The Competitor Conversion Hypothesis of Homosexuality

We explore a theoretical model for the evolution and persistence of a gene (G) promoting exclusive same-sex behaviour among males in a sexually reproducing species. The model presumes three preconditions: (1) evolved incest avoidance mechanisms; (2) conditional gene expression based on cues indicating the presence of close male relatives; and (3) susceptibility of rival males to conversion through contact with homosexual individuals. The rare gene conditionally expresses homosexuality in males, causing them to forgo direct reproduction and specialize in converting unrelated rivals. This competitive disruption amplifies the resulting reproductive surplus for kin (brothers) via non-linear price effects within a structured mating market. Specifically, the conversion reduces the equilibrium mating 'prices' females can charge, indirectly yielding a super-additive fitness benefit to related heterosexual males. Given its male-limited benefits and female-mediated costs, such a gene would be strongly favoured if located on the Y chromosome, with potential for counter-evolutionary pressures on the X chromosome. The model offers novel insights into the interplay between genetic architecture and reproductive economics, and suggests testable predictions for the genetic origins of homosexuality and population-level mating outcomes under natural conditions.