Our Grandmothers' Legacy: Challenges Faced by Female Ancestors Leave Traces in Modern Women's Same-Sex Relationships.

Investigations of women's same-sex relationships present a paradoxical pattern, with women generally disliking competition, yet also exhibiting signs of intrasexual rivalry. The current article leverages the historical challenges faced by female ancestors to understand modern women's same-sex relationships. Across history, women were largely denied independent access to resources, often depending on male partners' provisioning to support themselves and their children. Same-sex peers thus became women's primary romantic rivals in competing to attract and retain relationships with the limited partners able and willing to invest. Modern women show signs of this competition, disliking and aggressing against those who threaten their romantic prospects, targeting especially physically attractive and sexually uninhibited peers. However, women also rely on one another for aid, information, and support. As most social groups were patrilocal across history, upon marriage, women left their families to reside with their husbands. Female ancestors likely used reciprocal altruism or mutualism to facilitate cooperative relationships with nearby unrelated women. To sustain these mutually beneficial cooperative exchange relationships, women may avoid competitive and status-striving peers, instead preferring kind, humble, and loyal allies. Ancestral women who managed to simultaneously compete for romantic partners while forming cooperative female friendships would have been especially successful. Women may therefore have developed strategies to achieve both competitive and cooperative goals, such as guising their intrasexual competition as prosociality or vulnerability. These historical challenges make sense of the seemingly paradoxical pattern of female aversion to competition, relational aggression, and valuation of loyal friends, offering insight into possible opportunities for intervention.