Before you get all grossed out and try to blame us for losing your lunch, take a moment to ponder the seriousness of this question. At some point in our evolutionary history, it made sense for us to lose body hair. The advantage in having little or no body hair has to do with the human ability of running upright. We are actually the most energy efficient runners (next to dogs) in the animal kingdom, and one way such a thing is possible is through an efficient cooling system, via sweat. Sweating works much more effectively without fur getting in the way of course.
Now, back to our original question.
Robin Weiss, a virologist at University College London, had an intimate revelation in the shower recently.
Public hair, he decided, developed as a sexual ornament. It became bushy and prominent after our ancestors split from non-human primates, he says, when we lost most of our other body hair. As it disappeared, human pubic hair acquired a new role as a prominent sexual ornament, a visual signal of sexual maturity and possibly a reservoir for sexual pheromones.
This theory is actually supported by examining the DNA of lice, both the human and gorilla versions.
Our ancestors and those of gorillas went their separate evolutionary ways at least 7 million years ago. But the lice that infect gorillas and modern humans didn’t become different species until much later – around 3.3 million years ago, as revealed through research in 2007 by David Reed of the University of Florida Natural History Museum in Gainesville.
Reed argues that gorilla lice crossed over to humans through incidental contact, such as humans sleeping in an abandoned gorilla nest. Weiss argues that the pubic hair in humans evolved to become coarser, which gave the gorilla lice something to get a grip on.
To back up his case Weiss visited zoos to peer at the groins of our closest relatives. He noticed that in other great apes, hair in the pubic region was if anything much finer and shorter than elsewhere on the body – the opposite of the human situation. It supported his argument that human pubic hair is different and probably unique, both in its evolution and in its physical appearance and purpose.