Recently, they did a large study to determine the cause of sexual behaviour and find a "gay-gene": https://geneticsexbehavior.info/ https://geneticsexbehavior.info/wp-content/uploads/2019/08/ganna190830.pdf. They concluded that there is no such thing. My guess is that indeed, nutrition plays a main role, but there are for sure other factors like Tyler mentioned. You can´t blame everything on nutrition. Even in nature there are examples of gay animals. Did they eat soy? I doubt it. Still, I think that nutrition is a very important factor that one should not miss. I know at least 2 people that were fed soy milk when they were babies, and they turned out to be gay.
The whole idea of finding an "X gene" that every person with X has, and every person without the gene doesn't have X, is quite dumb. Very few genes work like this. Rather, genes work synergistically and combine with each other to create all sorts of different possibilities.
Diseases are caused either by defective genes, or by toxicity accumulation, poor nutrition/lifestyle, or by artificial experience that teaches someone to go against their very nature; or by a combination or sequence of any or all of the above: For example, toxicity buildup can damage genes. Mental disorders can cause someone to poison themselves with drugs and chemicals. Damaged genes can also predispose someone to a mental disorder; etc.
If one were to be able to understand all there is to know about how genes combine to form particular individuals, I suspect we'd be able to tell which people with which genes have much higher or much lower chances of becoming gay.
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RE: Tyler, the testosterone idea is incomplete, as this only applies to men who become gay because they feel more like women than men, but it does not encompass all gay men, such as those that become gay because they feel more manly by dominating boys instead of girls. All of that said, on average, and because a large proportion of gay men are of the first type, gay men have much lower testosterone than non-gay men.
How about this idea?
Genetic statistics show we are descended from a ratio of 1 male having children with 5 females.
Therefore plenty of males are not chosen for the job.
Maybe being a reproductive male is a sort of pinnacle of biology?
There is the theory that in H-G tribes/bands, weak or low status men only pretend to be gay so they will be trusted by the alphas to protect the females when they're not around; and in doing so have their only chance at reproduction.