More on European Neanderthals almost extinct before arrival of Modern Humans
|A Neanderthal mandible from Valdegoba, Spain, that yielded the DNA sequence researchers used to determine that Western European Neanderthals were on the verge of extinction long before modern humans showed up [Credit: Rolf Quam]|
"The Neanderthals are our closest fossil relatives and abundant evidence of their lifeways and skeletal remains have 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 Neanderthal 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 Neanderthal 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. Neanderthal 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, Neanderthal 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.
|Rolf Quam, a Binghamton University anthropologist, points out where the mandible came from in the stratigraphy of the Valdegoba cave in Spain [Credit: Rolf Quam]|
"The fact that Neanderthals 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 Neanderthals 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 Neanderthals.
"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 Neanderthal populations were already demographically stressed when modern humans showed up on the scene."
The results presented in the study are based entirely on severely degraded ancient DNA, and the analyses have therefore required both advanced laboratory and computational methods. The research team has involved experts from a number of countries, including 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 Neanderthal history, "said Quam. "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."
Source: Binghamton University, State University of New York via Newswise [March 24, 2012]