An Elusive Ancestor

Michael Marshall describes how the Denisovans – a now-extinct group of hominids known only through a single fragment of bone and a handful of teeth – may have been more far-reaching than the Neanderthals:

When Pääbo and Reich published the first Neanderthal genome, the big news was that on average 1.7 per cent of the DNA in modern people other than Africans comes from Neanderthals. In other words, our ancestors interbred. Did they also interbreed with Denisovans?

To find out, the geneticists looked at the few parts of the genome that vary from person to person, searching for individuals who carry Denisovan versions of these sections. Most of the people the sampled had no sign of Denisovan DNA, even if they were from mainland Asia, where our ancestors might have been expected to run into Denisovans. However, as part of the Neanderthal study, the researchers had sequenced the genome of someone from Papua New Guinea. “That was a fortuitous choice,” says Reich. “When you analysed the Papuan sequence, bang: you got this huge signal.” More comparisons showed that other Melanesian people also carried Denisovan DNA, with an average 4.8 per cent of their genome coming from Denisovans.

Clearly interbreeding did occur. But if Denisovans lived in southern Siberia, how on earth did their DNA wind up in Melanesia, thousands of kilometres away across open sea? The most obvious explanation is also the most startling: Denisovans ranged over a vast swathe of mainland Asia and also crossed the sea to Indonesia or the Philippines. That means they had a bigger range than the Neanderthals.

Previous Dish on the Denisovans here and here.