Masculinised brain and romantic jealousy: Examining the association between digit ratio (2D:4D) and between- and within-sex differences

Relationship status and gender-related differences in response to infidelity

Introduction

The sexual imagination hypothesis suggests that responses to a partner's infidelity emerge from the sociocultural factors that affect individuals' imagining of that occurrence irrespective of biological sex, including relationship status (i.e., the experience of a serious, committed relationship). Nevertheless, evolutionary psychological perspectives predict that responses to a partner's infidelity emerge from a sex-specific evolved innate mechanism.

Methods

A lower 2D:4D digit ratio is associated with more robust responses to a partner's sexual infidelity. In this study, participants (660 males and 912 females) were requested to measure finger lengths, reactions to their partners' sexual and emotional infidelity, and relationship status.

Results

A logistic regression and multiple regression analyses revealed that relationship status was uniquely associated with responses to a partner's sexual and emotional infidelity beyond the effects of sex and 2D:4D. Those in committed relationships were more upset or distressed over their partners' infidelity, particularly over sexual infidelity, than those not in committed relationships.

Discussion

The results supported the sexual imagination hypothesis indirectly, while evolutionary psychological perspectives were met with skepticism. Our findings implied that sex differences in jealousy result from relationship status, and that responses to partners' infidelity are more alike than different.

Confronting Intrasexual Rivals

The current research sheds light on a physiological mechanism potentially underlying confrontational responses to infidelity. Findings suggest that responses to infidelity threats in adulthood are shaped by hormonally mediated masculinization of the brain in utero. 2D:4D digit ratio (widely regarded as an index of prenatal testosterone exposure) moderated behavioral and endocrinological responses to infidelity threat. After an infidelity prime (but not a control prime), lower (more masculine) 2D:4D was associated with a greater tendency to approach attractive same-sex targets (intrasexual rivals) and with heightened increases in circulating testosterone, a hormone related to a variety of aggressive and confrontational behaviors.