The Earth of about 80,000 years ago must have been a pretty interesting place. That’s the point in time when our direct human ancestors left the African continent and began to spread across the face of the globe. As they spread, they encountered hominid cousins–cousins so closely related that, from time to time, our direct ancestors were able to interbreed with them and produce live, fertile offspring who, in turn, produced other children who entered into the ancient human genetic mix.
We know all of this because of the work performed in the human genome project, which is hard at work in analyzing human DNA and tracing it back to sources. The human genome project has shown that our DNA includes elements from Neanderthals, like the thoughtful fellow pictured above, and Denisovans. Now the project has identified a third, previously unknown, and as-yet-unnamed ancestor species that left an imprint on our DNA. The unknown species might be a product of separate interbreeding between Neanderthals and Denisovans or might be an entirely separate species.
Neanderthals, Denisovans, and the third species are now extinct, but they live on in their fractional contributions to our DNA, with most modern Europeans and Asians carrying a tiny part of Neanderthal DNA and most Melanesians and Australian Aboriginals carrying slightly larger amounts of Denisovan DNA. Researchers are trying to figure out what meaningful impact–if any–this “archaic DNA” has on the appearance, immune systems, and other characteristics of humans. That’s a complicated process, and the fact that we’ve now identified and welcomed to the human family another, previously unknown ancestor just makes the puzzle more challenging.