Have you not heard of contraceptives?
All that tlak of "giving birth to deformed children" flies out the window if, for example, the guy wears a condom.
LOL...Seems you missed the whole point. I simply was pointing out where the human aversion to breeding with close relatives came from and why we have mostly stopped. And back when the human race was young, there were no contraceptives. In fact, still today, good practicing Catholics are still forbidden to use them. By the time we get the homophobes, and the religious ones sorted, we will have pillaged the earth so badly, we will be extinct..
Nobody is holding a gun to your head to have heterosexual relationships, so why get your knickers in a knot about what others do. If a relationship is consensual and they are of age, it is none of your business.
By the way, all animal species, swing both ways. Of course they are more enlightened than the human species, they not only tolerate them but use them in a multitude of ways, depending on the species.