Children all over America are returning to school this fall and I’m sure parents have done all they can to prep their youngsters—which hopefully involves any and all vaccines and boosters. But not even the most diligent efforts toward preventative health care can save your child from the bug that has been plaguing playgrounds for decades. I’m talking about cooties. You can try self-immunization---using your index finger to trace two circles punctuated by two dots on the back of your hand accompanied by prescription-strength poetry---but constant re-application is almost always necessary. And the folded paper cootie catchers do nothing but induce a placebo effect in affected persons.
But in all seriousness, it may surprise some of you to know that cooties are in fact quite real---but they’re not some strange, highly infectious disease afflicting persons of the opposite gender. “Cootie” is simply a slang term for lice, three types of which call the human anatomy home: head lice, which live exclusively on the scalp; body lice, which live on clothing and migrate onto the skin to feed; and pubic lice, which should be pretty self-explanatory. Offhand, the fact that we can harbor multiple varieties of the same parasite seems pretty lousy. However, research is showing that because these critters are so intimately adapted to our bodies, lice are quite useful in illuminating milestones in human evolution.
In a 2004 study, University of Florida mammalogist David Reed and his colleagues nitpicked over head and body louse DNA from all over the world. They found two genetically distinct types of head louse, one found worldwide and another exclusive to the Americas. Strangely enough, this would be possible if the two groups of louse had been living on the heads of two different species on different continents, the scientists say. Reed argued that both modern and archaic humans had their own types of lice. As modern humans---Homo sapiens---began to move out of Africa, they would have intermingled with Homo erectus---Homo sapiens’ evolutionary predecessors that were living in Asia and East Africa---picking up their archaic parasites along the way to the New World. These findings help to bolster the “Out of Africa” theories of human origins and early migrations. (Author Guy Gugliotta wrote a piece on human migrations for the July 2008 issue of Smithsonian.)
Another louse study done in 2008 by Reed and Didier Raoult on 1,000-year-old Peruvian mummies did a terrific job at debunking one of the long-standing myths of the Age of Exploration: the idea that Europeans introduced lice to the Americas. While Europeans were guilty of bringing new diseases, like smallpox, the mummies show that lice were alive and well in the New World well before gold- and glory-hunting explorers graced these shores. Furthermore, the DNA of the mummies’ lice is identical to that of lice originating in Africa, providing additional support for the diffusion wave model of human evolution and migration.
Lice also indicate when humans began wearing clothes. Early humans were covered with ape-like hair but started showing skin some 3.3 million years ago when they took to living in hot, savannah environments. (Bare skin promotes sweating and is a terrific way to keep cool, ergo much of the hair had to go, evolutionarily speaking.)
As humans started moving out of the savannah and into cooler climes, they had to start covering up. When they started wearing clothes, however, was always something of a gray area. But this past spring, a team of researchers led by Andrew Kitchen of Pennsylvania State University took a look at louse DNA and traced when head lice diverged from body lice, which have claws tailored to cling to fabric. That divergence was approximately 190,000 years ago. (A 2003 study led by geneticist Mark Stoneking gave a date of approximately 107,000 years ago.) The team deduced that humans began making and wearing clothing around this time.
And of course some of you out there may wonder where that intimate, third variety of louse came from. Oddly enough, the DNA record shows that its closest relative is the louse native to gorillas. Science has yet to provide an explanation as to how this happened. Bad case of “beer goggles” perhaps?
With that in mind, it’s almost certain that school-aged persons will soon be marching down to the nurse’s office to be tested for lice. And while we may have fun with them by way of games and songs, cooties are not to be taken lightly.
Jesse Rhodes is an editorial assistant for Smithsonian and blogs at Around the Mall.