Scientists Discover New Proof of the Neanderthal Within Us

(May 6) -- It turns out there really is a little caveman in a lot of us.

An international team of scientists has for the first time decoded the complete Neanderthal genome, and the results, to be reported in the May 7 issue of Science, offer new insights into our closest evolutionary relatives and an exciting new way to explore the genetic basis of what makes humans unique. But the big news? The scientists also found evidence that humans and Neanderthals interbred. And the results of that prehistoric coupling can be found in most people's DNA.

By comparing the Neanderthal genome with those of five present-day humans from different regions across the world, the scientists found that roughly 1 to 4 percent of the genomes of non-African people derive from our extinct relatives. "It's a small but very real proportion," says Harvard geneticist David Reich, one of the paper's co-authors.

Neanderthals turned up around 400,000 years ago, then disappeared -- from the fossil record at least -- roughly 300 centuries ago. Humans were around back then as well, and archaeological evidence suggests the two species lived in some of the same areas of Europe and modern Asia during the last 50 or so millennia of the Neanderthals' run. In fact, AOL News reported on one such hot spot, Siberia's Altai Mountains, back in March.

Given the evidence, there has been a long-standing debate over whether the two species interbred, according to Reich. "We're able to largely resolve that controversy," he says.

But why did the Neanderthal DNA show up only in the non-African subjects? For one thing, Neanderthals were concentrated in parts of Europe, Asia, Siberia and the Middle East but not Africa. Based on the genetic evidence, the scientists suspect that the intermingling of the two species probably occurred between 45,000 and 80,000 years ago, when modern humans were moving out of Africa for the first time. Neanderthals populated the Middle East at this time, and the two groups may have encountered each other there. Then these humans would have spread across the continents and carried the genetic signals of that encounter with them.

Along with suggesting a saucier version of our pre-modern history, the new paper could enable scientists to pinpoint some of the genes that make humans special. The researchers have already highlighted genes associated with cranial development, energy metabolism and physiology as targets of future study.

The findings also represent a serious technological achievement. The scientists extracted this genomic information from tiny samples taken from three fossilized bones collected from the Vindija Cave in Croatia. The bones were roughly 40,000 years old and largely contaminated by DNA from microbes.

"I really thought, until six or seven years ago, that it would remain impossible, in my lifetime, to sequence the entire nuclear genome of Neanderthals," says lead author Svante Paabo, a geneticist at the Max Planck Institute for Evolutionary Anthropology. "That changed with technological developments."