The Psychology of the Pair-Bond: Past and Future Contributions of Close Relationships Research to Evolutionary Psychology

Romantic love evolved by co-opting mother-infant bonding

For 25 years, the predominant evolutionary theory of romantic love has been Fisher's theory of independent emotion systems. That theory suggests that sex drive, romantic attraction (romantic love), and attachment are associated with distinct neurobiological and endocrinological systems which evolved independently of each other. Psychological and neurobiological evidence, however, suggest that a competing theory requires attention. A theory of co-opting mother-infant bonding sometime in the recent evolutionary history of humans may partially account for the evolution of romantic love. I present a case for this theory and a new approach to the science of romantic love drawing on human psychological, neurobiological, and (neuro)endocrinological studies as well as animal studies. The hope is that this theoretical review, along with other publications, will generate debate in the literature about the merits of the theory of co-opting mother-infant bonding and a new evolutionary approach to the science of romantic love.

The Emerging Integration of Close Relationships Research and Evolutionary Psychology

Romantic relationships are a central focus of scientific inquiry within two psychological literatures—those on close relationships and evolutionary psychology—yet attempts to bridge these topics have been surprisingly rare. Recently, several lines of research have begun drawing from the methodological and theoretical traditions of each literature to inform the other. For example, evolutionary perspectives have recently made important contributions to the study of romantic relationships by highlighting the positive effects of negative emotions (e.g., jealousy) and the potentially negative implications of hormonal contraception use. In addition, the emphasis in the close relationships literature on relationship development over time has begun to refine scholars’ understanding of the ubiquitous evolutionary psychological distinction between short-term and long-term relationships as well as the classic concept of mate value. These lines of work exemplify how the edges of two intersecting literatures can generate intellectual sparks that ignite both fields.

Attachment to the Romantic Partner and Sibling: Attachment Hierarchies of Twins and Non-Twin Siblings

Previous studies have shown that romantic partners and siblings are important attachment figures. This study compares the attachment to the romantic partner with the attachment to the sibling as a function of the participant’s sibling type among monozygotic (MZ) twins, dizygotic (DZ) twins, and non-twin (NT) siblings. The results show that MZ twins prefer their sibling to their romantic partner whereas DZ twins are equally attached to their sibling and romantic partner. In contrast, NT siblings are more attached to their romantic partner compared to their sibling. These results indicate that genetic relatedness has profound impact on a person’s attachment hierarchy and the relative rank of the romantic partner and the sibling.

Leveling the Playing Field

Clear empirical demonstrations of the theoretical principles underlying assortative mating remain elusive. This article examines a moderator of assortative mating—how well couple members knew each other before dating—suggested by recent findings related to market-based (i.e., competition) theories. Specifically, competition is pervasive to the extent that people achieve consensus about who possesses desirable qualities (e.g., attractiveness) and who does not. Because consensus is stronger earlier in the acquaintance process, assortative mating based on attractiveness should be stronger among couples who formed a relationship after a short period rather than a long period of acquaintance. A study of 167 couples included measures of how long partners had known each other before dating and whether they had been friends before dating, as well as coders’ ratings of physical attractiveness. As predicted, couples revealed stronger evidence of assortative mating to the extent that they knew each other for a short time and were not friends before initiating a romantic relationship.