Extinct species of human found lurking in genes of West Africans

California: A new study comparing the genomes of 405 West African people to Neanderthal and Denisovan sequences has revealed the “ghost” of a mysterious and previously unknown hominin that once lived alongside our ancestors.

The study, by Arun Durvasula and Sriram Sankararaman of the University of California, Los Angeles, published this week in the journal Science Advance, sequenced the genomes of people from four modern West African populations.

After feeding the detailed data into very powerful computers, and then cross-examining and comparing them to Neanderthal and Denisovan sequences (as well as other modern African genomes) a spectral presence faintly revealed itself. Hidden deep in the DNA code of present-day humans is evidence of an extinct human species, detectable only by a few tell-tale genetic markers lingering in their ancestors. 

The study’s authors say that these genetic differences are best explained by hybridisation with an unknown humanoid. This suggests that ancestors of modern West Africans interbred with a yet-undiscovered species of archaic human – similar to how ancient Europeans mated with Neanderthals. 

Once, many species of humans roamed the Earth, of which Homo sapiens was just one. In 2014 a landmark genetic study revealed that human beings of European and Asian descent are not entirely human, as we had previously understood the term. That is, they are partial hybrids of at least three human species: Homo sapiens, Neanderthals and Denisovans. Denisovan DNA seems to be mostly found in Oceanian and some East-Asian populations, but basically everyone except sub-Saharan Africans has some Neanderthal DNA lingering in their cells, around 4 percent on average.

The researchers believe that the ancestors of this unknown archaic “ghost” hominin branched off from the modern human family tree before Neanderthals did. They even seem to have left their mark in modern populations to an even greater extent than Neanderthals: the amount of ‘ghost’ DNA in modern West African people ranged from 2 to 19 percent.

With the help of mathematical models and computer-aided number crunching, the team estimates that this archaic hominin split off from the ancestor of Neanderthals and modern humans between 360,000 and 1 million years ago. Then, from about 124,000 years ago, that break-off hominin reunited with the ancestors of modern West Africans and interbred with them, for an unknown period of time. They believe that the population of this introgressing hominin group was about 25,000 strong.

Although this is a simplified version of events – the separating and admixture of different populations and sub-species can be extremely muddled and complex – this is the most likely scenario that can be pieced together from the limited evidence. 

AlamulKhabar Sc & Health