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View Full Version : These ancient Chinese teeth could rewrite human history



PLogan
10-15-2015, 06:21 PM
https://www.washingtonpost.com/news/speaking-of-science/wp/2015/10/15/these-ancient-chinese-teeth-could-rewrite-human-history/

"A set of 47 human teeth found in China is giving scientists a lot to chew on. The teeth have been dated as at least 80,000 years old -- perhaps even older. The problem with that is that most researchers believe humans only left Africa for the first time around 60,000 years ago. And even then, they were thought to trek to Europe first, not Asia."

Piquerobi
10-15-2015, 11:21 PM
Interesting!

Megalophias
10-15-2015, 11:50 PM
Why would you want to talk about this, it's so much more interesting to speculate about which sub-sub-sub-clade of R1b was where in Europe a few thousand years ago. ;)

Several possibilities:
1) The date is wrong. Always possible, but this isn't the first such case, and everything looks pretty solid (not that I know anything about radioisotope dating). 14C puts the bones at minimum 43 000 years old.
2) Convergent evolution of some other hominin toward AMH morphology. Conceivable, but apparent these are very modern in their morphology.
3) An early wave Out of Africa which either went extinct or became very diluted. A recent paper argued that Australians and Papuans have ancestry from an earlier Out of Africa migration. If some of them were still hanging out in China and contributed minor ancestry to some later groups this might also explain the Australo-Melanesian ancestry that showed up in Amazonians. Since this is pre-Toba, they could have been wiped out or at least weakened by the eruption. On the other hand, the ash cloud blew northwest, so China didn't actually get hit that hard.
4) The main wave Out of Africa!

Number four would be the most interesting, of course. The biggest problem I see is with mtDNA L3. It doesn't seem like M and N were separated from African L3 for tens of thousands of years, yet there are multiple specifically African L3 branches which seem unlikely to have back-migrated from Eurasia en masse. A similar objection applies to Y haplogroup E, but much less strongly.

Some features of uniparental marker distribution would actually make sense if Toba blew a hole in the middle of them, and CDEF/CF/DE seem to coalesce around then, but it would require some improbably specific timing.

Kale
10-16-2015, 03:16 AM
You forgot option 2.5) Modern humans inheriting the 'modern' features of these teeth from an archaic species.
One could really jump the gun and say these teeth are Denisovan, Denisovan had edar mutation, which introgressed into Asians, like a few have postulated...but I think option 1 is probably most likely.

Tomenable
10-16-2015, 02:58 PM
The problem with that is that most researchers believe humans only left Africa for the first time around 60,000 years ago.

Anatomically modern humans were in Australia already 62,000 years ago - see LM3 individual:

"Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins":

http://www.pnas.org/content/98/2/537.full.pdf

LM3's mtDNA lineage diverged from the rest of humanity after Neanderthals, but before "Eve".

This might suggest that modern humans expanded out of Africa more than once, but mtDNA lineages of those early groups got extinct, and only matrilineal descendants of "Eve" survived (they left Africa as the last OOA wave, and were most successful). Alternatively, there could be just one OOA expansion which included both descendants of "Eve" and descendants of other women, but for some reason only lineages descended from Eve survived.

Is it possible to extract DNA from these teeth in China, and check what was their mtDNA haplogroup?

I suppose they could be "pre-Eve dead ends", just like Lake Mungo 3 individual from Australia.

Inigo Montoya
10-16-2015, 03:15 PM
You forgot option 2.5) Modern humans inheriting the 'modern' features of these teeth from an archaic species.
One could really jump the gun and say these teeth are Denisovan, Denisovan had edar mutation, which introgressed into Asians, like a few have postulated...but I think option 1 is probably most likely.
Don't we have a tooth from Denisova Cave?

Megalophias
10-16-2015, 04:24 PM
Yes, we have a tooth, and it doesn't look AMH at all.

(On the other hand we also know that Denisovans were genetically diverse and that the ones who interbred with us were probably quite divergent from the ones in Denisova Cave. Still very far-fetched, though.)

They couldn't even find enough collagen in the teeth to do a radiocarbon dating, so I really doubt there is any DNA left, unfortunately.

parasar
10-16-2015, 04:45 PM
You forgot option 2.5) Modern humans inheriting the 'modern' features of these teeth from an archaic species.
One could really jump the gun and say these teeth are Denisovan, Denisovan had edar mutation, which introgressed into Asians, like a few have postulated...but I think option 1 is probably most likely.

Denisovans had EDAR? Which paper was that reported in?
Since it appears that EDAR, which is now key in identifying East Asians, did not originate among East Asians I thought it was back migration from the Americas.

Edit: Ah! I see that EDAR in Denisovan is just speculation.

Megalophias
10-16-2015, 07:01 PM
Some Chinese archaics reportedly have shovel-shaped incisors, which is one of the effects of the derived form of EDAR. However, there are also other genes that contribute to shovelling. In any case EDAR has numerous effects on skin-related tissues: hair, teeth, sweat glands, breasts. The shaping of teeth is almost certainly a meaningless side effect of whatever it does that is actually selected for (no one knows what that is). I doubt that shovel-shaped incisors in archaics have anything to do with modern EDAR alleles, though it's always possible.

Most genes do a whole bunch of things, lactase also breaks down a certain plant poison, for instance.

Inigo Montoya
10-16-2015, 07:36 PM
Denisovans had EDAR? Which paper was that reported in?
Since it appears that EDAR, which is now key in identifying East Asians, did not originate among East Asians I thought it was back migration from the Americas.

What is the source for EDAR not originating in East Asians (other than derived allele in SHG, I assume, since you mention the Americas)?

parasar
10-16-2015, 09:48 PM
What is the source for EDAR not originating in East Asians (other than derived allele in SHG, I assume, since you mention the Americas)?

One is the Iain Mathieson paper. The Motala have 0 East Asian but have EDAR.

The other is my own thinking based on:
1. Single migration to the Americas
2. Early Americans were Otomid Sundadonts.

Megalophias
10-17-2015, 07:43 PM
One is the Iain Mathieson paper. The Motala have 0 East Asian but have EDAR.

The other is my own thinking based on:
1. Single migration to the Americas
2. Early Americans were Otomid Sundadonts.

But how does any of this point to America?

Motala lacking East Asians counts against Amerindian origin as well, since Amerindians, even Paleoamerican Kennewick Man, are majority East Asian. If anything it suggests some minor Asian branch which mixed into multiple populations. Or the original ancestry could simply have been diluted beyond recognition as it spread under selection.

If EDAR370A really is specifically associated with modern Amerindian over Paleoamerican morphology - and EDAR370A does not all by itself cause Sinodonty or rule out Sundadonty, as far as I know - then it must have spread through the New World *after* the original colonization. And there must have been gene flow between America and East Asia either way. So what favours a New World origin?

Inigo Montoya
10-17-2015, 08:35 PM
But how does any of this point to America?

Motala lacking East Asians counts against Amerindian origin as well, since Amerindians, even Paleoamerican Kennewick Man, are majority East Asian. If anything it suggests some minor Asian branch which mixed into multiple populations. Or the original ancestry could simply have been diluted beyond recognition as it spread under selection.

If EDAR370A really is specifically associated with modern Amerindian over Paleoamerican morphology - and EDAR370A does not all by itself cause Sinodonty or rule out Sundadonty, as far as I know - then it must have spread through the New World *after* the original colonization. And there must have been gene flow between America and East Asia either way. So what favours a New World origin?

I was about to ask something similar, just less well worded.
I simply don't understand how that reasoning is supposed to work.

Inigo Montoya
10-17-2015, 08:40 PM
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parasar
10-18-2015, 09:52 PM
But how does any of this point to America?

Motala lacking East Asians counts against Amerindian origin as well, since Amerindians, even Paleoamerican Kennewick Man, are majority East Asian. If anything it suggests some minor Asian branch which mixed into multiple populations. Or the original ancestry could simply have been diluted beyond recognition as it spread under selection.

If EDAR370A really is specifically associated with modern Amerindian over Paleoamerican morphology - and EDAR370A does not all by itself cause Sinodonty or rule out Sundadonty, as far as I know - then it must have spread through the New World *after* the original colonization. And there must have been gene flow between America and East Asia either way. So what favours a New World origin?

That is the reason I mentioned a single migration to the Americas (23kybp is supported by the Willerslev team with a subsequent diversification) and an origin of EDAR there.

If a single migration is not the case (as posited by the Reich team), even then an EDAR origin in the Americas (or the Beringian part) is possible.

I have asked this question before - Is Anzick-1 derived for EDAR?
How about Kennewick Man?

Megalophias
10-18-2015, 10:16 PM
That is the reason I mentioned a single migration to the Americas (23kybp is supported by the Willerslev team with a subsequent diversification) and an origin of EDAR there.
Ravaghan et al found that a single migration with gene flow continuing afterward was the best fit. It would have to be all one way to prevent EDAR370A arriving later.

Anyway, sure it's possible, though estimates of the age of the derived EDAR haplotype are all much older than the usual dates for colonization of the New World.


I have asked this question before - Is Anzick-1 derived for EDAR? How about Kennewick Man?
Me too, and have never found anything. I suppose there was probably no call for the allele, but it is part of an extended haplotype, so you'd think it could be imputed.

Saqqaq has the derived allele, but that is expected.

Inigo Montoya
10-19-2015, 09:28 AM
On a completely different note, the authors of the papers suggest that humans didn't expand into Europe until much later because of a "Neanderthal barrier". Implicit in this reasoning is that Denisovans didn't constitute such a barrier further East. It's a shame they didn't expand on why that is.

Megalophias
10-19-2015, 03:22 PM
On a completely different note, the authors of the papers suggest that humans didn't expand into Europe until much later because of a "Neanderthal barrier". Implicit in this reasoning is that Denisovans didn't constitute such a barrier further East. It's a shame they didn't expand on why that is.

I think the implication was that modern humans were tropically adapted, so could compete with archaic humans in India, southern China etc on an even footing, but were initially at a disadvantage against cold-adapted Neanderthals.