What Head (and Other) Lice Tell Us About Evolution

The second episode of NOVA's big evolution special "Becoming Human" premieres tomorrow night at 8 PM ET/PT on PBS. Tuesday night's show focuses on Homo erectus, the ancestor who became "basically us" almost 2 million years ago, developing the first human societies. Much of what we know about Homo erectus comes from "Turkana Boy," the famous skeleton found by the Leakey team in Kenya in the early 1980's. An important part of what we know, though, comes from the genetic study of lice. And not just head lice. Using "paleoartists," digital filmmaking and the work done with Turkana Boy over the past two decades, the NOVA producers are able to paint a vivid portrait of  Homo erectus's role in key innovations - like using fire and developing social bonds - that make us human. The real action in the documentary starts about halfway through, when scientists tackle the question of how Homo erectus was able to obtain the protein necessary to support brain growth. Of course, stone tools played a huge role in making sure that the humans "went home for dinner and weren't the meal." Per NOVA, "most predators rely on strength or speed to kill their prey, and our ancestors had neither." Instead, according to Harvard's Dan Lieberman, Homo erectus relied on the combination of "endurance running and high activity in the middle of the day." Unlike animal predators, early humans were mostly hairless, giving them the ability to sweat and keep cool while running and tracking their prey over long distances. The evidence for Turkana Boy's hairlessness comes in part from the study of louse DNA. Hair is "rarely present in the fossil record" so researchers have turned to the study of parasites associated with hair, i.e. head and pubic lice. It turns out that the human head louse is very different from the human pubic louse. On top of that the pubic louse is closely related to lice found on gorillas. Viewers are left to draw their own opinions about how humans contracted pubic lice from gorillas. When humans lost their hair, the lice were forced to navigate "the hairless geographic barrier" between the head and pubic regions. By studying the genetic code of the two louse species, geneticists like Mark Stoneking of the Max Planck Institute can tell when the two species diverged from their common ancestor. Their research suggests that humans lost their thick coat of body hair almost three million years ago, paving the way for Turkana Boy to outrun and kill the meat he needed to feed his growing brain.