http://www.newscientist.com/article/dn26555-infanticide-drives-female-promiscuity-and-big-balls.html#.VGe-c8mkGZR

Evolutionary biologists argue that female promiscuity offers a natural protection against infanticide. By making it impossible for males to know who is the father of a particular child, the risk of infanticide is lowered. The study notes that such behavior is most common among mammalian species wherein infanticide occurs most frequently and even goes so far as to state that,

The study also finds that the ancestor to all great apes - including humans - probably committed infanticide.

Despite the obvious link, the authors (predictably) fail to acknowledge the giant elephant sitting in the middle of the room.