Cavemen among us: Some humans are 4 percent Neanderthal

Whatever the final answer, the question of interbreeding had long puzzled paleoanthropologists, says David Reich, a population geneticist at the Harvard Medical School in Boston and a member of the team reporting the discovery in Friday's issue of the journal Science.

Neanderthals and anatomically modern humans occupied the same general real estate in Europe and western Asia for roughly 50,000 years until the Neanderthals went extinct some 30,000 yeas ago. Scientists have reasoned that there must have been some level of interbreeding during that time.

With these new results, "there's very strong evidence that it did occur. There was gene flow from Neanderthals to the ancestors of all modern non-Africans," Dr. Reich says. The genome comparisons the team performed indicate a small amount of interbreeding that likely occurred during the period when they first came into contact with each other some 50,000 to 80,000 years ago.

Humans, Neanderthals, chimps: three of a kind

The team also compared the genomes of modern humans and Neanderthals to those of chimpanzees – genetically the closet living relative to humans.

Based on the fossil record, the split between chimps' ancestors and those of ancestors of humans and Neanderthals is thought to have occurred some 5 million to 6 million years ago. The split between modern humans and Neanderthals is estimated to have taken place in Africa some 400,000 years ago.

The researchers found that 99.7 percent of the Neanderthal genome is identical to modern humans. Both Neanderthal and modern human genomes are 99.8 percent identical to that of chimpanzees.

The results and their further refinement are expected to yield a treasure-trove of information on what makes modern humans distinct from Neanderthals, humans' closest extinct relative. The team says it already has spotted differences between the two in genes researchers have associated with brain development, skull structure, metabolism, skin types, and wound healing.

Related:

• X Woman: Not human, not Neanderthal, what is she?
• Fossil DNA tells tales of red-haired Neanderthals
• What happened to the Neanderthals? Check their DNA.

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