Just a year ago, when Svante Pääbo, a paleogeneticist at the Max Planck Institute in Germany, announced he was going to reconstruct the Neanderthal genome, the project seemed unlikely to succeed. Despite sifting aggressively through Neanderthal fossils, scientists had managed to unearth only bits of mitochondrial DNA, secondary genetic blueprints that describe the energy-producing units of cells but not the entire organism. Suddenly, things are looking up: Pääbo recently declared he has found nuclear DNA (the global kind) in a 45,000-year-old Croatian Neanderthal museum specimen and has sequenced a million base pairs of it.
Pääbo now estimates that he will have a complete draft of the Neanderthal genome within two years, and the doubters are turning quiet. His studies of this nuclear DNA are already yielding a better understanding of our big-boned cousins. For example, based on his reconstructed genetic sequence, Pääbo calculates that modern humans last shared a common ancestor with Neanderthals about 500,000 years ago—a good 300,000 years before Homo sapiens had even evolved. That and other genetic differences suggest we didn't interbreed extensively, says Pääbo, but it doesn't mean Neanderthals couldn't have contributed a few genes here or there.
More DNA could settle the question and fill in many details about what made Neanderthals tick. "In some ways it will serve as a DNA time machine to understand their biology," says Eddy Rubin, a Lawrence Berkeley National Laboratory geneticist collaborating with Pääbo. Using what we know about human genes, for example, could help us extrapolate details like Neanderthal hair and eye color, their genetic diseases, and possibly even their language capabilities.
It also brings up the inevitable question: Could we clone a caveman? With no complete, fully intact DNA specimen, that scenario is still way beyond our current technology, Rubin says: "It's at the outer realm of science fiction."