Proximate and Ultimate Perspectives on Romantic Love

Abstract

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.

Behavioral genetics

“…The neuropeptides oxytocin and vasopressin and the neurotransmitter dopamine facilitate pair-bonding, while polymorphisms in oxytocin, vasopressin, and dopamine genes, and their receptor-rich brain regions, are involved in basic motivational processes, sexual satisfaction, and pair-bonding across species (Acevedo, Poulin, Collins, & Brown, 2020;Diekhof, Richter, Brodmann, & Gruber, 2021). These kinds of findings provide evidence that pair-bonding and romantic love maintenance in humans are parts of a broad mammalian strategy for reproduction and long-term attachment which is influenced by basic reward circuitry and genetic factors that create individual differences in sexual behaviors, sexual preferences, and pair-bonding (Acevedo et al, 2020;Bode & Kushnick, 2021;Luoto et al, 2019a). For more detailed discussions of these topics, readers may wish to refer to Acevedo et al (2020) who used a mixed methods approach-both neuroimaging and gene samplingto study how genetic polymorphisms and brain activation are related to romantic love in newlywed couples (see also Bode & Kushnick, 2021, for a broader review).…”

“…These kinds of findings provide evidence that pair-bonding and romantic love maintenance in humans are parts of a broad mammalian strategy for reproduction and long-term attachment which is influenced by basic reward circuitry and genetic factors that create individual differences in sexual behaviors, sexual preferences, and pair-bonding (Acevedo et al, 2020;Bode & Kushnick, 2021;Luoto et al, 2019a). For more detailed discussions of these topics, readers may wish to refer to Acevedo et al (2020) who used a mixed methods approach-both neuroimaging and gene samplingto study how genetic polymorphisms and brain activation are related to romantic love in newlywed couples (see also Bode & Kushnick, 2021, for a broader review). Another study by Diekhof and colleagues (2021) genotyped participants for genetic polymorphisms in the dopamine system and created a multilocus genetic composite (MGC) score which reflected the additive effect of different alleles conferring relative increased dopamine transmissionwhich in turn influences reward processes and behaviors across species (see also Kringelbach & Berridge, 2010;Luoto et al, 2019b;Struik, Sanna, & Fattore, 2018).…”

Why are depression symptoms scores greater in people experiencing romantic love?

“…Given that there is some evidence that depression symptoms scores are associated with romantic love (including among adolescents), it raises the question of why this is the case. Similar or related biological mechanisms may be one explanation (see Bode & Kushnick, 2021). Both depression and romantic love are associated with changes in functional connectivity in networks involving the amygdala, medial prefrontal cortex, and nucleus accumbens (Dean & Keshavan, 2017;Song et al, 2015).…”

“…It is common at the beginning of a romantic relationship but can occur in the absence of a romantic relationship. The mechanisms that cause romantic love, its development across the lifespan, its functions, and its evolutionary history have been described in detail elsewhere (Bode & Kushnick, 2021). That review suggested that romantic love has neurobiological and endocrinological similarities with depression.…”

“…In romantic love, the behavioral activation system is probably engaged, manifesting in elevated mood (Brand, Luethi, von Planta, Hatzinger, & Holsboer-Trachsler, 2007;Bajoghli et al, 2011;Bajoghli et al, 2013;Bajoghli et al, 2014;Brand et al, 2015). The goals are to facilitate courtship, sex, and pair-bonding with a loved one (see Bode & Kushnick, 2021). The association between romantic love and depression symptoms scores suggests that the BIS may also be engaged, promoting symptoms of depression.…”