more about how romantic love functioned in our evolutionary history. Comparative research still has much to contribute. Research should explore the possibility that initial changes to the ancestral mammalian physiology that led directly to human romantic love arose in response to selection on both mating and non-mating-related behavior, such as pro-sociality (e.g., Barron and Hare, 2020 ; Luoto, 2020 ) or unique aspects of our species’ parenting repertoire. It might be fruitful to further investigate the relationship between romantic love and life history theory (e.g., Olderbak and Figueredo, 2009 ; Marzec and Łukasik, 2017 ). Finally, efforts should be made to elaborate and test the theory that romantic love emerged by co-opting mother–infant bonding mechanisms.

A New Working Definition of Romantic Love

The introduction to this review provided four definitions or descriptions of romantic love. For decades, most definitions ( Hendrick and Hendrick, 1986 ; Sternberg, 1986 ; Hatfield and Rapson, 1993 ) of romantic love have informed research into the cognitive, emotional, and behavioral characteristics of romantic love. The past two decades, however, have seen an increasing focus on the biology of romantic love. Only recently has an evolution-informed definition been proposed ( Fletcher et al., 2015 ). That working definition, however, does not incorporate much of the research that provides insight into the proximate and ultimate causes of romantic love.

We believe that the analytical approach taken in this review has identified sufficient information to justify the development of a new ethologically informed working definition of romantic love. The purpose would be to create an inclusive definition that is useful for researchers in varied disciplines investigating romantic love’s psychological characteristics, genetics, neurobiology, endocrinology, development, fitness-relevant functions, and evolutionary history. It may also be of use to psychologists and psychiatrists attempting to understand the experience and etiology of romantic love in their practice. It should be sufficiently precise and descriptive to both guide and link research. We provide, here, a working definition of romantic love:

• Romantic love is a motivational state typically associated with a desire for long-term mating with a particular individual. It occurs across the lifespan and is associated with distinctive cognitive, emotional, behavioral, social, genetic, neural, and endocrine activity in both sexes. Throughout much of the life course, it serves mate choice, courtship, sex, and pair-bonding functions. It is a suite of adaptations and by-products that arose sometime during the recent evolutionary history of humans.

We situate the study of romantic love within the context of existing human mating literature. Our definition recognizes that romantic love is experienced across the lifetime of an individual, that research has shed light on the social, psychological, genetic, neural, and endocrine characteristics associated with it, and that it occurs in both sexes. Our definition also recognizes that romantic love serves a variety of functions and that these functions may vary across the lifespan. It does not exclude long-term or unrequited romantic love from the definition. Health is not identified as a function of romantic love in our definition despite being considered in our review. If more evidence comes to light, this definition can be amended to incorporate health.

Our definition has similarities and differences with the definition proposed by Fletcher et al. (2015) . This is appropriate given both are informed by evolutionary approaches which differ somewhat. We do not specifically define romantic love as being a commitment device or reference passion, intimacy, and caregiving. In our review, we recognize that romantic love is a commitment device and serves to display commitment and signal fidelity as part of its courtship function. We believe that reference to romantic love’s behavioral activity and courtship and pair-bonding functions sufficiently encapsulate this concept. Sternberg’s (1997) definition of romantic love and Fletcher et al.’s (2015) definition include references to passion and intimacy. Caregiving (e.g., provision of psychological and emotional resources, sharing resources), while associated with pair-bonding, is not sufficiently definitive of romantic love using Tinbergen’s four questions as a framework to include in our definition.

We do not reference the universality of romantic love. While some experts assert its universality (e.g., Fletcher et al., 2015 ; Buss, 2019 ), we believe that the finding of Jankowiak and Fischer (1992) leaves enough uncertainty for it to be prudent to omit this aspect from our definition. Their research has found no evidence of romantic love in fifteen cultures (see Jankowiak and Paladino, 2008 , for update to the original investigation) although this is probably the result of lack of data rather than evidence to the contrary. Once this matter is settled, which could be achieved by further investigating those societies where no evidence of romantic love was found, the definition can be amended. Fletcher et al. (2015) state that romantic love is associated with pair-bonds. We do the same by stating that pair-bonding is one of the functions of romantic love.

We also do not make specific reference to romantic love suppressing the search for mates. We recognize this as a cost in our review, but do not believe that this is so definitive of romantic love to include in our definition. Rather, we believe that our reference to “behavioral” activity and the “mate choice” function of romantic love in our definition sufficiently accommodates this feature. Our definition provides more detail than that provided by Fletcher et al. (2015) by including elements derived from substantial research into the mechanisms, ontogeny, functions, and phylogeny of romantic love. Like the Fletcher et al. (2015) definition, our definition recognizes that romantic love has distinct psychological characteristics and that we know about some of the proximate mechanisms that regulate it. However, as explained above, we do not include reference to the health-promoting effects of romantic love.

As more information about romantic love is gathered, we anticipate the definition to develop. However, we believe that this definition is an improvement upon previous definitions and adequately captures what is currently known about romantic love’s proximate and ultimate causes. It would be useful for researchers investigating romantic love from myriad perspectives. This definition should be critiqued and improved, and we welcome any such efforts from researchers and theorists across the spectrum of academic disciplines.

Our review provides a comprehensive account of the phenomenon known as romantic love. It covers topics such as social precipitants, psychology, genetics, neurobiology, and endocrinology. It provides an account of romantic love across the lifetime of an individual and is the first to propose four discrete reproduction-related functions of romantic love supported in the literature: mate choice, courtship, sex, and pair-bonding. It provides a summary of the benefits and costs of romantic love, outlines possible selective pressures, and posits that it is a complex suite of adaptations and by-products. We propose four potential evolutionary histories of romantic love and introduce the theory of co-opting mother-infant bonding mechanisms. We have identified a number of specific and general areas for future research. Our review suggests a new, ethologically informed working definition of romantic love that synthesizes a broad range of research. The working definition we propose serves to define a complex trait in a way that can both guide and link research from a variety of fields.

Author Contributions

AB conceived the manuscript. AB and GK collaborated on the development of the analytical framework and writing of the manuscript. Both authors approved the final version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We would like to thank the reviewers for comments that helped to improve the manuscript.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpsyg.2021.573123/full#supplementary-material

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Title: a silicon valley love triangle: hiring algorithms, pseudo-science, and the quest for auditability.

Abstract: In this paper, we suggest a systematic approach for developing socio-technical assessment for hiring ADS. We suggest using a matrix to expose underlying assumptions rooted in pseudoscientific essentialized understandings of human nature and capability, and to critically investigate emerging auditing standards and practices that fail to address these assumptions.

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Antioxidants

Often used as a marketing buzzword, learn about the role of antioxidants beyond the hype, and some of the research on health and disease prevention.

Jump to: – What are antioxidants? – Health benefits of antioxidants: what’s the buzz? – Studies of antioxidant supplements and disease prevention – Antioxidants in food – Bottom line on antioxidants and disease prevention

What are antioxidants?

The body’s trillion or so cells face formidable threats, from lack of food to infection with a virus. Another constant threat comes from chemicals called free radicals. In very high levels, they are capable of damaging cells and genetic material. The body generates free radicals as the inevitable byproducts of turning food into energy. Free radicals are also formed after exercising or exposure to cigarette smoke, air pollution, and sunlight. [1]

Free radicals come in many shapes, sizes, and chemical configurations. What they all share is a voracious appetite for electrons, stealing them from any nearby substances that will yield them. This electron theft can radically alter the “loser’s” structure or function. Free radical damage can change the instructions coded in a strand of DNA. It can make a circulating low-density lipoprotein (LDL, sometimes called bad cholesterol) molecule more likely to get trapped in an artery wall. Or it can alter a cell’s membrane, changing the flow of what enters the cell and what leaves it. An excessive chronic amount of free radicals in the body causes a condition called oxidative stress, which may damage cells and lead to chronic diseases. [2]

We aren’t defenseless against free radicals. The body, long used to this relentless attack, makes many molecules that quench free radicals as surely as water douses fire. We also extract free-radical fighters from food. These defenders are labeled “antioxidants.” They work by generously giving electrons to free radicals without turning into electron-scavenging substances themselves. They are also involved in mechanisms that repair DNA and maintain the health of cells.

There are hundreds, probably thousands, of different substances that can act as antioxidants. The most familiar ones are vitamin C , vitamin E , beta-carotene , and other related carotenoids, along with the minerals selenium and manganese. They’re joined by glutathione, coenzyme Q10, lipoic acid, flavonoids, phenols, polyphenols, phytoestrogens, and many more.  Most are naturally occurring, and their presence in food is likely to prevent oxidation or to serve as a natural defense against the local environment.

But using the term “antioxidant” to refer to substances is misleading. It is really a chemical property, namely, the ability to act as an electron donor. Some substances that act as antioxidants in one situation may be pro-oxidants—electron grabbers—in a different situation. Another big misconception is that antioxidants are interchangeable. They aren’t. Each one has unique chemical behaviors and biological properties. They almost certainly evolved as parts of elaborate networks, with each different substance (or family of substances) playing slightly different roles. This means that no single substance can do the work of the whole crowd.

Health benefits of antioxidants: what’s the buzz?

Antioxidants came to public attention in the 1990s, when scientists began to understand that free radical damage was involved in the early stages of artery-clogging atherosclerosis. It was also linked to cancer , vision loss, and a host of other chronic conditions. Some studies showed that people with low intakes of antioxidant-rich fruits and vegetables were at greater risk for developing these chronic conditions than were people who ate plenty of those foods. Clinical trials began testing the impact of single substances in supplement form, especially beta-carotene and vitamin E, as weapons against chronic diseases.

Even before the results of these trials were in, the media and the supplement and food industries began to hype the benefits of “antioxidants.” Frozen berries, green tea, and other foods labeled as being rich in antioxidants began popping up in stores. Supplement makers touted the disease-fighting properties of all sorts of antioxidants.

The research results were mixed, but most did not find the hoped-for benefits. Most research teams reported that vitamin E and other antioxidant supplements didn’t protect against heart disease or cancer. [3] One study even showed that taking beta-carotene supplements actually increased the chances of developing lung cancer in smokers. On the other hand, some trials reported benefits; for example, after 18 years of follow-up, the Physicians’ Health Study found that taking beta-carotene supplements was associated with a modest reduction in the rate of cognitive decline. [4]

These mostly disappointing results haven’t stopped food companies and supplement sellers from banking on antioxidants. Antioxidants are still added to breakfast cereals, sports bars, energy drinks, and other processed foods , and they are promoted as additives that can prevent heart disease, cancer, cataracts, memory loss, and other conditions.

Often the claims have stretched and distorted the data: While it’s true that the package of antioxidants, minerals , fiber , and other substances found naturally in fruits , vegetables , and whole grains helps prevent a variety of chronic diseases , it is unlikely that high doses of antioxidant supplements can accomplish the same feat.

Antioxidant foods hyped to super-status

Antioxidant supplements and disease prevention: little supportive evidence.

Randomized placebo-controlled trials, which can provide the strongest evidence, offer little support that taking vitamin C, vitamin E, beta-carotene, or other single antioxidants provides substantial protection against heart disease, cancer, or other chronic conditions. The results of the largest trials have been mostly negative.

Vitamin E, beta-carotene, and other antioxidants in supplement form aren’t the silver bullet against heart disease and stroke that researchers were hoping for.  A modest effect of vitamin E has been found in some studies but more research is needed.

• In the Women’s Health Study, 39,876 initially healthy women took 600 IU of natural source vitamin E or a placebo every other day for 10 years. At the study’s end, the rates of major cardiovascular events and cancer were no lower among those taking vitamin E than those taking the placebo. However, the trial did observe a significant 24% reduction in total cardiovascular mortality. Although this was not a primary endpoint for the trial, it nevertheless represents an important outcome. [6]
• Earlier large vitamin E trials, conducted among individuals with previously diagnosed coronary disease or at high risk for it, generally showed no benefit. In the Heart Outcomes Prevention Evaluation (HOPE) trial, the rates of major cardiovascular events were essentially the same in the vitamin E (21.5%) and placebo (20.6%) groups, although participants taking vitamin E had higher risks of heart failure and hospitalization for heart failure. [7] In the Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardico (GISSI) trial, the results were mixed but mostly showed no preventive effects after more than three years of treatment with vitamin E among 11,000 heart attack survivors. [8] However, some studies suggest potential benefits among certain subgroups. A recent trial of vitamin E in Israel, for example, showed a marked reduction in coronary heart disease among people with type 2 diabetes who have a common genetic predisposition for greater oxidative stress. [9]
• Beta-carotene, meanwhile, did not provide any protection against heart disease or stroke, as demonstrated by the Physicians’ Health Study. [10]
• What about combinations? In the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI.MAX) study, 13,017 French men and women took a single daily capsule that contained 120 mg vitamin C, 30 mg vitamin E, 6 mg beta-carotene, 100 mcg selenium, and 20 mg zinc, or a placebo, for seven and a half years. The vitamins had no effect on overall rates of cardiovascular disease. [11]
• In the Women’s Antioxidant Cardiovascular Study, vitamin E, vitamin C, and beta-carotene had similar effects as a placebo on myocardial infarction, stroke, coronary revascularization, and cardiovascular death, although there was a modest and significant benefit for vitamin E among women with existing cardiovascular disease. [12]

A 2014 study from the Journal of Respiratory Research found that different isoforms of vitamin E (called tocopherols) had opposing effects on lung function. [13] The study analyzed data from the Coronary Artery Risk Development in Young Adults (CARDIA) cohort and measured serum levels of alpha- and gamma-tocopherol in 4,526 adults. Lung function was tested using spirometric parameters: higher parameters are indicative of increased lung function, while lower parameters are indicative of decreased lung function. The study found that higher serum levels of alpha-tocopherol were associated with higher spirometric parameters and that high serum levels of gamma-tocopherol were associated with lower spirometric parameters. Though the study was observational in nature, it confirmed the mechanistic pathway of alpha- and gamma-tocopherol in mice studies. [14]

When it comes to cancer prevention, the picture remains inconclusive for antioxidant supplements. Few trials have gone on long enough to provide an adequate test for cancer.

• In the long-term Physicians’ Health Study, cancer rates were similar among men taking beta-carotene and among those taking a placebo. [10] Other trials have also largely shown no effect, including HOPE. [7]
• The SU.VI.MAX randomized placebo-controlled trial showed a reduction in cancer risk and all-cause mortality among men taking an antioxidant cocktail (low doses of vitamins C and E, beta-carotene, selenium, and zinc) but no apparent effect in women, possibly because men tended to have low blood levels of beta-carotene and other vitamins at the beginning of the study. [11]
• A randomized trial of selenium in people with skin cancer demonstrated significant reductions in cancer and cancer mortality at various sites, including colon, lung, and prostate. [15]  The effects were strongest among those with low selenium levels at baseline.
• A six-year trial, the Age-Related Eye Disease Study (AREDS), found that a combination of vitamin C, vitamin E, beta-carotene, and zinc offered some protection against the development of advanced age-related macular degeneration, but not cataracts, in people who were at high risk of the disease. [16,17]
• Lutein, a naturally occurring carotenoid found in green, leafy vegetables such as spinach and kale, may protect vision. However, relatively short trials of lutein supplementation for age-related macular degeneration have yielded conflicting findings. [18,19] A follow-up trial to the AREDS, the AREDS2, examined lutein/zeaxanthin supplementation on late age-related macular degeneration (AMD) in men and women for up to five years. [20] It found a favorable but not significant effect of the supplements on AMD.
• A Cochrane review of 19 randomized controlled trials compared antioxidant vitamin/mineral supplements (multivitamin, vitamin E, lutein, zeaxanthin, zinc) with placebo or no intervention in people with AMD. [21] The participants were generally well-nourished. The study found that people taking the vitamins were less likely to progress to late-stage AMD and vision loss. However, the study authors noted that taking lutein and zeaxanthin alone or vitamin E alone did not have a beneficial effect on these eye conditions.
• The Selenium and Vitamin E Cancer Prevention Trial (SELECT) Eye Endpoints Study, which followed 11,267 men for a mean of five years, did not find that vitamin E and selenium supplements, in combination or alone, protected from age-related cataracts. [22]
• The Physicians’ Health Study II, a randomized trial giving 50 mg beta-carotene supplements or a placebo to 5,956 men older than 65 years, found that longer-term supplementation for at least 15 years provided cognitive benefits. [4]
• The Prevention of Alzheimer’s Disease by Vitamin E and Selenium (PREADViSE) trial followed more than 3,700 men ages 60 and older for six years. It did not find that antioxidant supplements of vitamin E or selenium, alone or in combination, protected against dementia compared with a placebo. [23]
• A meta-analysis of 68 antioxidant supplement trials found that taking beta-carotene and vitamin A and E supplements increased the risk of dying. [24] Although healthy participants were included in 21 of the trials, most of the studies included people who already had some type of serious illness. It was also difficult to compare interventions because the types of supplements, the dosages taken, and the length of time they were taken varied widely.
• The same authors conducted another systematic review of 78 randomized clinical trials on antioxidant supplements including beta-carotene, vitamin A, vitamin C, vitamin E, and selenium (alone or in combination). [25]   Again, the majority of trials included people with various established diseases. The study found that both people who were healthy and those with diseases taking beta-carotene and vitamin E supplements had a higher rate of death. The duration of the studies varied widely from one month to 12 years, with varying dosages.

If antioxidants were harmless, it wouldn’t much matter if you took them “just in case.” A few studies, though, have raised the possibility that taking antioxidant supplements, either single agents or combinations, could interfere with health.

• The first inkling came in a large trial of beta-carotene conducted among men in Finland who were heavy smokers, and therefore at high risk for developing lung cancer. The trial was stopped early when researchers saw a significant increase in lung cancer among those taking the supplement compared to those taking the placebo. [26]
• In another trial among heavy smokers and people exposed to asbestos, beta-carotene was combined with vitamin A. Again, an increase in lung cancer was seen in the supplement group. [27] Not all trials of beta-carotene show this harmful effect, however. In the Physicians’ Health Study, which included few active smokers, no increase in lung cancer or any other adverse affect was seen even after 18 years of follow-up. [10]
• In the SU.VI.MAX trial, rates of skin cancer were higher in women who were assigned to take vitamin C, vitamin E, beta-carotene, selenium, and zinc. [28]
• Vitamin E supplements were found to significantly increase the risk of prostate cancer by 17% in healthy men compared with those who took a placebo. These results came from the Selenium and Vitamin E Cancer Prevention Trial (SELECT) that followed 35,533 men for up to 12 years. [29]

High-dose antioxidant supplements can also interfere with medicines. Vitamin E supplements can have a blood-thinning effect and increase the risk of bleeding in people who are already taking blood-thinning medicines. Some studies have suggested that taking antioxidant supplements during cancer treatment might interfere with the effectiveness of the treatment. Inform your doctor if starting supplements of any kind. [1]

Antioxidants in food

One possible reason why many studies on antioxidant supplements do not show a health benefit is because antioxidants tend to work best in combination with other nutrients, plant chemicals, and even other antioxidants.

For example, a cup of fresh strawberries contains about 80 mg of vitamin C, a nutrient classified as having high antioxidant activity. But a supplement containing 500 mg of vitamin C (667% of the RDA) does not contain the plant chemicals (polyphenols) naturally found in strawberries like proanthocyanins and flavonoids, which also possess antioxidant activity and may team up with vitamin C to fight disease.  Polyphenols also have many other chemical properties besides their ability to serve as antioxidants.  There is a question if a nutrient with antioxidant activity can cause the opposite effect with pro-oxidant activity if too much is taken. This is why using an antioxidant supplement with a single isolated substance may not be an effective strategy for everyone.

Differences in the amount and type of antioxidants in foods versus those in supplements might also influence their effects. For example, there are eight chemical forms of vitamin E present in foods. However, vitamin E supplements typically only include one form, alpha-tocopherol. [1]

Epidemiological prospective studies show that higher intakes of antioxidant-rich fruits, vegetables, and legumes are associated with a lower risk of chronic oxidative stress-related diseases like cardiovascular diseases , cancer, and deaths from all causes. [30-33] A plant-based diet is believed to protect against chronic oxidative stress-related diseases.  [2] It is not clear if this protective effect is due to the antioxidants, other substances in the foods, or a combination of both. The following are nutrients with antioxidant activity and the foods in which they are found:

• Vitamin C : Broccoli, Brussels sprouts , cantaloupe, cauliflower, grapefruit, leafy greens (turnip, mustard, beet, collards), honeydew, kale , kiwi, lemon, orange, papaya, snow peas, strawberries, sweet potato , tomatoes, and bell peppers (all colors)
• Vitamin E : Almonds , avocado, Swiss chard, leafy greens (beet, mustard, turnip), peanuts, red peppers, spinach (boiled), and sunflower seeds
• Carotenoids including beta-carotene and lycopene: Apricots, asparagus, beets, broccoli, cantaloupe, carrots, bell peppers, kale , mangos, turnip and collard greens, oranges, peaches, pink grapefruit, pumpkin, winter squash , spinach, sweet potato , tangerines, tomatoes, and watermelon
• Selenium: Brazil nuts, fish, shellfish, beef, poultry, barley, brown rice
• Zinc : Beef, poultry, oysters, shrimp, sesame seeds, pumpkin seeds, chickpeas , lentils , cashews, fortified cereals
• Phenolic compounds: Quercetin ( apples , red wine, onions), catechins ( tea , cocoa , berries), resveratrol ( red and white wine , grapes, peanuts, berries), coumaric acid (spices, berries), anthocyanins (blueberries, strawberries)

Bottom line on antioxidants and disease prevention

Excessive free radicals contribute to chronic diseases including cancer, heart disease, cognitive decline, and vision loss. This doesn’t automatically mean that substances with antioxidant properties will fix the problem, especially if they are taken out of their natural context. The studies so far are inconclusive but generally don’t provide strong evidence that antioxidant supplements have a substantial impact on disease. Keep in mind that most of the trials conducted have had fundamental limitations due to their relatively short duration and inclusion of people with existing disease. At the same time, abundant evidence suggests that eating whole in fruits , vegetables , and whole grains —all rich in networks of naturally occurring antioxidants and their helper molecules—provides protection against many scourges of aging.

• National Center for Complementary and Integrative Health (NCCIH). Antioxidants: In Depth. https://nccih.nih.gov/health/antioxidants/introduction.htm Accessed 7/1/19.
• Carlsen MH, Halvorsen BL, Holte K, Bøhn SK, Dragland S, Sampson L, Willey C, Senoo H, Umezono Y, Sanada C, Barikmo I. The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutrition journal . 2010 Dec;9(1):3.
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25 Incredibly Iconic Love Triangles in Anime

L ove triangle anime series can be a lot of fun to watch, whether the triangle is the story's central focus or just one phase of the narrative. Plenty of anime series feel much more emotionally resonant and the characters are more sympathetic when true love becomes a battle that must be won. Love is never easy, especially when there's someone else competing for the same heart.

The best love triangle anime series tend to be romances where this kind of personal competition drives the entire plot. During a three-way romantic feud, the characters will be challenged to become better versions of themselves and figure out what true love really means to them. Sometimes, that is done for comedy's sake, and other times, some serious drama and heartbreak may follow the love triangle's resolution.

Updated by Louis Kemner on December 17, 2023: This list has been updated with five more examples of love triangle anime that keep everyone on their toes with intense romantic battles and drama.

Berserk: Guts x Casca x Griffith

Guts, a wandering mercenary, joins the Band of the Hawk after being defeated in a duel by Griffith, the group's leader and founder. Together, they dominate every battle, but something menacing lurks in the shadows.

Created by Kentaro Miura

First TV Show Berserk

Latest TV Show Berserk

Where to watch Crunchyroll

Video Game(s) Berserk: Millennium Falcon Hen Seima Senki no Sho, Sword of the Berserk: Guts Rage, Berserk and the Band of the Hawk

More About This Love Triangle:

• Griffith never returned Casca's feelings of adoration
• This love triangle mainly took place in the Golden Age
• Guts and Casca bonded over their mutual experiences with scars

The famed Berserk seinen manga/anime franchise may have a lot of brutal combat scenes and horror elements, but surprisingly, it also has a strong shojo/style emotional core. Berserk isn't violence for its own sake — its protagonists have strong personal reasons to fight and survive.

Casca is a heroic and noble swordswoman who loves Griffith for recruiting/saving her, but Griffith doesn't return those feelings. Instead, Guts and Casca become lovers, and Griffith feels left out. Interestingly, Griffith has strong feelings for Guts rather than Casca, and that makes them a complicated trio to watch in action throughout Berserk 's run. It's a love triangle anime unlike any other, with medieval war, blood and guts, horror, true love, and destiny all intertwined.

Oshi no Ko: Aqua Hoshino x Kana Arima x Akane Kurokawa

A doctor and his recently-deceased patient are reborn as twins to a famous Japanese musical idol and navigate the highs and lows of the Japanese entertainment industry as they grow up together through their lives.

Release Date 2023-04-12

Creator Aka Akasaka

Cast Yumi Uchiyama, Rie Takahashi

Main Genre Animation

Genres Drama, Fantasy

Rating TV-14

Seasons 1 Season

Production Company CyberAgent, Dogakobo, Kadokawa, Sentai Studios, Shueisha

Number of Episodes 12 Episodes

Oshi no Ko's New Love Triangle Is Exactly What The Show Needs for Season 2

• Akane isn't brave enough to stand up to Kana yet
• Mem-Cho strongly suspects this triangle's existence
• Aqua isn't in love with either girl yet in the anime
• The love triangle may overlap with the Tokyo Blade play

The idol anime series Oshi no Ko is many things at once: a dark drama, a partial isekai story, and certainly a love triangle anime. Protagonist Aqua Hoshino was once a full-grown doctor, but now he's a boy in his mid-teens who has become very special to not one but two girls his age.

The energetic tsundere Kana Arima may tease Aqua, but she can't help feeling attached to him, especially after he lifted her spirits with his Pieyon disguise. Meanwhile, Akane Kurokawa is deeply grateful that Aqua saved her life during her darkest moment, and she will do anything to win his heart, even mimic the late Ai Hoshino.

Bleach: Ichigo Kurosaki x Orihime Inoue x Rukia Kuchiki

Bleach  revolves around Kurosaki Ichigo, a regular always-grouchy high-schooler who for some strange reason is able to see the souls of the dead around him.

Release Date 2009-09-09

Creator Tite Kubo

Cast Hisayoshi Suganuma, Noriaki Sugiyama, Masakazu Morita, Hiroki Yasumoto, Fumiko Orikasa, Kentar It, Yuki Matsuoka, Shinichir Miki

Main Genre Anime

Genres Animation, Action, Adventure, Fantasy

• Bleach's fans ship Ichigo with Rukia because of their strong on-screen chemistry
• Fans detest Orihime because she's a threat to the IchiRuki pairing
• Other fans say the final IchiHime and RukiRenji pairings are the best

Even if Bleach is not a romance anime, it's still a love triangle anime in the eyes of shippers everywhere. Protagonist Ichigo Kurosaki had to choose between his charming classmate Orihime Inoue and the strong tsundere Rukia Kuchiki, and many Bleach fans contend that Ichigo chose wrongly.

In Bleach 's story, this love triangle causes a few bouts of heartache and drama until it is resolved, with Ichigo marrying Orihime and Rukia marrying her childhood friend Renji Abarai. There were good in-universe reasons for that arrangement, but fans still cite Ichigo/Rukia as the "true" pairing and the best part of this franchise.

Kaguya-Sama: Yu Ishigami x Miko Iino x Tsubame Koyasu

Kaguya-sama: love is war.

The proudly privileged top two students of an elite school each makes it their mission to be the first to extract a confession of love from the other.

Release Date 2019-01-12

Cast Yutaka Aoyama, Aoi Koga, Makoto Furukawa, Konomi Kohara

Genres Romance, Comedy, Anime

An intense anime love triangle eventually took root in the Kaguya-Sama: Love is War series. While the story's main focus is on Kaguya Shinomiya and Miyuki Shirogane, the anime made sure to give the dandere boy Yu Ishigami an interesting love life, too, even if he didn't intend to have one.

Yu Ishigami had eyes for the delightful and energetic Tsubame Koyasu, who inspired him with her radiant personality and willingness to help others. Meanwhile, Yu didn't realize that the tsundere Miko Iino was interested in him, and she had a tough time expressing those feelings of hers. At least she had her friend Kobachi to provide moral support.

My Hero Academia: Izuku Midoriya x Ochaco Uraraka x Himiko Toga

My hero academia.

A superhero-admiring boy without any powers enrolls in a prestigious hero academy and learns what it really means to be a hero.

Genre Adventure, Fantasy, Superhero

Language English, Japanese

Number of Seasons 4

Debut Date 2016-04-03

Studio Bones Inc.

My Hero Academia 375: What Does Ochacos Chat About Romance Mean?

• Izuku and Ochaco are both too shy to admit their mutual affection
• Ochaco was in denial that she and Himiko were similar
• Himiko loves Ochaco just as much she loves Izuku

My Hero Academia 's main anime love triangle concerns Izuku Midoriya/Deku and two memorable girls who only have one thing in common — their strong desire to be more like him. Ochaco Uraraka is a kind and selfless hero in training, while Himiko Toga is a twisted yandere criminal , but they do understand each other on a deep level.

Ochaco and Himiko have had a few emotionally charged fights where they blend their personal feelings with their opposing desires to win the heroes vs villains war. All that revealed a lot about what these girls think of themselves, Izuku, and each other while also suggesting that heroes and villains might not be so different after all.

School Rumble: Kenji Harima x Ouji Karasuma x Tenma Tsukamoto

School rumble.

A young high schooler is in love with an oblivious classmate; a delinquent classmate is in love with her. Both struggle to confess their feelings and their antics lead to crazy situations.

Release Date 2007-08-28

Creator Jin Kobayashi

Cast Caitlin Glass, Luci Christian, Brina Palencia

Genres Romance, Comedy

Rating TV-PG

Seasons 2 Seasons

Production Company Studio Comet

High school is a breeding ground for love triangles. Sometimes, it starts with a pair of people, like Kenji Harima and Tenma Tsukamoto, protagonists in the romantic comedy School Rumble. While they truly adore each other, they can't admit it.

Then, as they move to the next year of school, a new element is added: Ouji Karasuma. Where Kenji is a delinquent, Ouji is as straight-laced as they come. Still, he finds something amazingly wonderful about Tenma. However, he also has an issue letting his true intentions be known.

Honey and Clover: Shinobu Morita x Hagumi Hanamoto x Yuuta Takemoto

Honey and clover.

Yuuta Takemoto is a poor college student who lives in a dilapidated apartment building with his two friends, Shinobu Morita and Takumi Mayama. The series chronicles the students' story as they struggle through life and love.

Release Date 2005-04-14

Creator Chica Umino

Genres Drama, Comedy

Characters By Haruka Kud, Tomokazu Sugita, Hiroshi Kamiya

Production Company J.C. Staff

Sometimes, a love triangle becomes a love square. This is when a fourth person starts to have feelings for the pair attracted to the single person. Though symmetrical, it causes even more confusion.

Such is the case in Honey and Clover . A pair of art college students, Shinobu Morita and Yuuta Takemoto, fall for Yuuta Takemoto. There are two further complications besides the love triangle. First, Shinobu and Yuuta are roommates. Second, her friend, Ayumi, begins to fall for one of the young men.

Voltron: Legendary Defender: Keith x Lance x Princess Allura

Voltron: legendary defender.

Five teenagers become the last line of defense for the galaxy in an intergalactic battle against the evil alien force led by King Zarkon.

Release Date 2016-06-10

Creator Lauren Montgomery, Joaquim Dos Santos, Tim Hedrick

Cast Jeremy Shada, Kimberly Brooks, Bex Taylor-Klaus, Tyler Labine

Genres Animation, Sci-Fi, Action

Rating TV-Y7-FV

Production Company DreamWorks Animation Television, DreamWorks Animation, World Events Productions

In the early seasons of Netflix's Voltron: Legendary Defender , it seemed something was going on between Keith, Lance, and Princess Allura. However, it wasn't as obvious as other love triangles. While Lance was truly engaged in impressing Allura, the romance between her and Keith was more subdued.

The triangle was broken in season eight of the series. Allura finally succumbs to Lance's intentions and starts a romance with him. In the end, this is good news. The somewhat immature Lance becomes more caring and protective during this period.

Ef: A Tale of Memories: Kei Shindou x Hiro Hirono x Miyako Miyamura

Ef: a tale of memories.

A story of love, heartbreak and youth, as the stories of 6 different characters, which seem initially unrelated, begin to intertwine.

Release Date 2007-10-06

Creator Yu Kagami, Mikage

Rating TV-MA

Characters By Natsumi Yanase, Monica Rial, Hiroko Taguchi

Production Company Frontier Works, Geneon Universal Entertainment, Minori

A prime component of love triangles tends to be the interest of one childhood friend for another. Since the latter doesn't realize the former is infatuated with them, they turn to another person. This is the concept behind Ef: A Tale of Memories.

The childhood friends are Kei Shindou and Hiro Hirono. On Christmas Eve, Hiro lets Miyako Miyamura borrow his bike to stop a purse thief. When he discovers the bike destroyed and Miyako unconscious, the young man brings the girl to his home. This is where a romance starts to bloom, and Kei's jealousy emerges.

Golden Time: Kouko Kaga x Banri Tada x Nana Hayashida

Golden time.

Banri Tada is a freshman at a Tokyo law school. After an accident, he suffers severe memory loss. Despite the incident, he befriends fellow freshman, Mitsuo Yanagisawa, which leads him to the beautiful, yet obsessive, Kouko Kaga.

Release Date 2013-10-03

Creator Yuyuko Takemiya

Cast Mike Haimoto, Makoto Furukawa, Yui Horie

Amnesia is both a boon and a curse for Golden Time's protagonist, Banri Tada. The bad news is he forgot everything about his previous life. The good news is he can start anew. He does this by enrolling in law school, making this one of the few good college anime series out there.

One of his classmates, Kouko Kaga, begins to fall for him. However, as Banri's life starts to gel, in steps Nana Hayashida, a former childhood friend and romantic partner. Though he thinks repressed feelings are returning, Banri isn't sure if they are real or not.

White Album 2: Setsuna Ogiso x Haruki Kitahara x Kazusa Touma

White album 2.

White Album 2 orchestrates Haruki's final semester with complex romance and exhilarating music, as the curtains of the stage he so desired begin to open.

Release Date 2013-10-05

Genres Romance, Music

Characters By Takahiro Mizushima, Madoka Yonezawa, Hitomi Nabatame

Production Company Satelight

This love triangle begins as messy as it started. Setsuna Ogiso asks out Haruki Kitahara firstー before Kazusa Touma has the chance to tell him about her feelings. In addition to this, Haruki is interested in Kazusa but begins to date Setsuna because Kazusa never confesses her feelings.

While all of them get along as members of the Light Music Club, the real drama between the three is seen as the anime's plot unfolds, making it one of the most well-written love triangles in anime.

Neon Genesis Evangelion: Asuka Langley Sohryu x Shinji Ikari x Rei Ayanami

Neon genesis evangelion.

A teenage boy finds himself recruited as a member of an elite team of pilots by his father.

Release Date 1995-10-04

Creator Hideaki Anno, Masayuki, Kazuya Tsurumaki

Cast Megumi Ogata, Megumi Hayashibara, Kotono Mitsuishi

Genres Action, Adventure

Studio Gainax, Tatsunoko

Rei Vs. Asuka - Who Is Evangelion's Best Girl?

Neon Genesis Evangelion is less known for being a romance anime and more for being renowned as one of the most highly acclaimed psychological mecha anime in existence (if not the best) by fans. It's also a subversive mecha anime that questions the genre's foundations in intriguing ways.

On a more personal note, while most fans know about the tsundere Asuka and her conflicting feelings toward Shinji, some fans think of the dynamic between him and Rei as a show of affection. She does not know how to process or understand these feelings, however. Whatever side fans are on, they can indeed be considered a love triangle to many.

Re:Zero: Emilia x Subaru x Rem

Re:zero starting life in another world.

After being suddenly transported to another world, Subaru Natsuki and his new female partner are brutally murdered. However, Subaru awakens to a familiar scene, meeting the same girl again. The day begins to mysteriously repeat itself.

Release Date 2016-04-04

Main Genre Isekai

Studio White Fox

Main Cast Ysuke Kobayashi, Rie Takahashi, Sean Chiplock, and Kayli Mills

" I love Emilia " are words any fan of Re:Zero should know. Despite Subaru saying this to Rem for good reason, it doesn't hurt any less. The love triangle between Emilia, Subaru, and Rem can go on for a long time, as Subaru only has eyes for Emilia in a romantic sense.

Despite fans wishing for him to love Rem back for how dedicated she is, this love triangle might stay on a one-way streak for a long time — perhaps even until the light novel ends, as Rem and Emilia get along quite well. That love triangle definitely ranks among the most contentious and intriguing among all isekai anime series.

Yona of the Dawn: Hak Son x Yona x Su-Won

Yona of the dawn.

After being betrayed and run out of her home, the red-haired Princess Yona searches for four legendary dragons to take back her stolen kingdom.

Release Date 2014-10-07

Genres Action-Adventure

The love triangle in Yona of the Dawn is a tricky one, as Yona is in love with her childhood friend Su-Won. That is, until she tragically discovers that he killed her father and launched a coup d'etat against her kingdom.

On the other hand, Hak Son is her other childhood friend and bodyguard who has been in love with her as well. He simply watched her as she was in love with Su-Won. With the direction Yona of the Dawn has gone, it seems apparent who will win in this love triangle.

Kiss X Sis: Riko Suminoe x Keita Suminoe x Ako Suminoe

A young man in his last year of middle school trying to get into the same highschool as them is constantly being seduced by his slightly older step-sisters.

Release Date 2010-04-05

Creator Bow Ditama

Characters By Ken Takeuchi, Ayana Taketatsu, Yuiko Tatsumi

Production Company Feel, Gansis, Kdansha

Keita Suminoe has a love triangle between his twin stepsisters, Riko and Ako Suminoe. Ako is seen as the token child, helping her mother out with cooking and cleaning, but on the inside, she's a pervert.

Riko is more forward when speaking but has a shy personality. The twins can be told apart by their hairstyles. The series progresses far into Keita's relationship with his sisters. Kiss x Sis is known for its 12-episode OVA but received a 10-episode side series in 2010.

Nagi-Asu: A Lull in the Sea: Manaka Mukaido x Hikari Sakishima x Chisaki Hiradaira

Nagi-asu: a lull in the sea.

Long ago, humanity lived in the sea, but some humans longed to go to land and eventually left the sea behind. Now in present day, the two human types co-exist though their thinking has become as separate as they places they have lived.

Cast Bryce Papenbrook, Mikako Komatsu (Japanese), Natsuki Hanae

Production Company Geneon Universal Entertainment, Infinite, P.A. Works, Rondo Robe

Nagi-Asu: A Lull in the Sea gives viewers a love triangle of three childhood friends. The world has been separated between those who live on land and those who live underwater. Manaka Mukaido and Chisaki Hiradaira both have a love interest in Hikari Sakishima. Chisaki is more mature between herself and Manaka and doesn’t let her emotions dictate her thoughts often.

Hikari's calm demeanor is the opposite of Manaka. Emotionally driven, she struggles to realize what she really wants at times and ends up crying because of it. Despite this, Hikari still shows a preference for Manaka. She refuses to confess because she knows how Chisaki feels.

Skip Beat!: Ren Tsuruga x Kyouko Mogami x Shoutarou Fuwa

Kyoko went with her childhood friend, Sho to Tokyo to pursue his dream of becoming an idol.

Release Date 2008-10-05

Creator Yoshiki Nakamura

Cast Cristina Valenzuela, Bryce Papenbrook, Erica Lindbeck, Robbie Daymond

Production Company LME Love Me-bu

Kyouko Mogami was manipulated by Shoutarou Fuwa into being his servant to help him further his idol career. Vowing revenge, Kyouko enters the idol scene, starting a new life. Shou, who hides his full name in the series, is stuck up. While he views Kyouko as a stepping stone, he has genuine feelings for her.

Ren Tsuruga is the opposite of being super nice and uses Ren as a stage name. Separating Ren from his real name of Kuon Hizuri, Ren doesn’t think he is worthy of Kyouko, having met her in the past.

Kokoro Connect: Himeko Inaba x Taichi Yaegashi x Iori Nagase

Kokoro connect.

Five school friends experience strange supernatural phenomena that put their relationships to test.

Release Date 2012-07-07

Creator Sadanatsu Anda

Characters By Takahiro Mizushima, Aki Toyosaki, Miyuki Sawashiro

Production Company Enterbrain, King Records, Silver Link, Star Child Recording

Love triangles can be complicated, but they can become even more so when body-switching is possible. In Kokoro Connect , Himeko Inaba and Iori Nagase have a love triangle towards Taichi Yaegashi.

Himeko is the vice president of the Cultural Research Club, which gives her a professional aura, but she's sensitive on the inside. Iori is the president of the Cultural Research Club and is in love with Taichi as well but refuses to date him because of the body-switching epidemic. This allows the club members to switch bodies with one another for short periods. While in each other's bodies, they discover secrets that take a mental toll.

Chihayafuru: Taichi Mashima x Chihaya Ayase x Arata Wataya

Chihayafuru.

Chihaya meets a boy named Arata, a talented karuta player who thinks that she has a potential to become a great player. Chihaya then takes on a new dream of becoming Japan's best karuta player.

Release Date 2011-10-05

Creator Yuki Suetsugu

Cast Asami Seto, Mamoru Miyano

Seasons 3 Seasons

Production Company Madhouse, Video Audio Project (VAP)

In a classic example of a childhood friend against a transfer student, Chihayafuru has a love triangle between Taichi Mashima and Arata Wataya toward Chihaya Ayase. She's is a tomboy and a love interest for her childhood friend, Taichi.

Taichi has everything going for him but won't admit his feelings for Chihaya due to transfer student Arata. Though the opposite of Taichi, he shares a common interest in Karuta with Chihaya. Chihaya inspires him to keep playing.

InuYasha: Kikyou x Inuyasha x Kagome Higurashi

A teenage girl periodically travels back in time to feudal Japan to help a young half-demon recover the shards of a jewel of great power.

Release Date 2000-10-16

Creator Rumiko Takahashi

Studio Sunrise

Franchise Inuyasha

10 Ways InuYasha Feels Like A Shojo Anime

One of the most popular anime of the early modern era is InuYasha , which dates back to the fall of 2000. Inuyasha is a half-demon hybrid between a human and a demon dog. The love triangle in InuYasha is like no other. Kikyou is the shrine maiden in love with Inuyasha, who died but was brought back to life.

Kagome Higurashi is the reincarnation of Kikyou and has an interest in Inuyasha. Despite similar appearances, Inuyasha hasn't forgotten his feelings for Kikyo, which causes more than a little tension between the three of them. If fans count Naraku's dark lust for Kikyo, then the anime has a love square, but then again, Naraku stands no chance — emotionally, it's really between Kagome, Kikyo, and Inuyasha.