Mystery of the crabs possibly solved

Pubic lice (Pthirus pubis)

Have you ever wondered why there are two distinct species of lice that infest human beings: nits and the crabs that rummage through the undergrowth? Others have, and the mystery may have now been solved thanks to University College London biologist Robin Weiss, who came up with a possible explanation while attending to his ablutions.

The mystery concerns the separation of lice into two groups when the ancestors of humans were uniformly hairy.

“My ‘eureka moment’ came, appropriately enough, in the shower,” says Weiss. “Although naked apes have pubic hair, surely our hairy cousins don’t?”

Research a few years ago by University of Florida parasitologist David Reed and others indicates that the split occurred around 3.3 million years ago. Yet the separation between gorillas and the chimpanzee-human line took place around four million years before that.

This would suggest that humans caught the crabs from their more hirsute fellow anthropoids, but one shouldn’t assume the worst when it comes to this inter-species contact. According to Weiss, pubic lice could have hopped across to their new hosts during hunting. After all, it was hunting which allowed the retrovirus that evolved into HIV to spread from chimpanzees to humans.