Denisovans Had Fingers Indistinguishable From Modern Humans, Further Complicating Our Family Tree

The missing part of one of the most important fossils ever found has been identified, challenging ideas on modern humans' relationship to our nearest relatives.

In 2008 a finger bone was found in Denisova Cave in Siberia, and DNA extracted from it shocked anthropologists by revealing a new human relative. Beforehand, however, the bone was cut in two and sent to different laboratories. Records of these actions were lost and researchers thought the two pieces might be from different individuals. Since the cave is known to have been inhabited not only by the Denisovans, to whom it gave its name, but also Neanderthals, and one Denisovan/Neanderthal hybrid there were questions over the other fragment’s origins.

Now, however, the 50,000-year-old phalanx bone has been confirmed as being the other part of Denisova 3, the specimen that alerted the world to the Denisovans. Matching the two pieces together reveals a finger whose shape is well within the range of modern humans, while being recognizably different from that of Neanderthals.

A team led by Dr Eva-Maria Geigl of University Paris Diderot extracted DNA from the second fragment. In Science Advances, they report an exact match with the previously sequenced DNA, as well as showing the two parts of the bone fit together.

Once reconstructed by computer modeling, the similarity of the phalanx’s shape to our own is surprising, because Neanderthals and Denisovans are thought to be more closely related to each other than to anyone alive today. It also means palaeontologists finding Denisovan finger bones – and perhaps other parts – might not realize what they have, thinking this is just another bone from an ancestral modern human.

Reconstruction of the fingerbone that provides most of what we know about Denisovans from two angles. The blue is computer modeling of the section from which extracted DNA alerted the world to their existence, and the brown is the newly identified section now matched to it, Bennett et al/Science Advances

Denisovans were among the closest relatives of humans living today, yet everything we know about them comes from just a (literal) handful of bones, making these perhaps the most precious fossils in existence. We know they inhabited parts of East Asia for hundreds of thousands of years. They interbred with out ancestors to leave their genetic mark in humans today, bequeathing Tibetans the genes to live at high altitude and shaping the immune systems of more than a billion people.

The nucleic genome extracted from this Denisovan fingerbone placed them as a break-away from Neanderthals 410,000 years ago, with the two much closer to each other than either was to us.

Consequently, archaeologists have anticipated Denisovan anatomy would resemble Neanderthals. The Denisovan teeth that make up most of the rest of our fossil record of them resemble much older human species like Homo erectus.

However, if Denisovan fingers resemble our own, other parts may also be similar, changing what we should be looking for when seeking further specimens, and raising the question just how close to us these people really were.