Analysis of the jawbone of a man who lived about 40,000 years ago reveals the closest direct descendant of a Neanderthal who mated with a modern human.
A modern human, who lived in what is now Romania between 37,000 and 42,000 years ago, Neanderthals was at least one of their ancestors. To be precise, it was his great-great-grandfather, as we go back in time of four generations.
For five years scientists know that human beings have in their blood, or better, in the DNA, traces of Neanderthal man. Yet so far it has been rather difficult to determine when (and where) our ancestors mated with their now extinct cousins. A new discovery, just published in the journal Nature, tells the story of the modern human with the most amount of Neanderthal DNA ever found so far. “I could hardly believe that we were lucky enough to hit upon an individual like this,” says study co-author Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig.
The find, named Oase 1, is nothing more than the jawbone of a male individual. From the time it was discovered, in 2002, his form has suggested to scientists that it belonged to a hybrid between Homo sapiens and Neanderthals. Yet those assumptions have remained controversial for years, until the analyzes have failed to dispel any doubt. “It’s really stunning,” says Oxford’s Tom Higham, an expert on the Neanderthal-human transition who was not involved in this research.
One of the things that leaves Higham amazed is the mastery of the techniques to tease genetic information, which allowed the scientists, the team was Qiaomei researcher at Harvard Medical School, to extract useful genetic information from so small DNA samples. “We tried in 2009 and we have failed,” says Pääbo, in whose lab has been working since then to improve the techniques of analysis, with results quite remarkable.
The genome sequenced from the sample was incomplete, but it was enough to allow the researchers to conclude that 6-9% of the genome of Oase 1 originates from Neanderthal. People living today have 4% at most.That difference is more significant than it might seem. “We found several – and huge – pieces of chromosomes that appear to be of pure origin of Neanderthal,” says Pääbo. That means pieces had to come from a relatively recent ancestor, since they hadn’t yet been broken up by the reshuffling that happens in each generation as parents’ chromosomes combine, he explains., The non-Neanderthal genome sequences, meanwhile, show that Oase 1 isn’t related to humans living today. His genealogical line died out at some point.
At the same time, the Neanderthal genome sequences extracted from the bone show that Oase 1 is not related to modern humans: its lineage, at some point, has stopped. These analyzes represent a tour de force in the field of biotechnology, and leading paleoanthropologists even closer to the answer of what Higham called the question a million dollars, what did extinguish the Neanderthal, and when? Last year the genomic analysis of a femur older than 45,000 years have suggested that modern humans and Neanderthals mated, between 50,000 and 60,000 years ago, in what is the modern Siberia. A number apparently very imprecise: it had jumped to conclusions too soon.
“The great breakthrough here,” Higham says, “is the ability to say ‘this specific person had a Neanderthal great-great-grandfather.’ That puts a human timescale on it.” If scientists can figure out when interbreeding took place in different parts of Europe and the Middle East, they’ll be able to say in detail just how rapidly humans spread across these regions, how long they were in contact with Neanderthals—and maybe tell us at last why our nearest relatives vanished.