Lurking deep in your DNA, you may have a ghostly remnant from a “super-archaic” protohuman that isn’t our ancestor. This is because over half a million years ago, “Neandersovans” – the common ancestor of Neanderthals and Denisovans – intermixed with a small-brained, super-archaic hominin. Hundreds of thousands of years later, Denisovans did it again. And after that, Neanderthals and Denisovans intermixed with ancestors of modern humans. Got it?
The ape-ish super-archaic was only distantly related to other Homo species, having split off from the Homo family tree about 2 million years ago. Going by the indirect evidence of the admixture, this creature with a brain the size of an orange evidently survived to grunt the tale for well over 1.5 million years.
These early mixing-and-matchings were deduced by Alan Rogers, Nathan Harris and Alan Achenbach from the University of Utah, based on an innovative analytic technique they call “Legofit” – the results of which were published Thursday in Science Advances.
The mating between the Neandersovans and the mystery super-archaic is the earliest known episode of gene flow in the human line, the authors say. Yet again, we discover that multiple human species coexisted, overlapping in time and space. While the mechanism of the interspecies attraction remains a mystery, it is starting to seem that different human species lost no opportunity to mate with each other. Or maybe they took whatever opportunity beckoned.
Population and group sizes of the super-archaic hominin is believed to have been small: They had migrated from Africa to a radically different environment and were “basically African apes trying to make a living in that environment,” Rogers describes.
Neandersovans had big brains, and so of course did their descendants the Denisovans. Yet if their sex-partner had split from the Homo tree 2 million years ago, wouldn’t it have had a very small brain? “I presume so, but I’ve never seen one,” Rogers laughs in conversation with Haaretz. “Judging by the time frame, they must have been much smaller than ours.”
To get this argument out of the way, are Neanderthals, Denisovans and We in fact separate species? Theoretically, because we interbred and had fertile offspring, we’re all the same species (albeit different types). By that criterion, this 2-million-year-old demi-ape is also the same species, though whether it could have fruitfully interbred with us today is an open question. For the purposes of clarity, we shall call each one a species.