Denisovan Finger Muddies Picture of Human Evolution

Lost fragment of the finger on which the discovery of the whole Denisovan species was based resurfaced, was measured, and everybody was in for a big surprise

Replica of a Denisovan finger bone fragment, originally found in Denisova Cave in 2008, at the Museum of Natural Sciences
Thilo Parg

berkeleThe more we learn about human evolution, the cloudier our chronicle becomes. The latest broadside from science is that even though the Denisovans’ teeth and jaws looked archaic, similar to Homo erectus or even maybe australopithecine — their fingers were just like ours.

Denisovan fingers were gracile like those of modern humans, explains Prof. Eva-Maria Geigl of Institute Jacques Monod, University of Paris, and not stubby digits with blunt ends like those of their sister species the Neanderthals.

“Denisovans had fingers indistinguishable from modern humans,” the team reported Wednesday in Nature.

This blast from the karst is based on thorough measurements of one bit of finger bone found in the famed Denisova Cave, but it writ volumes.

To be accurate, the original finger bone found in Denisova Cave had been cut in two for analysis by different teams; one part underwent what it underwent at the Max Planck Institute in Germany, and the other, bigger piece was misplaced, but ultimately sent to the University of California, Berkeley and finally to her lab, says Geigl, who did the research with colleagues from her own team as well as from the University of Bordeaux and the University of Toronto.

Prior to genomic analysis, Geigl measured and photographed the finger fragment. The mitochondrial genome produced in her lab was identical to the one that had yielded the genome in 2010 and 2012 confirming that  it was the missing part of the phalanx (finger bone). The bone fragment itself was then given back to Berkeley.

When science took the picture of the larger piece and the 3D scan of its small basis and reunited them virtually, science could for the first time meticulously analyze what a post-cranial body part of a Denisovan looked like. Science could compare this finger with those of modern humans and Neanderthals. And science was mightily surprised.

Entrance to Denisova cave
Igor Boshin / Shutterstock.com

That Denisovan touch

The existence of an unknown Homo species that came to be called the Denisovans was discovered in 2010 through the genetic analysis of a tiny fragment of finger bone found in Denisova Cave, in the Altai Mountains.

The finger turned out to belong to an unknown species of archaic human that was neither Neanderthal nor Homo sapiens.

Almost a decade later, definitely-Denisovan remains have been found in exactly two spots, no more: That cave; and 2,400 kilometers (about 1,500 miles) away on the Tibetan Plateau, where a jaw with some teeth was reported found in May. (It bears adding that among the extremely rare bits and bobs of hominin skeleton found in Eurasia, others — even many others — may also be Denisovan, but there’s no proof.)

So that's it. All we have from our long-gone forebears are a few teeth, a finger whose parts have now been reunited, and the jaw from Siberia and Tibet. Yet genetic analyses of those teeth, and deduction, have led to the postulation that Denisovans ranged all over Southeastern Asia. A major contributor to that theory is the discovery that today's Melanesians have high proportions of Denisovan genes, 4% to 6%, and Tibetans and the original settlers of Australia, the Aborigines, also have a clear Denisovan mark.

Genetic analyses suggest that proto-Neanderthals and precursor-Homo sapiens split about 700,000 years ago (argument over the exact date rages on). Then the ancestral Neanderthal line in Europe itself split around 400,000 years ago, into Neanderthals in the West and Denisovans in the East.

Despite their split and speciation, Neanderthals and Denisovans coexisted and mixed in some places — a lot — including in Denisova Cave itself. There, archaeologists identified a long bone aged 90,000 years as belonging to a first-generation Neanderthal-Denisovan hybrid teenage girl.

A Denisovan molar, found in Denisova Cave in 2000.
Thilo Parg

A separate study conservatively estimated that Denisovans lived in the cave 287,000 to 55,000 years ago, and that Neanderthals lived there during at least two points in prehistory: around 193,000 and 97,000 years ago.

As they ranged over Asia, the Denisovans themselves apparently split too. Based on diverging traces of Denisovan ancestry in our own genes, scientists deduce that there had been at least two distinct populations of Denisovans.

All this has led to much futile argument about whether we Homo sapiens sapiens are the same species as Denisovans and Neanderthals, given that we could and did interbreed, and also merrily mated with a host of other hominins. Geigl, a geneticist by profession, does not advocate for the separate-species camp. For what it’s worth, we did mix with them and there were profound morphological differences.

But what did the Denisovans look like? All we have of them is three teeth from Denisova Cave and the mandible discovered in Tibet. We cannot reconstruct either face or body.

All we can say is: The Denisovan jaw is not like ours. No DNA has been extracted from that ancient mandible), but that said, its form is archaic, retaining some characteristics of Homo erectus and some Neanderthal traits. Denisovan teeth are bigger than ours and more archaic.

“From this, one could have expected the finger bone — the only post-cranial skeletal element ever found of the Denisovans — to be archaic too,” says Geigl. But it wasn’t. “To our surprise, it’s like Homo sapiens’,” she tells Haaretz. Ergo, the Denisovan is a mosaic of primitive and advanced features.

All this information about the Denisovan finger leads to a new postulation not about Denisovans or us, but Neanderthals.

Newfound phalanx fragment shows Denisovans closer to modern humans than Neanderthals
Eva-Maria Geigl, Institut Jacques Monod,

To wit, maybe we and the Denisovans are the ones who retain an archaic morphology, of gracile fingers. More archaic forms of hominins seem to have had the same kind of slender digits that we do. Possibly the Neanderthal fingers evolved in a different direction, Geigl suggests.

But is it art?

Apropos fingers and dexterity, bone points and tooth pendants found in Denisova Cave were dated to 49,000 and 43,000 years ago — which, according to the timelines of Denisovan and Neanderthal occupation, suggests they were made by Denisovans. Bone points are thought to have been used in fashioning clothes, by simply poking holes in hide, through which some sort of fiber would be threaded.

These bone points and tooth pendants would be thousands of years older than, for instance, the famed Venus of Hohle Fels made of mammoth ivory that was found in Germany — which dates to perhaps 40,000 to 35,000 years ago.

In other words, the artifacts found in Denisova Cave may be the oldest known artifacts in Europe. Beyond Europe, it bears adding, we could count the 100,000-year-old beads (specifically, seashells with puncture holes) found in Skhul, Israel. The jury remains thoroughly out on the "Venus of Berekhat Ram", Israel, which dates to a quarter-million years ago but could be a pebble with vaguely mammarian protuberances, not a statuette.

Given new theories that early Homo sapiens ranged farther and wider than we had thought, and did so earlier than thought, we don’t know who made those bone points and pendants in Siberia. But the thought that the artisans were Denisovan is intriguing — especially as “Neanderthal art” found in Europe may be no such thing.

Earlier this year, 200,000-year-old teeth found in Yanhui Cave in Tongzi, southern China, just served to confuse things further. These teeth were not from Homo erectus or Neanderthals, but who they might have been from remains unknown.

The bottom line is that the paleontologists frenetically combing Eurasia in search of Denisovan remains may have been barking up the wrong trees if they were looking for archaic features in hominin fossils, Geigl points out.

“They would be well advised to look for other features too,” she sums up. The discovery also tells us something about continuity in some features — namely, the girth of our digits. And why might the Neanderthals have evolved more robust fingers? Who knows, perhaps environmental issues.