The answer is yes, there is at least some cave man biology in most of us. Between 1 percent and 4 percent of genes in people from Europe and Asia trace back to Neanderthals.
"They live on, a little bit," says Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Researchers led by Paabo, Richard E. Green of the University of California, Santa Cruz, and David Reich of Harvard Medical School compared the genetic material collected from the bones of three Neanderthals with that from five modern humans.
Their findings, reported in Friday's edition of the journal Science, show a relationship between Neanderthals and modern people outside Africa, Paabo said.
That suggests that interbreeding occurred in the Middle East, where both modern humans and Neanderthals lived thousands of years ago, he said.
"People are interested in the question: 'By what route did I get here?' And the idea that there is a faint echo of Neanderthals" is interesting, reflected Richard Potts, director of the Human Origins Program at the Smithsonian's National Museum of Natural History.
"I'm really impressed by the nuance they've been able to pick up," said Potts, who was not part of the research group. "The papers are a really good antidote to the all-or-nothing findings of previous studies."
Humans trace their origins out of Africa into the Middle East and then on to other parts of the world. The genetic relationship with Neanderthals was found in people from Europe, China and Papua-New Guinea, but not people from Africa.
Todd Disotell, an anthropologist at New York University, suggested that more Africans should be sampled.
"My guess is, as we sample more Africans we're going to find some of these old lineages in Africa," said Disotell, who was not part of the research team. He noted that the researchers looked at the genomes of a west African and a south African, but not someone from northeast Africa, where he said the mixture would be more likely to have occurred.
And Paabo agreed that his finding does not mean that only people from outside Africa have some cave man biology. With more study it might be found in some Africans also.
Indeed, Laura Zahn, associate editor of life sciences at the journal Science, said she anticipates the report will provide material for geneticists and anthropologists to quarrel over for years.
Reich noted that while there was a flow of genes from Neanderthals to modern humans, there is no indication of gene movement the other way, from humans to Neanderthals.
The closest extinct relative to modern people, Neanderthals existed from about 400,000 years ago to about 30,000 years ago. They coexisted with modern humans for 30,000 to 50,000 years in Europe and western Asia.
While many people think of Neanderthals as very primitive, they had tools for things like hunting and sewing, controlled fire, lived in shelters and buried their dead.
Asked if the findings show differences between Africans and non-Africans, Paabo replied that people who want to present data in some sort of racist perspective would find a way to do so. He said, one way to look at this data could be to say people outside Africa are more primitive, while another way could be to say there is something beneficial about being part Neanderthal.
"There is no basis to link this to some sort of advantage of one group over another," he said.
Erik Trinkaus, an anthropologist at Washington University in St. Louis, who has long argued that Neanderthals contributed to the human genome, welcomed the study, commenting that now researchers "can get on to other things than who was having sex with who in the Pleistocene."
