Convoluted human evolution: Denisovans may be three (Introduction)

by David Turell @, Friday, April 12, 2019, 22:48 (68 days ago) @ David Turell

DNA work has turned up that Denisovan 'types' Are found in several places:

"a new study using genetic data is offering an intriguing new look into the history of the Denisovans, revealing them as a people of far greater diversity, and reach, than ever before.
The now-extinct people that we call Denisovans actually consisted of three distinct groups of humans spread throughout Eurasia, the researchers say. And one of those groups might well even be considered its own species.

"recent work, including the sequencing of their genome, has begun to peel back the layers of mystery. The Denisovans, along with the Neanderthals, were part of a branch of humans that diverged from our own lineage somewhere between 500,000 and 700,000 years ago. They inhabited Eurasia for hundreds of thousands of years, reaching from Siberia far into tropical Indonesia, and they interbred with both Neanderthals and modern humans.


"Previous studies have shown that Southeast Asians — and Pacific Islanders in particular — have a greater proportion of Denisovan DNA than the rest of us. These researchers confirmed that finding, but the breadth of their data also allowed them to go a step further. Pairing their evidence with geographic and demographic data, they used the modern-day fragments of Denisovan DNA to reconstruct what those ancient populations actually looked like.

"The result is a trove of data on the ancient hominins, one that substantially deepens our understanding of their lives writ large. But the find is no lucky break — Denisovan DNA has been lurking in the genomes of Indonesians and others in Southeast Asia all along. Up until now, though, Western scientists hadn’t thought to look.


"In some modern Indonesians, scientists found not one, but two distinct Denisovan genomic signatures. What’s more, these two groups also looked different from the Denisovans previously found in Siberia, which they researchers say was another group altogether. For those of you keeping count, that adds up to three different kinds of Denisovans spread from Siberia to across the disparate islands of Indonesia.

"It’s a substantial expansion of Denisovans’ range. Whereas scientists published evidence proving they lived in just one small cave in 2010, we now know that Denisovans ranged across thousands of miles during their time on Earth. Being spread across so wide and area for so long probably played a role in the Denisovans’ eventual diversification.

"The three groups were bounded by two large geographical impediments: the Himalayas in the east, and the oceanic gaps between the islands that make up Indonesia today. As the researchers see it, one group of Denisovans would have lived in or around present day Siberia, Kazakhstan and in China just north of the Himalayas. And the remains from members of this group are likely what researchers found in 2010. But a different group of Denisovans lived in Southeast Asia, around present day Thailand and Vietnam. The third group called the islands of Indonesia home. Those two southern groups diverged from the Siberian Denisovans over 250,000 years ago. That’s before anatomically-modern humans even appeared.


"One of the groups that showed up in the Papuan’s genomes actually looked so genetically distinct that Cox says they should likely be considered an entirely new species. While the researchers cannot name a new species without actual fossil evidence, Cox says that, genetically, the group living in south-east Asia looked as different from the Denisovans in Siberia as it did from Neanderthals.

“'If we’re going to call Neanderthals and Denisovans by a unique name, which we do, then we should probably call this other group by another name,” he says.

"The concept of “species” among ancient hominins is a bit difficult to define — after all, they could often produce fertile offspring with each other, violating a common definition of a species. But, by the current nomenclature, these Denisovans would have been as distinct as other groups of hominins that we call species. If so, it would add yet another branch to the still-growing evolutionary tree of ancient humans.

"Finding the Denisovans spread across so much territory, and inhabiting such different environments, should also notch up our regard for Denisovans’ abilities, Cox says.
“They must have been able to do water crossings, so they must have had some sort of rafts or canoes. We know that they lived across a wide range of environments, from up in Siberia where it freezes during the winter all the way down to tropical rainforests,” he says. “So they must have been incredibly adaptive.”

"Indeed, the Denisovans lived for hundreds of thousands of years in territories where modern humans are today, and they survived for longer than our own species has existed. They were numerous and geographically diffuse enough to birth what is likely an entirely new species of human, and they and our ancestors managed to live in close proximity to each other for tens of thousands of years."

Comment: After surviving so long, there should be fossils to help us understand.

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