Greg Cochran has a hypothesis that male homosexuality is caused by some type of pathogen. There’s no direct evidence for this, but he points out that the other explanations, the “gay gene,” mutational pressure, advantages in females, ect, don’t make any sense, and his theory is the one that makes the most sense.
If it was spread by a pathogen wouldn’t you see high levels of variability in who “catches” it? Wouldn’t you expect to see towns in Sweden where 6% of the boys turn out to be homosexual(because the pathogen is unusually active there), and other towns where none of the turn out homosexual? I’m not saying I can be sure that pattern doesn’t exist, I just haven’t seen any evidence for it.
Cochran and Ron Unz had a heated argument about the subject back in 2013, but both agree that it is, in Cochran’s words, “hell on reproductive fitness.” It is certainly hell on reproductive fitness today but was it hell on reproductive fitness 500 years ago? Maybe not.
We know from prisons and boy schools that a non-trivial percentage of heterosexuals will participate in homosexual behavior in situations where they do not have access to females. Throughout much of evolutionary time homosexuality was criminalized and harshly stigmatized. Even in ancient Greece and Rome it was stigmatized to be the passive partner. Even if an individual was willing to take the risks of being homosexual he often would not have been able to find another homosexual partner. There were no bathhouses, to my knowledge, in 12th century Britain.
So it doesn’t seem that far fetched to assume that a non-trivial number of homosexuals would have behaved as heterosexuals. In addition they would have had incentives to do so, to have children who could take care of them in old age, to raise their social status, and to have a sense of legacy. In some areas having children itself would have been economically advantageous. Furthermore, it may be that homosexuals are significantly more likely to behave as heterosexuals when they cannot behave as homosexuals than are heterosexuals in the same circumstance.
Those advocating what I will call “political homosexuality” would be greatly repelled by that line of reasoning. It states that with dramatic social stigmatization of homosexuality it could, if not be “cured,” then be suppressed. For that reason it will be taboo just like HBD.
Unz wrote of homosexuality that it had a “a 3% impact on the reproductive fitness of a population.” This implies that 3% of the male population in one generation are homosexuals and wouldn’t reproduce. But if the real impact were an order of magnitude less whatever causes homosexuality would not be subject to the dramatic selection pressure Cochran and Unz assume would take place. It could be a result of the struggle between mother and child in utero. Or it could be whatever process causes homosexuality in some people gives an advantage, say in surviving pregnancy. Or it could be that whatever process causes homosexuality in male children gives some advantage to females. Or a pathogen. Or a combination of these things.