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DNA analysis shakes up Neandertal theories

Western Europe has long been held to be the “cradle” of Neandertal evolution, and anthropologists have theorized that climatic factors or competition from modern humans were the likely causes when Neandertals started disappearing around 30,000 years ago. But new research suggests that Western European Neandertals were on the verge of extinction long before modern humans showed up.

This 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.

“The Neandertals are our closest fossil relatives and abundant evidence of their lifeways and skeletal remains has been found at many sites across Europe and western Asia,” said Quam, assistant professor of anthropology. “Until modern humans arrived on the scene, it was widely thought that Europe had been populated by a relatively stable Neandertal population for hundreds of thousands of years. Our research suggests otherwise and, in light of these new results, this long-held theory now faces scrutiny.”

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 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 from Western Europe that were 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 not clear, but it may be possible to pinpoint it further with additional study.

“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 rethinking 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,” Quam said. “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.”

The results presented in the study are based entirely on degraded ancient DNA, and the analyses have therefore required advanced laboratory and computational methods. The research team includes statisticians, experts on modern DNA sequencing and paleoanthropologists from Sweden, Denmark, Spain and the United States.

“This is just the latest example of how studies of ancient DNA are providing new insights into an important and previously unknown part of Neandertal history,” Quam said. “Ancient DNA is complementary to anthropological studies focusing on the bony anatomy of the skeleton, and these kinds of results are only possible with ancient DNA studies. It’s exciting to think about what will turn up next.”

5 Responses to “DNA analysis shakes up Neandertal theories”

  1. Buzz Adams says:

    It would be interesting to see on a map the hypothetical populations compared to the ice cover in europe. It wouldn’t be to surprising to understand that no population could be found in periods where these areas were completely covered. If the severity of ice ages varied then perhaps the last one was just too big.

  2. Aurelius says:

    Is it not possible that with more inclement weather patterns, many Neandertals in European enclaves may have just shifted their ranges to more clement zones and the diminished mtDNA is a result of remnant populations breeding with those individuals left in their now colder home ranges? Would the persistence of Neandertals in these now harsher climactic zones not indicate adaptation? Changes such as the onset of a new harsher period in Ice-Age weather did not happen in one season. The indication of a diminished gene pool may just coincide with the new environments lack of ability to support populations as large as what once seemingly inhabited Europe. Less fauna equals less folks able to exploit available resources and greater land areas would most likely have been needed to support existing populations, or remnant populations. Yes, Neandertals as an individual species are now extinct, but as evidenced through genetic persistence of some Neandertal sequences (and now Denisovan genetics) in modern populations would their disappearance as a species indicate a failure or a triumph in hominin adaptability? On a cold, lonely night, by a campfire, it seems that a Neandertal, a Cro-Magnon, and why not add a Denisovan, found that their differences may not be not so great. Love this stuff. Many of us, it seems, are hybrids.

  3. mathieu gasc says:

    As usual any dna ‘discovery’ is higlighted in the news as the new insight into such and such. Nothing new under the sun, especially not kids toying with genes, claiming to be objective scientists. DNA study is so new and intricate that it might very well be a totally different set of approach defining it within a decade.
    Sometimes i wonder if journalists know a thing about human evolution and more particularly about neanderthal…
    The bottle neck theory has been discussed for a while, while the recovery is not really evidence by anything, only the arrival of sapiens, same old story… go take archaeology 101 gail glover.

  4. Tez says:

    I do not really see how generalisations about a very small local population can be applied when there is so little archeological evidence, for all we know they may have been an isolated tribe who practiced incest as there where no other non-related people nearby. This would obviously skew any DNA results.

  5. beej says:

    I’m just mulling over whether an epidemic of some sort may have been a factor in the depopulation, and a small group of survivors, protected by a mutation that provided immunity to a viable breeding population, or perhaps just geographically separate, subsequently expanded to fill the continent.

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