New study leaves little room for doubt – Neanderthals and humans interbred
In recent months, numerous DNA studies of ancient humans have all converged on one conclusion – Neanderthals and Homo sapiens interbred. While for many this may seem unsurprising or even obvious, we must remember that until fairly recently the predominant scientific theory was that Neanderthals and Homo sapiens never came in contact with each other, let alone interbreed. Science is also only just beginning to dispel the myth that Neanderthals were primitive cave men. But for some, the idea that up to 20% of Neanderthal genes are still present in the human race is still very hard to swallow. However, a new study , which utilised a more superior method of testing, leaves little room for doubt – many human beings alive today are the product of Neanderthal and Homo sapiens interbreeding.
The new research published in the April 2014 issue of the journal Genetics has utilised a technique that involves partitioning genomes into short blocks to calculate the statistical likelihood of distant or recent interbreeding and tracing back the biological ties that exist between humans and Neanderthals. The method can more confidently detect the genetic signatures of interbreeding than previous approaches, and has further enabled the researchers to distinguish between two possible scenarios – the first is that Neanderthals occasionally interbred with modern humans after they migrated out of Africa, the second is that the humans who left Africa evolved from the same ancestral subpopulation that had previously given rise to Neanderthals.
“Although there has been mounting evidence for genetic exchange between modern humans and Neanderthals in Eurasia from a number of recent genetic studies, it has been difficult to rule out ancestral structure in Africa,” said study co-author Dr Konrad Lohse, a population geneticist at the University of Edinburgh. "Our approach can distinguish between two subtly different scenarios”.
The researchers found that evolution from the same ancestral population could be completely ruled out: “Our analysis allows us to conclusively reject a model of ancestral structure in Africa and instead reveals strong support for Neanderthal admixture in Eurasia at a higher rate (3.4% - 7.3%) than suggested previously,” wrote the study authors. Furthermore, the results demonstrate that “secondary admixture from Neanderthals into Eurasians took place after the expansion of modern humans out of Africa”.
The same method will be useful in other studies of interbreeding where limited samples are available. "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," said Lohse.
"This work is important because it closes a hole in the argument about whether Neanderthals interbred with humans. And the method can be applied to understanding the evolutionary history of other organisms, including endangered species," said Mark Johnston, Editor-in-Chief of the journal Genetics.