New studies reveal 20 Percent of Neanderthal genome lives on in modern humans
Last year, ground-breaking research revealed conclusive evidence that Neanderthals bred with modern humans (Homo sapiens), a fact disputed for many years. The first ever complete mapping of a Neanderthal genome found that the genomes of people living outside Africa today are composed of some 1 to 4 percent Neanderthal DNA. Now two new studies suggest that, taken collectively, about 20 percent of Neanderthal DNA still lives on in modern humans, influencing the skin, hair, and diseases that people have today.
Two studies published concurrently in Nature and Science on Wednesday suggest that while the Neanderthal contribution to our genomes was modest, it may have proved vitally important. In fact, the features acquired from Neanderthals may have been what enabled modern humans to survive, for example, genes that conferred an advantage in local climatic conditions.
The research found that Neanderthal DNA is total absent from some parts of non-African genomes, while other regions abound with it. Joshua Akey, who led the study in Science, believes this may be because some genes were beneficial, while other genes would have caused problems in modern humans and were therefore weeded out over time.
In the Nature study, Sriram Sankararaman and David Reich of Harvard Medical School used the previously sequenced Neanderthal genome to screen 1,004 modern genomes for sequences with distinctive Neanderthal features.
In the Science study, Akey and Benjamin Vernot, both of the University of Washington in Seattle, used similar statistical features to search for Neanderthal DNA in the genomes of 665 living people—but they initially did so without the Neanderthal genome as a reference. They still managed to identify fragments that collectively amount to 20 percent of the full Neanderthal genome.
Despite their different approaches, both teams converged on similar results. They both found that genes involved in making keratin—the protein found in our skin, hair, and nails—are especially rich in Neanderthal DNA. For example, around 66% of East Asians contain the Neanderthal skin gene, while 70% of Europeans contain the Neanderthal gene which affects skin colour. Sankararaman also found Neanderthal variants in genes that affect the risk of several diseases, including lupus, biliary cirrhosis, Crohn's disease, and type 2 diabetes.
Both research groups also found some regions of the modern human genome that are totally void of Neanderthal DNA, including those involved in motor coordination, as well as areas involving the testes and the X chromosome. This suggests certain Neanderthal mutations were incompatible with modern humans and were removed during evolution, perhaps because they reduced fertility.
Uncovering mystery humans
Both research teams are now planning to apply their methods to other hominids like the Denisovans, and they are hoping this may enable them to unravel one of the greatest mysteries in the field of human origins to emerge last year.
Towards the end of 2013, studies revealed that the Denisovans share up to 8% of their genome with a “super archaic” and totally unknown species that dates back around 1 million years. It appears that the Denisovans bred with a mystery species from Asia – one that is neither human nor Neanderthal. Traces of the unknown new genome were detected in two teeth and a finger bone of a Denisovan. In fact, there were several studies last year which pointed to the fact that there is unknown species in our family tree that is yet to be identified.
The methods employed by the research teams may provide the first glimpse at this mystery species by enabling the partial reconstruction of genomes of unknown groups of ancient humans within the Denisovan DNA.
Advances in technology are truly changing our understanding of who we really are and our ancient origins.