Modern humanity's ancient cousins, the Neanderthals, lived in small groups that were isolated from one another, suggests an investigation into their DNA. The analysis also finds that Neanderthals lacked some human genes that are linked to our behavior. (Related: "Why Am I Neanderthal?")

In recent years, experts in ancient DNA have mapped out the genes of Neanderthals, a species of human that vanished some 30,000 years ago. These gene maps have revealed that many modern people share a small part of their ancestry, and a small percentage of their genes, with those early humans.

Now moving beyond ancestry, researchers are comparing these ancient gene maps to those of modern humans. The comparisons may point to genes that make us uniquely human and uncover links to the origins of genetic ailments.

Compared to Neanderthals, humanity appears to have evolved more when it comes to genes related to behavior, suggests a team headed by Svante Pbo, a pioneer in ancient genetics at Germany's Max Planck Institute for Evolutionary Anthropology. Their study was published today in the Proceedings of the National Academy of Sciences.

They note in particular that genes linked to hyperactivity and aggressive behavior in modern humans appear to be absent in Neanderthals. Also missing is DNA associated with syndromes such as autism.

"The paper describes some very interesting evolutionary dynamics," said paleoanthropologist John Hawks of the University of Wisconsin at Madison.

The Neanderthal genes suggest that sometime after one million to 500,000 years ago, Neanderthal numbers decreased and the population stayed small, Pbo's group determined. A small population size would have been bad news for Neanderthals, Hawks said, because it would have meant that "natural selection had less power to weed out bad mutations."

Ancient Answers

Pbo and colleagues looked at the genes of two ancient Neanderthals, one from Spain and one from Croatia. They compared the DNA of those individuals to that of a third Neanderthal who had lived in Siberia and whose DNA had been analyzed in an earlier study, and to the DNA of several modern humans.

"We find that [Neanderthals] had even less [genetic] variation than present-day humans," Pbo said by email. Genetic diversity among Neanderthals was about one-fourth as much as is seen among modern Africans, he said, and one-third that of modern Europeans or Asians.

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Neanderthals Lived in Small, Isolated Populations, Gene Analysis Shows