That partial finger bone was the first evidence of the Denisovans, a distinct branch of the Homo family tree, whose members mated with both Neanderthals and modern humans during the past 100,000 years. Denisovans may have roamed vast expanses of Asia with tools as sophisticated as those made by modern humans at the time. But years have passed since the discovery of the Denisovans, and the only tangible evidence of them is still that pinky nub and three additional molars from the same cave.
The little finger belonged to someone who was still growing, but is otherwise nondescript. The molars are big — larger than those of any recent humans and within the range of pre-human Australopithecines who lived millions of years ago.
Aside from these scant clues, everything we know about Denisovans comes from their DNA. Never before has the history of an extinct human been told by its genome, rather than its fossils and artifacts. It’s “a new era in anthropology,” says Meyer.
Defined by their DNA
Meyer and his Max Planck colleagues have successfully extracted DNA from all four Denisovan fossils and determined that the specimens came from different individuals. Based on accumulated genetic differences among them, two of the individuals lived roughly 65,000 years before the others; the Denisovan lineage was around for quite some time.
Denisovans, Neanderthals and modern humans descend from the same population of ancestors, who most likely lived in Africa between 550,000 and 765,000 years ago. Some of these early humans spread to Eurasia, where they split into Neanderthals in Europe and Denisovans in Asia.
Denisovans were “like an Eastern cousin” of Neanderthals, says Meyer.
For some period after that initial dispersal, the human groups — now divided geographically — were evolving into distinct species. Had they stayed separated longer, they would have naturally accumulated too many genetic differences to mate successfully.