Recent genetic analysis of ancient bones suggest that modern humans encountered and bred with Neanderthals and Denisovans, two of the other human groups. Samples taken from the pinky finger of a girl from 40,000 years ago found in a Siberian cave and the oddly shaped molar of a young adult have wrought evidence to suggest that modern humans bred with them.
This poses a potential challenge to the ‘out of Africa’ theory that states that modern humans (Homo sapiens) evolved solely in Africa and left between 125,000 and 60,000 years ago to populate other parts of the planet. This new evidence suggests that modern humans left Africa along with the common ancestors of the Denisovans and Neanderthals and subsequently interbred to produce what could be called a ‘hybrid species’ – today’s Homo sapiens.
Recent scientific analysis has uncovered that today’s humans outside of Africa carry an average of about 2.5% Neanderthal DNA and that people from parts of Oceania also carry about 5% Denisovan DNA. In addition to their Neanderthal genes, Southeast Asians also carry approximately 1% Denisovan DNA. It is currently unknown whether the Denisovans and the Neanderthals interbred.
Though there is some conflict over this as Swiss geneticists Mathias Currat and Laurent Excoffier suggest in a recent paper that breeding between Neanderthals and humans was rare otherwise we would have a much higher frequency of Neanderthal DNA present today.
The value of such interbreeding aided survival of modern humans in Europe and Asia as the Neanderthals and Denisovans had lived there thousands of years prior to the arrival of Homo sapiens suggesting that they had donated immunity to diseases that we would not otherwise have (it remains in the modern genome today). While this DNA provided help with immunity it is thought that it is also responsible for a number of autoimmune disorders experienced today like that of diabetes, arthritis and multiple sclerosis.