What Makes us Different?

Not very much, when you look at our DNA. But those few tiny changes made all the difference in the world

By Michael D. Lemonick and Andrea Dorfman Sunday, Oct. 01, 2006

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    The Neanderthals weren't nearly as primitive as many assume, observes Eddy Rubin, director of the Department of Energy's Joint Genome Institute in Walnut Creek, Calif. "They had fire, burial ceremonies, the rudiments of what we would call art. They were advanced--but nothing like what humans have done in the last 10,000 to 15,000 years." We eventually outcompeted them, and the key to how we did so may well lie in our genes. So two years ago, Svante Pääbo, the man who deconstructed the FOXP2 language gene and has done considerable research on ancient DNA, launched an effort to re-create the Neanderthal genome. Rubin, meanwhile, is tackling the same task using a different technique.

    The job isn't an easy one. Like any complex organic molecule, DNA degrades over time, and bones that lie in the ground for thousands of years become badly contaminated with the DNA of bacteria and fungi. Anyone who handles the fossils can also leave human DNA behind. After probing the remains of about 60 different Neanderthals out of the 400 or so known, Pääbo and his team found only two with viable material. Moreover, he estimates, only about 6% of the genetic material his team extracts from the bones turns out to be Neanderthal DNA.

    As a result, progress is maddeningly slow. And while he can't reveal details, Pääbo says he'll soon be announcing in a major scientific journal the sequencing of 1 million base pairs of the Neanderthal genome. And he says he has 4 million more in the bag. Rubin, meanwhile, is also poised to publish his results, but refuses to divulge specifics. "Pääbo's team has significantly more of a sequence than we do," he says. "Some of the dates will differ, but the conclusions are largely similar."

    Although Pääbo admits that he still hasn't learned much about what distinguishes us from our closest cousins, simply showing he can reconstruct significant DNA sequences from such long-dead creatures is an important proof of concept. Both he and Rubin agree that within a couple of years a reasonably complete Neanderthal genome should be available. "It will tell us about aspects of biology, like soft tissue, that we can't say anything about right now," Rubin notes. "It could tell us about disease susceptibility and immunity. And in places where the sequence overlaps that of humans, it will enable us to compare a prehistoric creature with chimps." Someday it may even be possible to insert equivalent segments of human and Neanderthal DNA into different laboratory mice in order to see what effects they produce.

    WHAT IT ALL MEANS

    Precisely how useful this information will be is hard to assess. Indeed, a few experts are dismissive of the whole project. "I'm not sure what Neanderthals will tell us," says Kent State's Lovejoy. "They're real late [in terms of human evolution]. And they represent, at best, a little environmental isolate in Europe. I can't imagine we're going to learn much about human evolution by studying them." Lovejoy is even more dismissive about claims that ancestors of chimps and humans interbred, arguing that using mutation rates in the genome to time evolutionary changes is extraordinarily imprecise.

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