This new perspective comes from a study of ancient DNA carried out by an international research team. Rolf Quam, a Binghamton University anthropologist, was a co-author of the study led by Anders Götherström at Uppsala University and Love Dalén at the Swedish Museum of Natural History, and published in the journal Molecular Biology and Evolution.
Focusing on mitochondrial DNA sequences from 13 Neandertal individuals, including a new sequence from the site of Valdegoba cave in northern Spain, the research team found some surprising results. When they first started looking at the DNA, a clear pattern emerged. Neandertal individuals from Western Europe that were older than 50,000 years and individuals from sites in Western Asia and the Middle East showed a high degree of genetic variation, on par with what might be expected from a species that had been abundant in an area for a long period of time. In fact, the amount of genetic variation was similar to what characterizes modern humans as a species. In contrast, Neandertal individuals that come from Western Europe and are younger than 50,000 years show an extremely reduced amount of genetic variation, less even than the present-day population of remote Iceland.
These results suggest that western European Neandertals went through a demographic crisis, a population bottleneck that severely reduced their numbers, leaving Western Europe largely empty of humans for a period of time. The demographic crisis seems to coincide with a period of extreme cold in Western Europe. Subsequently, this region was repopulated by a small group of individuals from a surrounding area. The geographic origin of this source population is currently not clear, but it may be possible to pinpoint it further with more Neandertal sequences in the future.
“The fact that Neandertals in western Europe were nearly extinct, but then recovered long before they came into contact with modern humans came as a complete surprise to us,” said Dalén, associate professor at the Swedish Museum of Natural History in Stockholm. “This indicates that the Neandertals may have been more sensitive to the dramatic climate changes that took place in the last Ice Age than was previously thought.”
Quam concurs and suggests that this discovery calls for a major rethink of the idea of cold adaptation in Neandertals.
“At the very least, this tells us that without the aid of material culture or technology, there is a limit to our biological adaptation,” said Quam. “It may very well have been the case that the European Neandertal populations were already demographically stressed when modern humans showed up on the scene.”
– source sciencedaily.com