How do Humans Maintain Homosexuality in the Population at High Numbers?

 Dr. Tatiana spends some time in chapter 9 explaining homosexuality in the animal kingdom. She notes that it is common amongst multiple species and can be caused by a handful of factors. She mentions that it could be due to desperation, for pleasure, genetically based, for power, or as a reproductive suppression behavior. Our question: "how are high numbers of homosexuality maintained in high numbers" is touched on in the book. If there is a genetic basis, genes can still be passed on if individuals who practice homosexuality are not exclusively homosexual. This means that they are still able to reproduce and pass their propensity to be homosexual onto their offspring. Dr. Tatiana also suggests that genes for homosexuality could be maintained if natural selection favors them. When this book was written less was known about the genetic basis of homosexuality. 

'Evolutionary Origins of Homosexuality' discusses numerous pieces of evidence that supports an argument that homosexuality is a part of evolution and confers certain benefits. This article is focused primarily on male homosexuality. This paper mentions multiple studies to back up its statements, but its writers did not do any independent research. 

This paper notes that homosexuality is determined in utero when genes for sexuality develop in response to the mother and her surrounding environment. Twin studies provide evidence for this statement. Often when one identical twin is homosexual, the likelihood that the other is also homosexual is increased. But there is no one gene that determines sexuality. Heritability of homosexuality is also supported by maternal fecundity data. One theory states that gay males come from families with fertile women, which suggests that the genes that can determine homosexuality can also confer reproductive success (Figure 1). The high reproductive success of a gay man's family also might compensate for his lowered reproductive success.

Figure 1. This graph shows the fecundity of maternal aunts and grandmothers and the number of children within the family and how there is a significant amount of homosexuals that come from families with more children. 

The paper moves onto the discussion of epigenetic factors. Epigenetic factors activate or inactivate genes based on the environment. There is a correlation between homosexuality and male birth order. The more sons a woman has had, the more likely one of her younger sons is going to be gay. This could be because her womb is producing more estrogen with each subsequent birth, and the environment is activating epigenetics that are connected to homosexuality. Another theory suggests that higher stress while a mother is pregnant can lead to homosexuality in males. 

It is also believed that homosexual men experience neuropsychological differences as compared to heterosexual males. Homosexual males scored higher on standardized tests of verbal skills. The paper mentions a study of three longitudinal databases from the US and the UK where intelligence and homosexuality may be linked. More intelligent children tended to identify as homosexual as adults. It also claims that studies have determined that there are structural differences in the brains of homosexual males and heterosexual males. 

The paper also determines the Kin Selection Theory of Homosexuality. This is where the evolutionary advantage did not necessarily develop in direct reproductive success, but instead in helping to raise kin. The higher emotional IQ's that tend to correlate with homosexual men can help make his family more functional and resistant.  

There is still not one clear cut answer as to why homosexuality continues to persist in our population despite its lack of success as a reproductive strategy. While it is difficult to answer this question, there are multiple theories and studies that have sought out answers. This can give us a better understanding of a sexuality that has been stigmatized and misunderstood for so long. 

O'Keefe, J., O'Keefe, E., & Hodes, J. (2018). Evolutionary Origins of Homosexuality. Retrieved 2021, from https://www.researchgate.net/profile/James-Okeefe-6/publication/323880861_Evolutionary_Origins_of_Homosexuality/links/5ab12a6f0f7e9b4897c37acd/Evolutionary-Origins-of-Homosexuality.pdf