Denisovans — Fossils, Genetics, Artifacts, & Speculation

November 6, 2016 in Fossils, Humans

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(This article is actually the second part of the Neanderthals & Denisovans — Who Were They? Comparison Of Evidence Against Pop-Culture Projection article, that had to be split because of length. Head over to that article for the preface and further information.)

The “Denisovans” receive their name from the Denisova Cave located in south-western Siberia, in the Altai Mountains. The cave itself has received its modern name owing to a Russian hermit by the name of Denis that lived there in the 1700s.

While the cave had been explored before, it wasn’t until 2008, when Michael Shunkov from the Russian Academy of Sciences and other Russian archaeologists from the Institute of Archaeology and Ethnology of Novosibirsk explored the cave, that hominid remains were found.

Altai Denisovans cave denisova

To be particular, in addition to artifacts, including a bracelet, the finger bone of a juvenile hominin was discovered. The artifacts were dated using radiocarbon and oxygen isotopes to sometime around 40,000 Before Present. A bone needle found at the site at a later point has been dated back to 50,000 BP — making it the oldest needle yet found anywhere in the world.

Excavations since then have revealed that hominid activity, which was apparently intermittent in the cave, goes back at least 125,000 years.

The above mentioned finger bone, when the mtDNA extracted from it was sequenced by Johannes Krause and Svante Pääbo from the Max Planck Institute for Evolutionary Anthropology amongst others, revealed some interesting things.

The juvenile female in question wasn’t that closely related to either homo sapiens, or to neanderthals. Going by the findings of that analysis (some recent analyses contradict this somewhat) the last time that modern humans, and Neanderthals + Denisovans, shared a common ancestor was probably around a million years ago. (Research since then has shown that there was clearly some interbreeding going on.)

Bracelet Denisovans jewelry

For those wondering about the preservation of 40,000-year-old DNA — this is largely down to the very cool climate of the cave, where the average annual temperature lingers around 0° Celsius.

“The mtDNA analysis further suggested that this new hominin species was the result of an earlier migration out of Africa, distinct from the later out-of-Africa migrations associated with modern humans, but also distinct from the earlier African exodus of Homo erectus. Pääbo noted that the existence of this distant branch creates a much more complex picture of humankind during the Late Pleistocene. This work shows that the Denisovans were actually a sister group to the Neanderthals, branching off from the human lineage 600,000 years ago.”

As far as what Denisovans looked like? As complete skeletal remains have not been found, there’s not much to go on. A finger bone that is much broader and more robust than what’s seen in any modern humans (interestingly it’s a female’s finger bone); a toe bone (that seems to have belonged to an individual of mixed Denisovan-human parentage that lived 100,000 years ago); and a tooth that “shares no derived morphological features with Neanderthal or modern humans.”

The finger bone morphology suggests that they were likely of robust and very strong build, as the Neanderthals were.

Denisovans fossil bone finger

To explain that — human skeletal density, and connective tissue extent/robustness, have decreased significantly over the last few tens of millennia, in particular since the agricultural boom began some 10,000 years ago. Judging by differences between humans and chimpanzees (our closest relative), this seems to also have been accompanied by a diminishing of innervation and associated brain control/access of physicality. Anyone who’s worked with wild chimpanzees is likely aware of how much stronger a male chimpanzee is than a male human of the same weight/size.

And, to be clear, the comparison that I’m talking about is that of “high-level” athletes versus normal wild chimpanzees. While (human) strength athletes (power-lifting, etc) may indeed look larger, and carry more muscle mass, they are generally considerably weaker across all parameters than wild chimpanzees of much lower weight. These differences are relatively subtle ones of: neurology, muscular structure, skeletal structure, connective tissue structure, and mental access.

A similar truth holds with the so-called Neanderthals, and no doubt many other earlier hominids. Neanderthals, for instance, were much more robustly built throughout the arm and shoulder regions — possibly at the expense of shoulder flexibility, though this is open for debate somewhat. (There is quite a lot of variation amongst modern humans with regard to shoulder structure/flexibility.)

Oldest needle Denisovan tool

Denisovan Genome & Genetics

Denisovans have left some of their genetics behind in some modern human populations. Melanesians and Australian Aboriginals, along with some peoples in southern India, in particular have high quantities (~3-5%).

Denisovans seem to have lived throughout different parts of Eurasia, at different points in time. The mitochondrial DNA from a 400,000-year-old hominin femur bone found in Spain, for instance, proved that the bone, previously thought to have been either Neanderthal or Homo heidelbergensis, was closer to Denisovan mtDNA than to Neanderthal mtDNA.

Very interestingly, ethnic Tibetans apparently possess a region of DNA, haplotype, around the EPAS1 gene that assists with adaptation to low oxygen levels at high altitude, that recent research has shown was found in the Denisovan genome.

As with Neanderthals, roughly 8% of the Denisovan genome seems to be derived from mysterious unknown hominid species that the Denisovan’s ancestors apparently interbreed with some 1 million years ago in Asia. Presumably some of the descendants of earlier “homo erectus” migrations into Asia, but who knows.

Denisovans fossil tooth Altai

Denisova cave Altai Mountain range

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