Man’s closest ancestors, the Neanderthals, disappeared about 30,000 years ago, leaving little more than their bones behind. But those bones may help decipher what makes us human, and they are beginning to divulge their ancient secrets. Now researchers have revealed a first draft of the complete Neanderthal genome, a sequence of three billion or so base pairs.

At a joint press conference held during the annual meeting of the American Association for the Advancement of Science, Svante Pääbo, head of the project and director of genetics at the Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany, said that this first overview covers about 63 percent of the Neanderthal genome. Most of it derived from just a half gram of bone removed from 38,000-year-old fossils excavated from Vindija Cave in Croatia. “The attraction of the Neanderthal genome,” Pääbo says, “is that it’s our closest relative in all categories, and we diverged only about 300,000 years ago.”

“Studying them will tell us what makes modern humans really modern, and really human; why we are alone; why we have these amazing capabilities,” says Jean-Jacques Hublin, who is the director of human evolution at Max Planck and was involved in the research.

Despite its draft quality, the genome is already beginning to reveal a few of our ancestors’ traits. As researchers expected, Neanderthals lacked the lactase gene, present mostly in European humans, which allows adults to digest milk. But the researchers confirmed that the ancient hominid did share with us the only gene known to be implicated in speech and language, FoxP2, which earlier studies had only suggested was the case. “There’s no reason to assume they couldn’t articulate as we do,” Pääbo says.

However, the new data do little to further the idea that humans and Neanderthals interbred–something that has been the subject of much debate, but for which most experts agree there is little evidence. “We have looked at the contribution from Neanderthals into the present-day [human] gene pool–that is very little, if anything,” Pääbo says. “But the cool thing is that interbreeding is a two-way street, and for the first time we can look at it the other way, from human ancestors into Neanderthals. So we’re currently analyzing if we see evidence in the Neanderthal genome of a contribution from human ancestors.”

A little over two years ago, Pääbo and his colleagues, including a team headed by Michael Egholm at 454 Life Sciences, published the first proof that they could extract genetic material from Neanderthal bones. This is an incredibly complex, obstacle-riddled task when dealing with such ancient DNA. The longer bones lie in the ground, the more their DNA degrades, leaving researchers with only short fragments with which to work. Microbes also invade a skeleton and saturate it with their own DNA; in even the most well-preserved bones, only 4 percent of the DNA belongs to its original owner. Because the genome in question is from man’s closest relative, things get even more complicated. Human contamination is inevitable, and researchers must find a way to differentiate between human and Neanderthal DNA, even while the two species share almost all the same genes.