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Thursday, December 29, 2011

The Denisovans and the mystery of blonde hair…

Yeah, we know about Neanderthal and Homo Floresiensis but who the hell were the Denisovans?!
The Denisovans and the mystery of blonde hair…
Ethnic monitoring forms could be about to get even more complicated – that’s if you consider the whole of your ancestry to be important. Before paleogeneticists Svante Pääbo, and David Riech and the team at the Max Planck Institute for Evolutionary Anthropology decoded hominidae genomes of the living (humans and great apes) and the extinct (Neanderthal and Denisovan) the “Single-origin model”, of human evolution was popular with several scientists such as, paleoanthropologist
Chris Stringer and geneticist Brian Sykes. Neanderthal and Cro-Magnon were thought of as biologically separate species, unable to breed and produce viable hybrids. But in Stringer’s new book, The Origin of our Species and again during his recent talk at the Royal Institute, Stringer declared he was wrong about the “single-origin model”. (But neither does he fully support the multi-regional hypothesis) A band of Early Homo sapiens migrating out of Africa between 100,000 to 60,000 years ago, didn’t simply replace independently evolved populations from earlier out-of-Africa exoduses, (such as the Neanderthal), they bred with them. Many would convincingly argue the once controversial "multiregional hypothesis" is now proven by DNA evidence. And “Rhodesian Man” and “Iwo Eleru” fossils are no longer confusing anomalies. Stringer, head of Human Origins at the Natural History Museum, is an accessible, modest and world-class academic and clearly inspired by the fossils and the new DNA data that has proved him wrong.

Populations of people outside of Africa have far less genetic diversity than modern Africans, but they carry approximately 2.5% Neanderthal DNA - but not the same 2.5 of genetic material. Thus, which modern non-African regional groups inherited what particular Neanderthal genes and under what selection pressures and what benefit those genes give, if any, remains to be determined. DNA is best preserved cold, the small Siberian Denisovan fossils yielded both mitochondrial and autosomnal DNA. Denisovan Mitochondrial DNA analysis shows the shared ancestor of modern humans, Denisovans and Neanderthal lived 1M years ago, whereas the Mitochondrial ancestor of Neanderthal and modern humans lived 500,000 years ago. Both Homo heidelbergensis and Antecessor split and speciated away from their Homo Erectus origins around 1.5 million years ago. It is possible that H. heidelbergensis gave rise to Neanderthal and the Denisovans were a hybrid of Antecessor and early Neanderthal. The Denisovan morphology (a very large molar was found) and their genome suggests these were a robust and archaic-looking people. Yet they made tools and ornaments (before the Denisovan fossil discovery artifacts of this sort were attributed to modern humans) and were living in Southern Siberia up until at least 30,000 years ago.

Lake Baikol in Southern Siberia, largest freshwater lake in the world.
Denisovans colonised vast areas of East Asia, whereas Neanderthal populated Western Asia and Europe. When anatomically modern humans migrated from Africa they subsequently met and bred with the Neanderthal, somewhere around 60,000 years ago and those that went East subsequently met and successfully bred with the Denisovans – people with regions of their genome more similar to a chimpanzee than a Neanderthal. Some of these hybridised archaic people continued Eastwards and around 40,000 years ago became the early Melanesian (and probably Australasian) settlers. Thus, today’s Melanesians have 7.5% archaic genes, approx 2.5 Neanderthal and 5% Denisovan. This would help to explain the Australian 10,000yr old Kow Swamp skull’s archaic robusticity. Tests of Tasmanian bones are now important for future sampling.

Tasmanian Aboriginies

The YALI tribe of Papua New Guinea are believed to be direct descendents of the Denisovans.
Yali man Papua New Guinea
DNA from late populations of Southern European Neanderthal show they had evolved genes for red hair and fair skin. Some Melanesians and the Australian Aborigine are blond, in the pre-genetic-testing past this pigmentation confounded anthropologists. It was wrongly assumed Dutch sailors had left behind their genetic admixture for blond pigment. But as these groups exhibit a combination of blond hair and dark skin this theory was always doubted. I wondered if the Denisovans might have been blondes? At the Max Plank Institute pigmentation is not a major interest and they have not pursued this particular line of research, so, we must wait for another team to take up this challenge.

Blond hair is frequnetly seen in Melanesian children

African Bushmen (particularly groups that use a “click” in their language), also appear to carry archaic DNA. It’s possible some Erectus groups did not evolve into Heidelbergensis or Antecessor and, in turn, some of these did not evolve into Homo sapiens. Some isolated groups had a slower development and remained in confined regions of Africa, but were opportunist breeders when they encountered others, including emerging anatomically modern Africans. The archaic looking but recent “Iwo Eleru” fossil from Nigeria suggests hybridisation of archaic and emerging moderns continued up to as recently as 10,000 years ago. The “Rhodensian Man” specimen is 200,000 years old, (Homo sapiens Mitochondrial Eve lived 150,000 year ago) yet this fossil has the robusticity of a 2M year old H. erectus. Speciation of our direct ancestors away from archaic chimps took some 4 million years from approximately 9M to 5M yrs ago. Hybrids were born and they mated with both our ancestors and ancestral chimps giving rise to various Australopithecines. Stringer now believes that diverse ancestral groups developed in separate niches, 120,000 years ago the Sahara supported oases of grassland and interconnected rivers leading to the Mediterranean. It’s possible some relic populations of Australopithecines also held on in isolated regions. Homo floresiensis (Hobbit) is now thought to be an australopithecine and may be re-classified, even though these dinky bipeds had human faces, sailed boats, made tools, made fire, hunted co-operatively and lived as recently as 17,000 years ago.

Hobbit skull next to modern human skull and an artist impression of the Hobbit

There is no doubt that Africa is the continent of our origin, but the story of human evolution is complex, involving the hybridization of several highly divergent lineages. Stringer pays homage to Darwin in the naming of his book, but at the close of his Ri lecture Stringer commented, “As there seems to be archaic DNA input into all modern humans, even within Africa, I possibly should have called the book, ‘Origins of our Species’, instead of ‘Origin’.”

Below artist impressions of the multi-regional bushy hominid lineage and a Denisovan
Denisovan/Melanesian admixture in a Polynesian princess

I'm going to push the boat out here a little bit further and say that odd accounts of supposed proto-humans such as "Zana" require modern DNA testing. Could Zana have been a descendent of the Denisovans?
It's possible that archaic populations found niches in remote forested and mountainous areas of Europe, such as the Caucuses, Urals and Altai ranges and they may have lived on in these isolated areas until recent times. The Medieval accounts of "hairy men" and the "wood woo" may actually be anecdotal sightings of archaic hominids.Source

1 comment:

Aldstadt Harry said...

Interesting article. I recently had my DNA tested by the Genographic Project and the results came back with a small percentage of Neanderthal (1.7%) but an unexpected large percentage of Denisovan (3.5%). I have blond hair, light skin, blue eyes and would be classified as Northern European (45%).