How do anthropologists know where to dig for fossils?

How do anthropologists know where to dig for fossils?

How do anthropologists know where to dig for fossils?

Answers to your questions about the news.
March 25 2010 4:19 PM

Comb the Desert!

How do anthropologists know where to dig for fossils?

Sibera. Click image to expand.
Siberia

Anthropologists unearthed a single pinky finger in Siberia that may have belonged to a previously unknown human species, according to a report released Wednesday. Preliminary DNA evidence suggests that the early human, who died in a cave between 30,000 and 48,000 years ago, was neither a Neanderthal nor a modern man. How do anthropologists decide where to look for ancient humans?

In most cases, they wait for an amateur to get lucky, then make their move. Anthropologists can't see what's under the first layer of earth without digging—ground-penetrating radar isn't sensitive enough to distinguish fossils from the surrounding rock—and there's too much land and too few anthropologists to dig up every site where the geology favors bone preservation. So most anthropologists wait until a farmer, geologist, or curious child stumbles upon an interesting bone. Then they use geological maps, Google Earth, and good, old-fashioned walking around to determine the likelihood that there's more to discover in the vicinity.

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Caves are particularly promising areas for excavation. Early humans used them to hide from predators and the elements. Neanderthals, and possibly other early humans, may even have buried their dead in caves as early as 200,000 years ago. (Skeptics argue that early man simply liked to rest in hollows with a little snack and sometimes died in his comfy spot.) Some researchers, therefore, survey caves— particularly those in Siberia, where scientists are looking for evidence of the early humans of Eurasia and North America—without waiting for a fortuitous amateur find. They look for painted walls and artifacts like tools or bones lying on the ground. If they find nothing, they may dig a test hole about 1 meter square and a few inches deep. If that doesn't turn anything up, they usually abandon the site.

Finding our earlier ancestors in the deserts of Africa, where caves are virtually nonexistent, is much more challenging. If a passer-by discovers a fossil, researchers look around for sedimentary rock—a particularly good material for fossil preservation. Because it's difficult to secure funding for a new excavation, almost all of our digging in Africa has been limited to places where people have previously happened upon bones, a fairly small portion of the continent between the East African Rift and the Indian Ocean.

Bonus Explainer: The Siberian early human lived during the Pleistocene ice age, so researchers assume that he or she would have worn clothes for insulation. When did humans start dressing up? At least 100,000 years ago. Human raiment is not typically preserved in the fossil record, so researchers have turned to lice genetics for hints. Body lice diverged genetically from other louse species about 100,000 years ago. Because body lice live primarily in our clothing, scientists use that moment of differentiation as the likely era when humans started dressing themselves.

It's possible, however, that humans started wearing clothes even earlier. We know that pubic lice jumped over to humans from gorillas—our genetically distinct head lice migrated from chimpanzees—about 2 million years ago. And since pubic and head lice probably couldn't have coexisted on the same body if there was a hairy highway connecting their favorite anatomical spaces (one would have beaten out the other for all the available resources), it's likely that we had lost our body hair by then. Some claim that humans donned clothing shortly after that, but others argue that there's no reason our ancestors would have needed clothing in steamy Africa.

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Explainer thanks Andrew Hill of Yale University and Pat Shipman of the Pennsylvania State University.

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Brian Palmer covers science and medicine for Slate.