Lice Evolution Tracks the Invention of Clothes

Cooties come in three varieties: head lice, body lice and pubic lice. While head lice live and feed only on the scalp, body lice feed on the body’s skin but live in clothes. Humans have always had hair, but clothes are a more recent development. Figuring out just when body lice evolved, therefore, can give us hints as to when we became the trendy, clothes-wearing species we are today.

Smithsonian writes:

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.

In 2003, a German researcher decided to put this theory to the test. He measured the difference between snippets of DNA in the two louse subspecies. Because DNA picks up small, random mutations at a more or less constant rate, the greater the difference between the DNA of divergent but related species, the longer the separation. As it turned out, the body louse branched off from the head louse about 70,000 years ago, give or take 42,000 years.

Clothing must have evolved at that time, too, the researchers figured. We also began drawing and carving, weaving, creating tools and burying our dead. In other words, we underwent a cultural revolution.

Orion elaborates on the implications:

They are wearing clothes—lice-filled clothes, to be sure, but clothes nonetheless. Momentously, they are using language. And they are dramatically increasing their range. Homo sapiens is exploding across the planet.

The date is not set in stone, however. A 2010 study that performed a second DNA analysis claimed that the divergence between head and body lice actually occurred about 190,000 years ago. Though there is some discrepancy, we can estimate that humans began wearing clothes roughly 200,000 to 50,000 years ago.

Smithsonian clears up the remaining evolutionary mystery: the pubic louse.

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?

More from Smithsonian.com:

Cootie Catchers Say Lice Reveal Lots About Human History
The Deep History of Dinosaur Lice

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.