This is the seventh of a series of posts I will be doing on human evolution. The previous one can be found here. As always, please leave any questions you’d like to have answered.
For quite some time scientists have known that there were three separate instances of hominids leaving Africa to settle the rest of the Old World. The ancestors of modern humans left about 60,000 years ago. The ancestors of Neandertals, about 500,000 years ago. And the first group to leave, Homo erectus, about 1.9 million years ago. These three migrations accounted for all of the diversity found in fossils throughout Europe and Asia. But now we know that there was a fourth group.
In April a team of researchers published a paper in Nature announcing the sequencing of DNA from a finger bone fragment found in the Altai Mountains in southern Siberia. The bone fragment had been dated to an age of 30 to 48 thousand years old, a time at which both modern humans and Neandertals were living in the region. Curious about which species the bone belonged to, the researchers decided to sequence its mitochondrial DNA.
Much to the surprise of the researchers, the mtDNA in the bone fragment was neither Neandertal nor human; it belonged to a different, unknown species. When they calculated the time at which the individual the bone fragment had belonged to shared a last common ancestor with modern humans, it was found to be 1 million years ago, 900,000 years too late for this to be a Homo erectus.
That means that this is fossil belongs to a newly discovered species of hominid whose ancestors left Africa about 1 million years ago. We do not know anything about them at this point; we have not been able to associate any other bones or tools with them yet. We have no idea what they looked like, how they behaved, or how they lived. All we have is a string of DNA.
For me, this story illustrates the power of modern science. A discovery like this would have been impossible 10 years ago. Without sequencing technology, we probably would never have known about this chapter in hominid history. But now we know this species lived and can go back to the fossil record looking for traces of it, traces we would never know belonged to another species without this genetic data.