Anal sex was de rigeur 5,000 years ago whilst cave drawings suggest practice millions of years old.
The Bonobos
http://pin.primate.wisc.edu/factsheets/entry/bonobo have been observed having anal sex with each other, suggesting possibility that the primates that CAME before us did so with plenty of anal in their tastes and diet.
Clearly we are bio-evolutionary beings: could it be that our sphincters have adapted perfectly for the multiple purposes over the millenia and the mankind is evolving into better ass fuckers?
Bio Evolution Rocks.
19Trees