WASHINGTON Neanderthals and modern humans interbred, probably when early modern humans first began to migrate out of Africa, according to a genetic study released on Thursday.
People of European, Asian and Australasian origin all have Neanderthal DNA, but not Africans, the researchers report in Fridays issue of the journal Science.
The study may help resolve the long-running debate over whether Neanderthals and modern humans did more than simply live side by side in Europe.
“Those of us who live outside Africa carry a little Neanderthal DNA in us,” said Svante Paabo of the Max Planck Institute in Munich, Germany, who led the study.
“The main finding is that there was gene flow from Neanderthals into all the ancestors of modern Non-Africans,” Dr. David Reich of Harvard Medical School in Boston, who worked on the study, told reporters in a telephone briefing.
“The proportion of Neanderthal-inherited genetic material is about 1 to 4 per cent. It is a small but very real proportion of ancestry in non-Africans today,” he said. The researchers used modern methods called whole genome sequencing to examine the DNA from Neanderthal bones found in Croatia, Russia, Germany and Spain.
It was not easy. “In those bones that are 30,000, 40,000 years old there is of course very little DNA preserved,” Paabo said. He said 97 per cent or more of the DNA extracted was from bacteria and fungi, and the Neanderthal DNA had to be pieced together. They compared the Neanderthal sequences to DNA sequences from five living Europeans, Asians and Africans.
UNDERSTANDING EVOLUTION
“You must appreciate that this international team has produced a draft sequence of a genome that existed 400 centuries ago,” Dr. Eric Green, director of the National Human Genome Research Institute at the National Institutes of Health, said in a statement.
“Their analysis shows the power of comparative genomics and brings new insights to our understanding of human evolution.” The results add to a picture of modern humans living alongside with and interacting on the most intimate levels with similar humans who have now gone extinct.
“There was interbreeding at some little level. I would prefer to leave it to others who want to quarrel over whether to call us separate species or not,” Paabo said. “We have shown that it was biologically possible for them to interbreed ... They were not genetically very distinct from us.”
In March Paabo and colleagues reported they had found a previously unknown human species in Siberia. They analyzed DNA from a finger bone to show the hominid, nicknamed “Woman X”, could have lived as recently as 30,000 years ago alongside modern humans and Neanderthals.
Scientists have for years speculated that several different species of humans lived side by side at various times over the past million years. But many would have lived in tropical zones where bones are not easily preserved. Paabo said modern-day Africans may carry some of that unknown DNA even if they do not have Neanderthal ancestors.
“Of course it is totally possible that also inside Africans, other archaic forms which we dont know (about) contributed to modern Africans today,” Paabo said. -Reuters
