Neanderthals may have died out 30,000 years ago, but their genetic legacy lives on. The sequencing of our closest relative's genome has revealed that anyone of non-African ancestry currently carries 1 to 4 per cent Neanderthal DNA.
After a small group of Homo sapiens left Africa thousands of years ago, they interbred with Neanderthals in the Middle East, new research suggests. These early modern humans moved on to Europe and Asia, and the genetic evidence suggests they were the ancestors of all modern humans from outside of Africa.
Although Neanderthals and early modern humans lived in the same parts of the world at the same time, until now the evidence has suggested there was no interbreeding, says Svante Pääbo of the Max Planck Institute for Evolutionary Biology in Germany.
"Those of us who live outside Africa carry a little Neanderthal DNA in us," he says. He and his colleagues estimate that 1 to 4 per cent of the genome of non-Africans is made up of Neanderthal DNA.
Neanderthals first appeared 400,000 years ago. The fossil record shows they were shorter and more powerfully built than modern humans, with barrel chests, large noses and forward-projecting faces.
They didn't find specific Neanderthal genes carried by present-day humans, like one for red hair. Instead, they say fragments of DNA are scattered through the genome.
Dr. Pääbo didn't expect to find evidence of interbreeding when he set out more than four years ago to construct the genome. The Neanderthal DNA was extracted from the leg bones of three women found in a Croatian cave in the 1970s and '80s. The bones were deliberately crushed and may have been cannibalized. New techniques allowed the researchers to extract DNA from half a gram of bone, and exclude the vast amount of genetic material from the microbes that have lived in the bones over the past 40,000 years.
When he and his team sequenced the Neanderthal genome and compared it with the genetic material of five people from Europe, Asia and Africa, they could see the "cave man" legacy in the non-African individuals.
Dr. Pääbo says that anyone who wishes to present the data from a racial perspective could argue that people from outside Africa are more primitive, or that it must somehow be good to have Neanderthal ancestry. "Neither is likely true," he says. "There is no basis to link it to any advantage of one group over another."
They also did a three-way comparison between the Neanderthal, present-day human and chimpanzee genomes. Some of our genes are slightly different from those carried by the Neanderthals, and scientists are zeroing in on them in hopes of understanding what makes us unique. One helps determine body shape, and may explain why our rib cages aren't bell-shaped. Several are involved in cognitive development, perhaps in social interaction and communication, and one plays a role in energy metabolism.
So far, 60 per cent of the Neanderthal genome has been sequenced, but work continues. The scientists say they are only beginning to catalogue and understand the features that make Homo sapiens different from our closest relatives. Edward Green, a researcher on the project from the University of California, says the Neanderthal genome offers a powerful tool to understand our evolutionary history. "We are looking to explore what changed, and why," he says.
The scientists reported their findings in the journal Science, published by the American Association for the Advancement of Science.