He may have come down from the trees, but prehistoric man did not stop swinging. New research into Stone Age humans has argued that, far from having intercourse simply to reproduce, they had sex for fun.

Practices ranging from bondage to group sex, transvestism and the use of sex toys were widespread in primitive societies as a way of building up cultural ties.

http://jedijack-his-story.blogspot.com/2009/11/sex-games-of-stone-age-exposed.html