Here’s a fascinating little bit of information I’ve just come across. At least it’s fascinating to me. I discovered it in the Evolutionary Psychology Textbook I’m reading for my class this year. The book is by David Buss, and is Evolutionary Psychology, 4th edition, 2012.
For evolutionary psychologists, homosexuality, particularly male homosexuality, has been difficult to explain. Although you will sometimes hear the argument that male homosexuals don’t reproduce and thus couldn’t pass on any genetic characteristics that lead to homosexuality, that is clearly not the case. Many homosexuals do reproduce and have reproduced down through time. However, there are differential reproduction rates. On average, male homosexuals produce about a fifth the offspring that male heterosexuals do. So why does this orientation continue to occur?
The traditional theory to explain this has been “Kin Altruism Theory.” Basically, it says that if male homosexuals channel more of their resources to their biological relatives than heterosexuals do, then the increased survival rate of those relatives will also carry along the genetic components involved in homosexuality. This is an example of something called “Indirect fitness” (how many copies of your genes get passed on by being carried by relatives) rather than “direct fitness” (How many children you have who directly carry your genes).”
The Kin Altruism Theory has garnered some support, but there are also plenty of studies that don’t support it. For example, in the US, male homosexuals often report greater estrangement from their relatives than heterosexual males do. I’ve talked about this theory, though, in most classes where I’ve discussed the potential basis for homosexuality.
Now we come to something I’ve only recently learned, which may be a much bigger influence on the issue. It’s called the “Female Fertility Hypothesis.” It turns out that the female relatives of male homosexuals, particularly their mothers and their aunts, have significantly higher reproduction rates than the same female relatives for male heterosexuals. In other words, the genetic aspects of male homosexuality could be carried down through the maternal rather than the paternal lines. I would also guess that this apparently greater fertility is hormone related, and hormone variations, especially in the fetal period, may explain many aspects of homosexuality.
Now ain’t that kind of cool?