A new genetic study, published in the journal Genetics, supports the hypothesis that Neanderthals interbred with anatomically modern Homo sapiens in Eurasia.

Study co-author Dr Konrad Lohse from the University of Edinburgh explained: “our approach can distinguish between two subtly different scenarios that could explain the genetic similarities shared by Neanderthals and modern humans from Europe and Asia.”

The first scenario is that Neanderthals occasionally interbred with modern humans after they migrated out of Africa.

The alternative scenario is that the humans who left Africa evolved from the same ancestral subpopulation that had previously given rise to the Neanderthals.

Many anthropologists say the interbreeding scenario is more likely, because it fits the genetic patterns seen in studies that compared genomes from many modern humans.

By using only the information from one genome each of several types: Neanderthal, European/Asian, African and chimpanzee, Dr Lohse with colleagues completely ruled out the alternative scenario, revealing strong support for Neanderthal admixture in Eurasia at a higher rate (3.4-7.3 per cent) than suggested previously.

“Because the method makes maximum use of the information contained in individual genomes, it is particularly exciting for revealing the history of species that are rare or extinct.”

The method can more confidently detect the genetic signatures of interbreeding than previous approaches.

In fact, the researchers originally developed it while studying the history of insect populations in Europe and island species of pigs in South East Asia, some of which are extremely rare.

Dr Lohse also said the new method estimates a slightly higher genetic contribution of Neanderthals to modern humans than previous studies.

“Estimating this contribution is complex and is likely to vary slightly between different approaches.”

“This work is important because it closes a hole in the argument about whether Neanderthals interbred with humans,” said Editor-in-Chief of the journal Genetics Dr Mark Johnston, who was not involved in the study.

“And the method can be applied to understanding the evolutionary history of other organisms, including endangered species.”

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Konrad Lohse & Laurent A. F. Frantz. Neandertal Admixture in Eurasia Confirmed by Maximum Likelihood Analysis of Three Genomes. Genetics, published online February 13, 2014; doi: 10.1534/genetics.114.162396