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YESTERDAY, THE DISCUSSION was on Neanderthals and Denisovans, branches of human evolution who didn’t quite make it. I also cited a mild preference for Denis as my given name. Today, we get the latest word on Denisonvans from Science magazine, the weekly publication of the American Association for the Advancement of Science.
The Latest Word. AAAS Science, September 20, 2019, brings Denisovan matters up to date with Michael Price’s “Face of Mysterious Denisovans Emerges.”
“Denisovans,” Michael Price writes, “ranged from Siberia to Southeast Asia and may have persisted until as recently as 30,000 years ago, based on their genetic legacy in living Southeast Asians.”
Denisovan fossils have been rare indeed: a girl’s pinkie bone and three teeth from Denisova Cave and a recently identified lower jaw from the Baishiya Karst Cave on the Tibetan Plateau.
In 2014, researchers introduced a novel means of analyzing gene regulation in long-extinct hominins. Price notes that a chemical modification called methylation allows tracking changes in an ancient genome. In this case, the ancient DNA came from the Denisovan girl’s pinkie.
A Database of Genetic Change. Then, Price describes, “To find out how Denisovans’ unique methylation patterns might have influenced their physical features, the researchers consulted the Human Phenotype Ontology database of genes known to cause specific anatomical changes in modern humans when they are missing or defective.”
The information is comparative, not quantifiable. For example, based on this girl’s DNA, researchers predicted that Denisovans had longer fingers than modern humans, for example. Price writes, “In total, the researchers discovered 56 Denisovan anatomical features that may have differed from humans or Neanderthals, 34 of them in the skull.”
The girl shares some Neanderthal characteristics, “a similarly flat cranium, protruding lower jaw, and sloping forehead…”
“Yet,” Price notes, “she also had key differences. The reconstructed face was notably wider than that of a modern human or Neanderthal, and the arch of teeth along the jawbone was longer.”
Theory and Reality. Remember, this research was based solely on the girl’s little finger. Yet, also recall that Denisovan lower jaw from the Tibetan Baishiya Karst Cave.
It turned out there was a close fit between the DNA-based reconstruction and the actual fossil: Price notes, “The jawbone was wider than that of either humans or Neanderthals, and there were hints that it protruded about as much as in Neanderthals but more than in modern humans.”
Of course, thus far the evidence is slight: a pinkie and a jaw bone, both likely Denisovan but found some 1400 miles apart. Price quotes a bioinformatician who said, “If you were to find a single Homo sapien fossil and it’s an NBA basketball player, then you might conclude that Homo sapiens were 7 feet tall. It’s an interesting approach but we can’t verify the predictions until several Denisovan skeletons are found.”
I may still drop that extra “n.” ds
© Denis Simanaitis, SimanaitisSays.com, 2019