Kin-directed altruism and the evolution of male androphilia among Istmo Zapotec Muxes

Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis

“…Our data did not support the SAGH (at least its commonest, X-linked version) as a solution to the evolutionary conundrum of homosexuality but there are some alternative explanations worth considering. One such is the kin selection model, which posits that homosexual individuals increase inclusive fitness by helping their family members with raising their children (Wilson, 1975 , 1978 ), but studies which tested this hypothesis yielded mixed results (Bobrow & Bailey, 2001 ; Gómez Jiménez & Vasey, 2022 ; Vasey et al, 2007 ).…”

“…In such environmental conditions, any biological mechanism that increases the probability of homosexuality among later-born male siblings (e.g., increasing exposure to anti-Y antibodies from mothers, see Blanchard & Klassen, 1997 and Bogaert et al, 2018 ) is more likely to persist despite its reproductive costs. This is because having a later-born homosexual rather than heterosexual male in such contexts might: (1) reduce competition for inheritance among the brothers (see Apostolou, 2013 ) and potentially (2) increase the survival of the older brothers’ offspring via elevated kin-directed altruism among the younger homosexual brother (see Gómez Jiménez & Vasey, 2022 ). Altogether, this would increase the direct fitness of the older brothers and the inclusive fitness of the homosexual male.…”

Carving Non-Proximal Explanations for Same-Sex Sexual Orientation

“…This indirect reproduction may be increased behaviorally by kin selection, and it has been proposed that individuals displaying same-sex sexual preference could behave as "helpers," favoring reproduction by kin and thereby compensating for their direct reproductive cost (Trivers, 1974;Wilson, 1975). For homosexual men, this kin selection hypothesis is not supported in Western countries and Japan, although behavioral evidence (avuncular tendencies) has been obtained in Samoa, Mexico and Java (Gómez Jiménez & Vasey, 2022;Nila et al, 2018;Vasey & VanderLaan, 2009, 2010. However, a detailed study concluded that higher indirect reproduction did not fully compensate for homosexual men's direct reproductive cost, and the higher avuncular tendencies displayed by homosexual men marginally affected their number of nephews and nieces (Nila et al, 2018).…”