Beyond the “Darwinian Puzzle”: Studying Same-Sex Sexual Behavior and Orientation as a Selective Force in Humans

Exclusive same-sex sexual orientation in humans is commonly regarded as an evolutionary “puzzle” or “paradox” because of its fitness-reducing nature. Elucidating the evolutionary origins of this trait has therefore been the main focus of evolutionary human scientists. However, as shown by evidence from other species, same-sex courtship and sexual behavior can also drive evolutionary change on other traits. In humans, this has mostly been overlooked. The present essay calls on evolutionary human scientists to study human homosexuality and bisexuality as selective forces in their own right, regardless of their evolutionary origins. It outlines different hypothetical selective pressures posed by the presence of same-sex orientations and behaviors in humans: selective pressures triggered by intersexual competition, or by challenges of identification and signaling of sexual orientation, selective pressures on kin selection for mechanisms driving differential parental investment, and selective pressure on the evolution (genetic or cultural) of antigay prejudice. By going beyond an exclusive focus on solving the “Darwinian puzzle” of the causes of homosexuality, evolutionary human sciences would contribute to a more holistic Darwinian understanding of human sexuality, in all its plasticity and variability.