Neanderthals: Still in Our Genes?[
Neanderthals: Still in Our Genes?
Jennifer Viegas, Discovery News
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Aug. 22, 2006 — Individuals of European descent may be 5 percent Neanderthal, while West Africans could be related to an archaic human population, according to a recent study of genes of people from Yoruba and individuals living in Utah with ancestry from Northern and Western Europe.
Since both groups spread, the find suggests we all have a bit of archaic DNA in our genes. This counters the view that modern humans left Africa and replaced all other existing hominid populations.
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"Instead of a population that left Africa 100,000 years ago and replaced all other archaic human groups, we propose that this population interacted with another population that had been in Europe for much longer, maybe 400,000 years," co-author Vincent Plagnol told Discovery News.
Plagnol, a researcher in the Department of Molecular and Computational Biology at the University of Southern California, and colleague Jeffrey Wall analyzed patterns of ancestral linkage in 135 modern individuals.
Using statistics and computer modeling, they focused on linkage disequilibriums, or sections within genes that did not make sense if only modern human matings were considered. The missing genetic links only fit if some other hominid population was introduced into the model, according to the paper, which was published in PLoS Genetics.
"We considered the data from modern human DNA and fitted a model to explain what we see," explained Plagnol. "We found that a simple model cannot explain the data if we do not add an ‘ancestral population.’ If this population did not cross with modern humans — or almost did not — the effect is too small to explain the data. We find that a rate of 5 percent is what is needed to explain what we see."
The researchers agree with recent studies that concluded Neanderthals did not contribute any mitochondrial DNA — genetic material that is passed from mothers to children. However, they say other portions of the European genome, such as those associated with nuclear DNA, may still harbor the Neanderthal imprint.
Plagnol said different parts of the genome have different ancestry, so an individual could have a fraction of a certain chromosome that was inherited from a Neanderthal, but then possess "very typical homo sapiens mtDNA."
The scientists are not certain what early human group could have contributed to West African DNA, but both Europeans and Africans in the study showed about the same 5 percent archaic contribution. Neanderthals are believed to have originated in Africa around 400,000 years ago, but they left and then settled in Europe, hence the apparent lack of interaction with modern humans in Africa.
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Alan Templeton, of Washington University in St.Louis, also conducted DNA studies and came to similar conclusions.
"The humans who were in Africa and the humans who were in Eurasia were regularly interchanging genes," he said, "there was interbreeding and when humans came out of Africa 100,000 years ago they did not replace these other human populations in Eurasia."
New technologies are being developed to sequence nuclear DNA from fossils, so in the near future, scientists may learn more about how modern human genes compare with those of archaic humans, like Neanderthals.
