Comparing the new sequences to the genome of another Neanderthal from the Caucasus region revealed that, in addition to splitting from a common ancestor around 150,000 years ago, Neanderthals experienced a major population turnover toward the end of their history, approximately 38,000 years ago. The researchers suggest that this could have been due to extreme cold periods, which led to the extinction of local populations and then recolonization from southern Europe or western Asia.
“We are now starting to have Neanderthal data from so many individuals that we can get a real picture of the genetic diversity within the species,” Morten Allentoft of the University of Copenhagen who was not involved in the study tells videnskab.dk (translated from Danish with Google Translate). “The study clearly shows that there was a geographical population structure (different characteristics of people in different geographic areas) in Neanderthals, just as we see it at Homo sapiens.”
According to the researchers, one surprising finding was the lack of modern human DNA in the Neanderthals’ genomes. Four of the Neanderthals lived at a time when modern humans were roaming Europe, but still they did not carry detectable amounts of modern human DNA. “It may be that gene flow was mostly unidirectional, from Neanderthals into modern humans,” study coauthor Svante Pääbo, the director at the Max Planck Institute for Evolutionary Anthropology, says in a statement.
The researchers note in the paper that the finding suggests “gene flow affected the ancestry of modern human populations more than it did Neanderthals.” However, they say, the sample of only five genomes is small and therefore human-to-Neanderthal gene flow cannot be excluded.