Why women cheat: testing evolutionary hypotheses for female infidelity in a multinational sample

While scholars largely agree men's infidelity evolved by increasing offspring quantity, the evolutionary drivers of women's infidelity remain debated. The "good genes" (dual mating strategy) hypothesis posits infidelity allows women to pair the preferred genes of an affair partner with the preferred investment of their primary partner (Gangstad & Thornhill, 1998). The mate-switching hypothesis instead argues infidelity helps women obtain a new mate without a period of deprivation (Buss et al., 2017). To test these hypotheses, we conducted a preregistered survey of 254 individuals from 19 countries and 6 continents who were previously or currently engaged in infidelity. We measured individuals' perception of their primary partner and their affair partner across four domains: physical attractiveness, personal attractiveness, attractiveness as a co-parent, and overall desirability (mate value). We also asked participants to report their motivations for the affair. Consistent with a dual mating strategy, women experienced stronger physical attraction to their affair partners and stronger parental attraction to their primary partners. Contrary to the mate-switching hypothesis, women did not prefer their affair partners overall, parentally, or personally. There were no significant gender differences in these findings, suggesting strategic dualism in men as well. Our qualitative data revealed a more nuanced story at the individual level, with participants reporting motives consistent with a variety of evolutionarily coherent strategies. While our quantitative results speak to the relevance of the dual-mating hypothesis to understanding infidelity, our findings also suggest that seeking infidelity's primary explanation in either gender is, perhaps, too simple an approach to the issue.