The Zoo We Bear

While we live with lots of microbes that make us healthier, it turns out; we also share our bodies with even more creatures: parasites and vermin. That may sound disgusting but they reveal many things about our past. For example, most of us harbor a mite that lives in the hair follicle of our faces. They're tubular and you've seen one if you've squeezed a greasy plug from a nose pore.

Scientists collected mites from the faces of seventy people of different origins and sequenced their mitochondrial DNA. As ancient humans left Africa, migrated, and became isolated populations, mites co-evolved along with them. So the type of mite you carry can help to identify your origins since they remain the same even generations later.

The tapeworms that infest mammals can also show when ancient humans began to eat meat. The assumption was humans acquired tapeworms when they domesticated animals some twelve thousand years ago. But modern humans share the same tapeworms as lions and hyenas. Perhaps humans acquired these parasites long before the domestication of animals, around five million years ago when they ate the same animals as the predators did.

As for when we lost our fur, we can look to the lowly louse. Some 7 million years ago, our human ancestors acquired head lice from Chimpanzees and four million years later, pubic lice from gorillas. This suggests the hair of the head and groin were no longer connected allowing for separate environments. So the multitude of organisms that live on us and in us are not only keeping us healthy, they tell us about our origins, our travels, and our story.