"One of the apparent physical changes in this “selection against aggression” is an inclination toward sex unattached to procreation, a wide-ranging sense of sexual being that often embraces homosexual and heterosexual urges, masturbation, and frottage. The bonobo handshake, it turns out, is a fundamental part of domestication. In dogs, Hare notes, one of the earliest clues for a tendency toward self-domestication is a degree of sexual indulgence: a “more subtle indication that dogs are less aggressive than wolves is that dogs tend to tolerate the inspection of their anogenital region by a stranger, while wolves can become aggressive even toward group members that attempt anogenital inspections.”
http://www.laphamsquarterly.org/essays/our-orgiastic-future.php?page=1
Joanna