Mysterious DNA Found Within African Population

On Wednesday, experts reported the discovery of evidence of a branch of humans that existed a million years ago, now extinct. The evidence of these early humans was found in the DNA of people from West Africa. The discovery, made by two geneticists at the University of California, Los Angeles, may help scientists decipher early human genetic variation.

To understand where these ancient humans come into play, we need to have a short anthropology lesson, starring a few key players. There’s us, Homo sapiens. Then there are our close relatives Homo neanderthalensis, or Neanderthals. Very closely related to the Neanderthals are the Homo Denisova or the Denisovans.

All of us Homos originated from Africa. But around 600,000 years ago, the common ancestors of ours, split into two groups; one group stayed in Africa, and the other moved north into Eurasia. This second group is called Homo heidelbergensis. After some time, H. heidelbergensis split, resulting in Neanderthals moving west and Denisovans moving east.

Meanwhile, back in Africa, modern humans evolved. They began to move into Eurasia and consequently interbred with the Neanderthals and Denisovans. By 40,000 years ago both Neanderthals and Denisovans were extinct, having been wiped out by a combination of environmental factors as well as having to compete with their African cousins for space and resources. Those that didn’t die in the harsh and competitive Pleistocene conditions are thought to have interbred with their new neighbors.

As a result, everyone today who is from outside of Africa has some amount of Neanderthal DNA in their genome. Additionally, Aboriginal Australians and New Guineans have Denisovan DNA. Recent evidence suggests that there may have even been smaller groups of both modern humans and Neanderthals that traveled and mixed genes before the large migration, which suggests that Neanderthal DNA is widespread and worldwide.

Dr. Sriram Sankararaman and Mr. Arun Durvasula are the geneticists at UCLA who made the discovery. For their study, they tracked new variations in genes among early living humans, early humans, Neanderthals, and Denisovans. Most of their data reflected current hypotheses about human evolution, but in a few West African populations, they found some variants not contained in any other living humans. Compared to Neanderthal and Denisovan DNA, there was no match.

Mr. Durvasula and Dr. Sankararaman’s data suggests this population split as long as a million years ago. They estimate this archaic population interbred and thus integrated with early West African humans 50,000 years ago. They could not say what the species of humans this enigmatic population was. There are lots of hominid fossils from Africa, and they don’t exactly make things clearer.

Dr. Sankararaman says he looks forward to testing the DNA of some of these fossils and comparing it to this mysterious population. Getting DNA from fossils is difficult, especially in the tropics, where DNA degrades faster because of the heat. Nonetheless, he’s hopeful DNA testing on fossils may reveal some insight into our human origins.