Although evidence in modern humans does not support the prosociality hypothesis of homosexuality, the sociosexuality hypothesis has received notable support

Luoto, S. Did Prosociality Drive the Evolution of Homosexuality? Arch Sex Behav (2020). https://doi.org/10.1007/s10508-020-01749-0

Introduction
Possible evolutionary origins of homosexuality is a topic that has received broad interest in the scientific community. In a recent article, Barron and Hare (2020) argued that same-sex sexual attraction (SSSA) was selected for in recent human evolution because of its “non-conceptive social benefits” in hominids and other primates in which there was strong selection for heightened prosociality and sociosexuality. Barron and Hare pitched this as a new hypothesis but failed to discuss existing work which has proposed and tested similar ideas in various ways. In formulating the prosociality hypothesis, Barron and Hare dismissed other hypotheses that have received broad empirical support, namely gender shift and endocrinological hypotheses of homosexuality. The purpose of this article is to critically discuss Barron and Hare’s prosociality hypothesis in order to help other researchers and the general public to better assess the plausibility and novelty of the prosociality and sociosexuality hypotheses of same-sex sexual attraction and behavior.

Conclusion
Although evidence in modern humans does not support the prosociality hypothesis of homosexuality, the sociosexuality hypothesis has received notable support, especially regarding a gender shift to heightened sociosexuality in nonheterosexual women (Luoto et al., 2019a, b). The biological and evolutionary underpinnings of homosexuality suggest that there are other proximate mechanisms than genetic ones (e.g., endocrinological and neurodevelopmental ones), and other ultimate functions than prosociality, that cause and maintain homosexuality in human and nonhuman animal populations. Current evidence provides little support for the hypothesis that prosociality is one such ultimate evolutionary function.

Check also Prosociality and a Sociosexual Hypothesis for the Evolution of Same-Sex Attraction in Humans. Andrew B. Barron and Brian Hare. Front. Psychol., 16 January 2020. https://www.bipartisanalliance.com/2020/01/same-sex-sexual-attraction-evolved-as.html