Where Pubic Lice Comes From

March 10, 2010

One of the more embarrassing STD's a person can contract is pubic lice. You may have been itching for awhile, and finally, you had to figure out what was causing the annoying symptoms. You check out yourself as best you can with a small mirror and shout, "Yikes! I've got crabs!"

Humans can be infested with one of two types of lice: pthirus pubis and pediculus humanus. The former is the official name for pubic lice, while the latter infects the human head and body. A recent article in BioMed Central's Journal of Biology, which is open to the public, offers an explanation for why the two species are separate entities.

Eureka Moment: Gorilla Lice

University College London's Robert Weiss says he was caught by an idea while considering why lice would have separated into two different groups, since according to evolutionary theory; human ancestors were hairy from top to toe. "I was having difficulty envisioning a clear separation of habitats between the groin and other parts of our ancient common ancestor. My 'eureka moment' came, appropriately enough, in the shower: although naked apes have pubic hair, surely our hairy cousins don't?"

Pthirus pubis, known by laymen as, "crabs," are believed to have evolved from the gorilla louse, pthirus gorillae, which is quite similar in structure.  But things get interesting when one takes into account that a genetic analysis performed by David Reed from the University of Florida shows the separation occurred some 3.3 million years ago, though humans are thought to have evolved from gorillas quite some time before this, at least 7 million years ago. Does this mean that early humans contracted pubic lice from their almost-relatives, the gorilla?

Gorilla Hosts: Pubic Lice

Weiss says we needn't assume that the two species were engaging in sexual relations, a la King Kong and notes that predators are capable of catching parasites from their prey. As humans butchered gorillas, there was likely to have been some close contact that allowed Pthirus to jump from the gorilla to the human hosts. A modern example of how this works can be seen in the way that HIV infects humans who slaughter chimpanzees for bush-meat.

In short, while you have every right to think of head lice as a unique family heirloom, handed down from earlier human ancestors, pubic lice should be considered as a more modern acquisition bestowed upon reluctant human beings by the more hirsute members of our evolutionary relations.

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