Hi there. A question came to my mind another day, and I decided to ask around so that I would know whether somebody studied this topic or not. I tried google, but thought it might be easier to try a forum. Here it goes.
Anal sex demands that the rectum is large enough to accommodate the penis. Because it is a so widespread practice, for example, see inmates in prisons, ordinary couples, etc., I suppose it has accompanied the human race since it beginnings. It seems, also, that that "ice man" found in Europe and that lived some 5,000 years ago had sperm in his rectum, which proves that he was either gay or raped.
Then, I think that in the early past of the human race, it may have happened that rectum might have been smaller, and natural selection operated so that only people with large enough rectum would pass its genes forward.
Is there any basis on what I am saying? Thank you for any contribution.