The Louse That Roared

Newsweek‘s cover story has two fun facts I didn’t know about human evolution.

The first is kind of a head-scratcher:

Head lice live in the hair on the head. But body lice, a larger variety, are misnamed: they live in clothing. Head lice, as a species, go back millions of years, while body lice are a more recent arrival. [Mark] Stoneking, an evolutionary anthropologist, had a hunch that he could calculate when body lice evolved from head lice by comparing the two varieties’ DNA, which accumulates changes at a regular rate. (It’s like calculating how long it took a typist to produce a document if you know he makes six typos per minute.)

That fork in the louse’s family tree, he and colleagues at Germany’s Max Planck Institute for Evolutionary Anthropology concluded, occurred no more than 114,000 years ago. Since new kinds of creatures tend to appear when a new habitat does, that’s when human ancestors must have lost their body hair for good — and made up for it with clothing that, besides keeping them warm, provided a home for the newly evolved louse.

I say it’s confusing because this story says that humans picked up pubic lice from gorillas 3 million years ago:

Rather than close encounters of the intimate kind, researchers explained humans most likely got the lice, which most commonly live in pubic hair, from sleeping in gorilla nests or eating the apes.

“It certainly wouldn’t have to be what many people are going to immediately assume it might have been, and that is sexual intercourse occurring between humans and gorillas,” explained researcher David Reed of the Florida Museum of Natural History. “Instead of something sordid, it could easily have stemmed from an activity that was considerably more tame.”

For both these stories to be true, then pubic lice (aka “crabs”) must be different from body lice, and indeed this paragraph from the second story says just that:

Humans are unique among primates in that we host two different kinds of lice — one on our heads and bodies (Pediculus), the bane of many schoolchildren, and pubic lice (Pthirus). In comparison, chimpanzees have only head lice and gorillas only pubic lice.

So, based on my very limited (although rapidly increasing) knowledge of louseology, the body lice discussed in the Newsweek article evolved from head lice 114,000 years ago, thanks to that newfangled innovation called “clothing” (aka “threads”), which was necessitated by the loss of our precious follicular material (aka “fur”).

Still, both stories suggest that all this sound and fury from the world of parasitic research indicates a data point for the loss of human body hair:

The evidence suggests gorilla lice began infesting humans about 3.3 million years ago. In contrast, humans and gorillas diverged in evolutionary time about 7 million years ago. The fact the lice took up residence where they did may have coincided with human loss of most hair on the rest of their bodies and the lack of any other suitable niche to live, Reed said.

So, while it’s great that both theories of parasitic invasion are precise — 114,000 years ago for body lice, 3.3 million years ago for pubic lice — we’re left with a gap of 3.2 million years for the loss of human body hair.

This paper (pdf) doesn’t answer the question of when we lost our hair, but does offer some reasons why, including the idea that without hair we humans became less susceptible to parasites.

So, if you’re keeping score at home, lice give us important clues to our evolutionary history, even though we apparently evolved into hairless apes to rid ourselves of lice.

How’s that for a paradox?

“Oh, look at Og over there with his big brain and flat face. Does he think he can just evolve into something special? Loser!”

Here’s the other bit o’ science from the Newsweek article that caught me by surprise:

New research also shows that “progress” and “human evolution” are only occasional partners. More than once in human prehistory, evolution created a modern trait such as a face without jutting, apelike brows and jaws, only to let it go extinct, before trying again a few million years later. Our species’ travels through time proceeded in fits and starts, with long periods when “nothing much happened,” punctuated by bursts of dizzying change, says paleontologist Ian Tattersall, co-curator of the American Museum’s new hall. …

In 2001, a team digging in Chad unearthed what it claimed was the oldest fossil of an ancestor of humans but not chimps. If so, it must have lived after the two lineages split. Trouble was, Sahelanthropus tchadensis (nicknamed Toumai, the local word for “child”) lived close to 7 million years ago. The genetic data, pointing to a human-chimp split at least 1 million years later, suggest that Toumai is not the ur-hominid — the first creature ancestral only to human and not our chimp cousins — after all.

If Toumai is not our ancestor, what is he doing with such a humanlike face and teeth, which look like those of species 5 million years his junior? “A 7 million-year-old hominid should be just starting to look like a hominid, not have a trait you see so much later in the fossil record,” says paleoanthropologist Bernard Wood of George Washington University.

Amazing that they never even consider the possibility that space aliens made multiple attempts to create the human species on Earth. And they call themselves scientists!

BTW, if you really are trying to keep score, check out this timeline of human evolution.

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