Message 1 of 209 (597615) 12-22-2010 6:25 PM

A previously unknown kind of human—the Denisovans—likely roamed Asia for thousands of years, probably interbreeding occasionally with humans like you and me, according to a new genetic study.

In fact, living Pacific islanders in Papua New Guinea may be distant descendants of these prehistoric pairings, according to new analysis of DNA from a girl's 40,000-year-old pinkie bone, found in Siberian Russia's Denisova cave.

This "new twist" in human evolution adds substantial new evidence that different types of humans—so-called modern humans and Neanderthals, modern humans and Denisovans, and perhaps even Denisovans and Neanderthals—mated and bore offspring, experts say.

"We don't think the Denisovans went to Papua New Guinea," located at the northwestern edge of the Pacific region called Melanesia, explained study co-author Bence Viola, an anthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

"We think the Denisovan population inhabited most of eastern Eurasia in the same way that Neanderthals inhabited most of western Eurasia," Viola said. "Our idea is that the ancestors of Melanesians met the Denisovans in Southeast Asia and interbred, and the ancestors of Melanesians then moved on to Papua New Guinea."

(See "Interspecies Sex: Evolution's Hidden Secret?")

Interbreeding Common Among Various Types of Humans?

Taken together with a May DNA study that found Neanderthals also interbred with modern human ancestors, the Denisovan finding suggests there was much more interbreeding among different human types than previously thought, Stanford University geneticist Brenna Henn said.

"In the actual archaeological record, people have been talking about this for a long time ... But before six months ago, there was no genetic evidence for any admixture between archaic humans and modern humans," said Henn, who co-authored an article accompanying the study in tomorrow's issue of the journal Nature.

"Then these two papers come out, and I won't say they've turned the field on its head, but they certainly support a view that has not been well recognized for years" by geneticists, said Henn, who wasn't part of the study.

Brian Richmond, a paleoanthropologist at George Washington University, said he expects the new study to spark much interest and excitement.

"Nothing is more intriguing than learning new twists about our origins," said Richmond, who also didn't participate in the Denisovan-genetics research. "And this is another new twist."

Fossil Finger Points to New Human Type

The centerpiece of the DNA study is a Denisovan fossil finger bone discovered in 2008. The fossil is thought to be from a young girl—dubbed X-woman—who was 5 and 7 years old when she died.

For a previous Nature study, released in March 2010, the team had collected and sequenced mitochondrial DNA, or mtDNA, from X-woman's finger. But mtDNA—inherited only from mothers—contains far less information about a person's genetic makeup than DNA found in the nucleus of a cell, or nuclear DNA (quick genetics overview).

In the new study the team reports successfully extracting and sequencing so-called nuclear DNA from the bone.

Then, using DNA-comparison techniques, the scientists were able to determine that Denisovans were distinct from both modern humans and Neanderthals, yet closely related to the latter.

The team estimates Denisovans split from the parent group of Neanderthals about 350,000 years ago.

Message 2 of 209 (597620) 12-22-2010 6:37 PM

Reply to: Message 1 by ramoss 12-22-2010 6:25 PM

This finding, if confirmed, would add support to the multiregional theory.

Message 3 of 209 (597631) 12-22-2010 7:46 PM

Reply to: Message 2 by Coyote 12-22-2010 6:37 PM

To my untrained mental eye, it looks as though you could interpret the findings as evidence that H. sapiens migrating from Africa pushed Neanderthals and their Denisovan cousins to "the ends of the earth".

I thought the multiregional explanation was the descent of modern Europeans from Neanderthals--perhaps I'm badly outdated, or simply wrong in that understanding?

Real things always push back.
-William James

Message 4 of 209 (597641) 12-22-2010 8:55 PM

Reply to: Message 3 by Omnivorous 12-22-2010 7:46 PM

The multiregional hypothesis seems to be incorrect for the west, Africa and Europe, but I wonder if these findings may not support it for eastern Asia. I have always wondered about some line traits from Asian erectus that seem to persist into modern Asian groups. The finding that there was an additional, previously unknown species in east Asia and that it has some living descendants just adds to the problem--and the question of just how much interbreeding was going on that has not previously been recognized.

From the article:

On the basis of the new findings, the scientists propose that the ancestors of Neanderthals and Denisovans emerged from Africa half a million years ago. The Neanderthals spread westward, settling in the Near East and Europe. The Denisovans headed east. Some 50,000 years ago, they interbred with humans expanding from Africa along the coast of South Asia, bequeathing some of their DNA to them. ...

The Massachusetts scientists concluded that the finger bone belonged to a hominin branch that split from the ancestors of Neanderthals roughly 400,000 years ago. Dr. Paabo and his colleagues have named this lineage the Denisovans. ...

Next, the researchers looked for evidence of interbreeding. Nick Patterson, a Broad Institute geneticist, compared the Denisovan genome to the complete genomes of five people, from South Africa, Nigeria, China, France and Papua New Guinea. To his astonishment, a sizable chunk of the Denisova genome resembled parts of the New Guinea DNA.

“The correct reaction when you get a surprising result is, ‘What am I doing wrong?’ ” said Dr. Patterson. To see if the result was an error, he and his colleagues sequenced the genomes of seven more people, including another individual from New Guinea and one from the neighboring island of Bougainville. But even in the new analysis, the Denisovan DNA still turned up in the New Guinea and Bougainville genomes.

Link

Given the DNA showing up in New Guinea and Bougainville, there does seem to have been interbreeding. Now the question is among whom, and how much?

But given the persistence of this new DNA in Asia from 400,000 or 500,000 years ago to modern humans, there seems to be some support for the multiregion hypothesis in eastern or southeastern Asia.

Add:

From another article:

Paabo says the DNA they already have does indicate that this Siberian stranger, along with humans and Neanderthals, evolved from some common ancestor that lived in Africa about a million years ago. "Whoever carried this mitochondrial genome out of Africa about a million years ago is some new creature that has not been on our radar screens so far," he says.

Scientists know generally when this new hominid — as human ancestors are known — appeared on the scene by comparing the number of mutations in the DNA of humans, Neanderthals and the X-woman. Mutations occur in a population at a certain rate that can indicate how long they've evolved separately from a common ancestor.

Though Paabo can't say if this was an unknown species on the human line, he can say the X-woman's ancestors probably migrated from Africa a million years ago, well before modern humans evolved.

http://www.npr.org/tablet/#story/?storyId=125129322

Edited by Coyote, : Added information

Edited by Coyote, : Add link

Message 5 of 209 (597654) 12-22-2010 11:10 PM

Reply to: Message 4 by Coyote 12-22-2010 8:55 PM

Do you suppose migrations of H. sapiens into those areas were more likely to result in interbreeding rather than displacement of the older population because the earlier migrations were too well established to just push out of the way? I know the Neanderthal were physically robust, but I've somehow gathered the impression that their population sizes were not.

I read through David Johanson's summary at Action Bioscience. It is a popular account, somewhat dated, I suppose, since it's copyrighted 2001, but it has been useful to me in understanding the history.

He notes:

quote:

---

Proponents of the Multiregional Model, such as Milford Wolpoff, cite evidence in Asia of regional continuity. They see an evolutionary link between ancient Homo erectus in Java right through to Australian aborigines. A possible problem with this view is that recent dating of late surviving Homo erectus in Indonesia suggests that they survived here until 50,000 years ago, which is potentially when fully modern humans may have arrived in the region from Africa.

China may contain the best evidence for supporting the Multiregional Model. Here there are discoveries of a couple of skulls dated to roughly 100,000 years ago that seem to possess a mixture of classic Homo erectus and Homo sapiens traits. Better geological dating and more complete specimens are needed to more fully assess this possibility.

---

Is the arrival of modern humans there at 50,000 y.a. really a problem for multiregional advocates? Their hypothesis explicitly describes interbreeding/gene flow, right?

Have those Chinese skulls (or subsequent finds) panned out?

Real things always push back.
-William James

Message 6 of 209 (597655) 12-22-2010 11:45 PM

Reply to: Message 5 by Omnivorous 12-22-2010 11:10 PM

My bet though is that there was some continuity in Asia, and it most likely took the form of interbreeding.

Modern humans certainly took over pretty well when they arrived, but I think they swamped out some of the earlier groups through interbreeding, rather than elimination and replacement.

This most recent DNA evidence seems to suggest that.

But I'd like to see it confirmed with a couple of additional sequences before I bet the rent money on it.

Message 7 of 209 (597656) 12-23-2010 12:32 AM

Reply to: Message 6 by Coyote 12-22-2010 11:45 PM

I felt vindicated when more recent DNA studies contradicted the early mitochondrial results and suggested some interbreeding between modern and Neanderthal populations.

I always found it difficult to believe that every H. sapiens male passed up every opportunity to mate with a Neanderthal, even if they were short, strong and chinless.

I mean, I've been in Asian bars at closing time...

Real things always push back.
-William James

Message 8 of 209 (597663) 12-23-2010 6:08 AM

Reply to: Message 2 by Coyote 12-22-2010 6:37 PM

It seems to me that this is closer to a refinement of the Out-Of-Africa hypothesis than support for the multiregional hypothesis, we're still looking at a single main H. sapeins that emerged from Africa, just now with some slight admixture from other Homo species (or subspecies?).

The multiregional hypothesis held that there were distinct mainlines in different regions; this remains clearly wrong.

Message 9 of 209 (597686) 12-23-2010 10:54 AM

Siberian Fossils Were Neanderthals’ Eastern Cousins, DNA Reveals

--Percy

Message 10 of 209 (597714) 12-23-2010 4:21 PM

Reply to: Message 8 by Mr Jack 12-23-2010 6:08 AM

No; it didn't. The key to MH is that it supposes the regional populations remained genetically linked to one another and so evolved as something of a single 'world population'. If so, we should find some regional genetic links between past homo varieties and modern h. sapiens native to those same regions.

That is why this finding adds support to MH, since it shows that past and present homo varieties were not only capable of breeding, but did breed. The one-off African origin (of h. sapiens) proposed by OOA is simply not adequate for explaining this continuation of regional variations into present human lines—at least some aspects of modern humanity must have evolved outside of Africa prior to 50-60 kya.

Jon

Edited by Jon, : Clarifications

Message 11 of 209 (597786) 12-24-2010 4:38 AM

Reply to: Message 10 by Jon 12-23-2010 4:21 PM

see this picture

Yes, but we're talking less than 10% of the genome. We're still talking about a species that evolves in Africa spreading through the world, and replacing existing populations. That there was a small degree of gene flow from those populations alters that details of that picture but it doesn't change the overall narrative.

According to this research, H. sapiens evolved in Africa and spread to melanasia. Once there there was a small degree of interbreeding. That still Out of Africa.

Message 12 of 209 (597826) 12-24-2010 12:08 PM

Reply to: Message 11 by Mr Jack 12-24-2010 4:38 AM

The replacement model is simply not accurate. This finding supports the notion that h. sapiens mixed with the earlier populations rather than merely replaced them. This is something predicted by MH; OOA proponents, on the other hand, have not been able to make these predictions, and have resorted to constant alterations of their model to explain new and contradictory evidence—in similar fashion to the epicycles of geocentrism.

Jon

Edited by Jon, : clarity

Message 13 of 209 (597932) 12-25-2010 6:11 PM

Reply to: Message 12 by Jon 12-24-2010 12:08 PM

I want to make sure I understand what formulation of the multiregional hypothesis you embrace and consider evidenced by this new data.

Here's a summary of the debate by David Johanson:

quote:

---

The Multiregional Continuity Model contends that after Homo erectus left Africa and dispersed into other portions of the Old World, regional populations slowly evolved into modern humans. This model contains the following components:

* some level of gene flow between geographically separated populations prevented speciation after the dispersal;

* all living humans derive from the species Homo erectus that left Africa nearly two million-years-ago;

* natural selection in regional populations, ever since their original dispersal, is responsible for the regional variants (sometimes called races) we see today;

* the emergence of Homo sapiens was not restricted to any one area, but was a phenomenon that occurred throughout the entire geographic range where humans lived.

--------------------------------------------

In contrast, the Out of Africa Model asserts that modern humans evolved relatively recently in Africa, migrated into Eurasia and replaced all populations which had descended from Homo erectus.

Critical to this model are the following tenets:

* homo sapiens arose in Africa and migrated to other parts of the world to replace other hominid species, including homo erectus;

* after Homo erectus migrated out of Africa the different populations became reproductively isolated, evolving independently, and in some cases like the Neanderthals, into separate species;

* Homo sapiens arose in one place, probably Africa (geographically this includes the Middle East);

* Homo sapiens ultimately migrated out of Africa and replaced all other human populations, without interbreeding;

* modern human variation is a relatively recent phenomenon.

--------------------------------------------

The multiregional view posits that genes from all human populations of the Old World flowed between different regions and by mixing together, contributed to what we see today as fully modern humans.

The replacement hypothesis suggests that the genes in fully modern humans all came out of Africa. As these peoples migrated they replaced all other human populations with little or no interbreeding.

---

Do you agree with his description of the competing hypotheses?

Real things always push back.
-William James

Message 14 of 209 (598078) 12-27-2010 8:19 PM

Reply to: Message 13 by Omnivorous 12-25-2010 6:11 PM

Jon

Message 15 of 209 (598112) 12-28-2010 6:42 AM

Reply to: Message 13 by Omnivorous 12-25-2010 6:11 PM

Please note I am quoting Johanson through Omnivorius' post.

The Multiregional Hypothesis:

Seems reasonable, particularly considering recent findings.

Seems unreasonable, particularly considering recent findings.

As Damon Wayans when playing the clown from In Living Color would say "homie don't think so" right before he clubbed someone over the head. Recent DNA evidence indicates all are essentially modern Homo Sapiens, with a slight bit of spice from Neanderthals and/or Denisovans.

Doubtful, smells like appeal to magic.

Now for the converse:

Homo Erectus appears to be more a cousin than a direct ancestor according to the most modern interpretations of physical anthropology, in accordance with actual physical measurements of the fossils.

Guess we will have to wait for some shred of DNA from Homo Erectus to make this one work out. In the meantime it appears both Homo Sapiens and Neanderthals evolved from Homo Rhodesiensis, rather than Homo Erectus.

This hypothesis would, of course, fit in with the evolution of any other critter, be it observed or evidenced by the scanty fossil record.

Oops, the most recent DNA evidence indicates their was some slight inbreeding between modern Homo Sapiens, Neanderthals and the more recently speculated Denisovans.

Almost entirely, except for that lil' bit of DNA evidence.

I think the 'Out of Africa' hypothesis is mostly correct except for that smidgen of DNA from our distant cousins, none of which has been shown to be from erectus. One reason I see slight interbreeding is due to that old saying from New Mexico Tech "Socorro, where women are men and sheep are restless."

Reality is always more complex than a slogan.

This rudderless world is not shaped by vague metaphysical forces. It is not God who kills the children. Not fate that butchers them or destiny that feeds them to the dogs. It’s us. Only us. - the character Rorschach in Watchmen