Fleshing out ancestral link to Neanderthals
DNA found in an ancient jawbone adds new detail to modern humans’ family tree.
Scientists have known that modern humans who live outside Africa have a small amount of Neanderthal DNA, but they haven’t been able to f lesh out when, where and how often our early ancestors mated with members of that now- extinct branch of the human family.
A new discovery, announced in the journal Nature, adds a piece to the puzzle. DNA testing of an ancient jawbone has confirmed that a man who lived in Romania about 40,000 years ago descended from a Neanderthal just four to six generations back — less than 200 years.
“To our amazement, this guy had three or four times more Neanderthal DNA than any modern human we had ever looked at,” said Svante Paabo, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and co-senior author of the study. “This is the first time we can say it’s dramatically more, and close in the family tree.”
The jawbone was discovered in a Romanian cave in 2002. Paabo’s analysis revealed that 6% to 9% of the man’s DNA came from Neanderthals.
The scientists were able to f igure out that one of those ancestors had been very recent by examining the size of the chunks of Neanderthal DNA in the man’s genome.
When the body produces an egg or a sperm, chromosomes split up and reorganize themselves in a process called recombination. The fewer the generations that have passed, the fewer such splits and reorganizations will have occurred, and the longer the stretches of DNA contributed from an ancestor will be.
The Neanderthal DNA in the jawbone was “distributed in big, big pieces on the chromosome,” Paabo said. “This indicates there has to be a Neanderthal relative very close in time.”
Scientists believe that the Neanderthal genes in people today were contributed early on, when modern humans ancestral to all non-Africans mated with Neanderthals in the Middle East.
The new discovery suggests that early Europeans also mated with Neanderthals later in human history, and probably on their own turf.
The DNA also revealed that the jawbone’s owner was part of an ancient population that is not related to later European groups ( including people living today).
The study was the latest of several in recent weeks that take advantage of improved analytical techniques to probe ancient DNA samples.
The studies include a pair of reports detailing the population history of Bronze Age Europe; another determining that the famous Kennewick man from Washington state is related to Native Americans living today; and a discussion of the evolution of dogs generated by studying DNA from a Siberian wolf that lived 35,000 years ago.