Most mammals have the same ratio of heterosexual to homosexual offspring in their population (some animals were found to be more gay than average).
It seems a natural byproduct of heterosexual sex.
Either homosexuality has some evolutionary benefit to the group (less sexual competition, more childless people to take care of a relative's kids etc), or as most scientists believe, heterosexual sex simply statistically must lead to some people having certain chemical and chromosomal combinations that lead to homosexuality and types of transgenderism.
For example, we know that the more sons a mother has, dramatically increases the likelihood of the last son being born gay, due to depleted testosterone in the mother in the months prior to birth.
We also know (www.scientificamerican.com/article/homop...-hidden-homosexuals/) from studies that homophobes tend to be more likely to have repressed homosexual lusts. That's why you often see Republican politicians or religious pastors bashing homosexuals in public, and then being caught out having gay sex several years later. Or why hyper-conservative or hyper-masculine groups (the navy, the Taliban etc) which bash gays, are more likely to have gay sex than average.
Most macho heroes also tend to seem gayer and more camp as time goes on. Think about all those macho action heroes you're watching on TV, with their skin tight spandex, topless muscles, always pounding and penetrating each other with fists and bullets and long hard phallic weapons.
It's all gay as hell.
This is probably because all humans start off in the womb as female. After birth, masculinity then has to define itself in opposition to what it wrongly believes femininity is: soft, weak, insecure etc. But the need to constantly affirm this masculinity is itself an unconscious admittance of insecurity, and so traditional masculinity is itself super effeminate and gay on its own terms
This is why the straightest thing you can do as a guy is to play with another dude's beautiful erection.