Cavemen, Chimps And Us

It is the holy grail of human paleontology, a window on a crucial moment in our evolution. Last week scientists at the Max Planck Institute in Germany announced they would attempt to sequence the Neanderthal genome--the complete DNA of the closest known relative to modern humans, a species that disappeared from the Earth about 30,000 years ago. It is the next best thing to having a living Neanderthal for comparison--and, in theory, if you know all the genes, you could create living Neanderthals. Not that anyone has any plans to do that.

What would they be like? From their skeletons, we know they would be robust and barrel-chested, with a heavy jaw and brow; from their caves it appears they could use primitive tools and buried their dead. But they seem to have lacked modern humans' capacity for abstract thought; although they spread overland through the Middle East and Europe, they apparently never crossed a body of water they couldn't see across. Anthropologists are divided on whether they had language, and although they presumably were able to breed with Homo sapiens, there's no clear evidence they ever did. Even bringing them back to life wouldn't necessarily clear up the mystery of how and why, having lived in Europe for some 200,000 years, they failed to survive contact with modern humans, who began spreading into Europe 50,000 years ago. The most widely held theory is that our ancestors killed them off.

In fact, we will probably learn as much about Homo sapiens from the effort as we will about Neanderthals, says Svante Paabo, the Swedish-born anthropologist who heads the project. Until now, the closest species with which humans could compare their DNA was the chimpanzee, whose genome is estimated to be 99 percent identical with ours. But that 1 percent still encompasses about 35 million indi-vidual chemical changes, accumulated over the 5 million to 7 million years during which the two species have been evolving apart. Humans and Neanderthals, though, shared a common ancestor in Africa only about 400,000 years ago, and Paabo estimates that their DNA will be as much as 99.96 percent identical. Somewhere in that 0.04 percent difference presumably lies the crucial molecular changes that led from stone axes to the cave paintings of Lascaux--and the cathedral at Chartres. The genes of interest include those involved in language, brain size and metabolism, says Edward M. Rubin, chief of genetics at Lawrence Berkeley Laboratory, which has its own ongoing study of Neanderthal DNA. Once you identify them you could put them in a mouse to see what they do--and understand exactly what it is that makes us human.

Apart from its benefits, the project is a technological tour de force, coming just three years after the first complete sequencing of the DNA of a living human being. That effort took 13 years and several billion dollars. Paabo's project should take two years, using new technology that has cut the cost to $500,000. (That's for a liv-ing human; using degraded and contaminated DNA from a 30,000-year-old fossil will be many times harder.) The machine is made by a Connecticut company called 454 Life Sciences, whose founder, biotech pioneer Jonathan Rothberg, said he'd hoped to use it to sequence DNA from a T. Rex, but getting usable genetic material from a fossil buried for 70 million years turned out to be impossible.

At least for now. Not that anyone is thinking of doing that.

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