Saturday, January 26, 2013

When was the split?


Genetic data suggest that ancestral East Asians diverged from ancestral Europeans long after the African/non-African split (source). This timeline, however, seems to be challenged by archaic DNA that is reputed to be 40,000 years old.

 
When did the ancestors of Europeans and East Asians part company? In my opinion, the divergence must have happened long after the time (c. 50,000 BP) when modern humans began to spread out of Africa. It probably occurred near the onset of the last ice age (25,000 – 10,000 BP), when advancing ice sheets and glacial lakes restricted gene flow between the western and eastern ends of Eurasia (Rogers, 1986).

This timeline is supported by several pieces of evidence:

1. Human skin began to lighten some 30,000 years ago in a population that was ancestral to both Europeans and East Asians (Beleza et al., 2012). A second phase of skin lightening, which affected only Europeans, occurred between 19,000 and 13,000 years ago. Proto-Eurasians must have therefore begun to diverge into two groups somewhere between 30,000 BP and 19,000 BP.

2. A Y-chromosome study suggests that all North Eurasian peoples descend from a common ancestral population dated to about 15,000 BP (Stepanov & Puzyrev, 2000; see also Armour et al., 1996; Santos et al., 1999; Zerjal et al., 1997).

3. The language families of northern Eurasia, particularly Uralic and Yukaghir and more generally Uralic-Yukaghir, Eskimo-Aleut, Chukotko-Kamchatkan and Altaic, share deep structural affinities that point to a common origin and not simply to word borrowing (Cavalli-Sforza, 1994, pp. 97-99; Fortescue, 1998; Rogers, 1986).

4. Archeological evidence (characteristic lithic technology, grave goods with red ocher, and sites with small shallow basins) shows the presence of a common cultural tradition throughout Europe and Siberia 20,000 to 15,000 years ago (Goebel, 1999; Haynes, 1980; Haynes, 1982).

5. Dental and cranial remains from Mal’ta (23,000-20,000 BP) in southern Siberia indicate strong affinities with Upper Paleolithic Europeans (Alexeyev & Gokhman, 1994; Goebel, 1999).

Back to the drawing board?

Nonetheless, this timeline now seems disproved by a recent study of archaic DNA:

We have extracted DNA from a 40,000-y-old anatomically modern human from Tianyuan Cave outside Beijing, China. […] The nuclear DNA sequences determined from this early modern human reveal that the Tianyuan individual derived from a population that was ancestral to many present-day Asians and Native Americans but postdated the divergence of Asians from Europeans. (Fu et al., 2013)

So ancestral Europeans and East Asians had already begun to diverge from each other by 40,000 BP. Considering that modern humans entered the Middle East around 46-47,000 BP, the time of divergence must have been close to the initial split between Africans and non-Africans (Schwarcz et al., 1979). Yet the genetic data argue otherwise.

When a new finding seems inconsistent with other data, one should take a second look. Do those human remains from Tianyuan Cave really date back to 40,000 years ago? Actually, they were initially dated to 25,000 BP, by means of uranium series dating of deer teeth from the same cave layer (Tong et al., 2004). Because this dating method is considered problematic when applied to organic remains, radiocarbon dating was later used to get a firmer date, which turned out to be 39,000 – 42,000 BP (Shang et al., 2007).

The two dating methods differed by 15,000 years. That’s a big discrepancy, and it may be why Shang et al. (2007) repeated their radiocarbon dating on several organic remains from the same layer. Such an approach, however, doesn’t rule out the possibility of a shared source of error, either in the remains themselves or in the testing laboratory.

There are two other reasons for doubting the estimate of 40,000 BP:

Associated faunal remains

The modern human remains from layer III were associated with the remains of other fauna. In general, the faunal assemblage indicates a significantly colder climate than the one that now prevails around Beijing. On the one hand, layer III had remains of the Siberian musk deer (Moschus moschiferus), which now lives farther north in the taiga of southern Siberia and northern Manchuria. On the other hand, layer III had no remains of warm climate species, i.e., the rhesus macaque (Macaca mulatta) and the masked palm civet (Paguma larvata), even though these species were present in the uppermost Holocene layer (Shang et al., 2007). The faunal evidence is thus consistent with the colder climate that existed when the last ice age began 25,000 years ago. It is not consistent with the warmer climate that prevailed 40,000 years ago in southern Siberia and northern China during the Malokheta Interstade of the Karga Interglacial (33,000 - 43,000 BP). At that time, average annual temperatures were as much as 2-3° C warmer than they are today (Goebel, 2004).

An outlier among finds of early East Asians

With a dating of 40,000 BP, these remains are much older than all other known finds that might be ancestral to present-day East Asians. The oldest rivals to Tianyuan Cave are Yamashita-cho, Okinawa (≈32,000 BP), Zhoukoudian Upper Cave, China (24,000 – 29,000 BP), Pinza-Abu, Okinawa ( ≈26,000 BP), and Minatogawa, Okinawa (≈18,000 BP) (Shang et al., 2007).

Conclusion

Archaic DNA promises to revolutionize our understanding of human origins. Unfortunately, it may also confer an aura of false certainty on new findings, thereby discouraging the healthy skepticism that makes good science possible. The Tianyuan Cave remains are undoubtedly those of an early East Asian and thus promise to shed much light on the beginnings of this branch of humanity. There are, however, reasons for doubting the date of 40,000 BP, and such doubts will probably become more insistent as we retrieve archaic DNA from other East Asian remains.

References

Alexeyev, V.P., & I.I. Gokhman. (1994). Skeletal remains of infants from a burial on the Mal'ta Upper Paleolithic site, Homo, 45, 119‑126.

Armour, J.A.L., T. Anttinen, C.A. May, E.E. Vega, A. Sajantila, J.R. Kidd, K.K. Kidd, J. Bertranpetit, S. Paabo, A.J. & Jeffreys. (1996). Minisatellite diversity supports a recent African origin for modern humans, Nature Genetics, 13, 154‑160.

Beleza, S., A. Múrias dos Santos, B. McEvoy, I. Alves, C. Martinho, E. Cameron, M.D. Shriver, E.J. Parra, & J. Rocha. (2012). The timing of pigmentation lightening in Europeans, Molecular Biology and Evolution, 20, online

Cavalli-Sforza, L.L., P. Menozzi, & A. Piazza. (1994). The History and Geography of Human Genes, Princeton: Princeton University Press.

Fortescue, M.D. (1998). Language Relations across Bering Strait. Reappraising the Archaeological and Linguistic Evidence, Cassell: London.

Fu, Q., M. Meyer, X. Gao, U. Stenzel, H. A. Burbano, J. Kelso, & S. Pääbo. (2013). DNA analysis of an early modern human from Tianyuan Cave, China, Proceedings of the National Academy of Sciences U.S.A., published ahead of print January 22, 2013, doi:10.1073/pnas.1221359110
http://intl.pnas.org/content/early/2013/01/17/1221359110.abstract

Goebel, T. (2004) “The early Upper Paleolithic of Siberia” (pp. 162-195) in S.L. Kuhn, K.W. Kerry (eds). The Early Upper Paleolithic beyond Western Europe, University of California Press.

Goebel, T. (1999). Pleistocene human colonization of Siberia and peopling of the Americas: An ecological approach, Evolutionary Anthropology, 8, 208‑227.

Haynes, C.V. (1982). Were Clovis progenitors in Beringia? In D.M. Hopkins (ed). Paleoecology of Beringia, New York: Academic Press, pp. 383‑398.

Haynes, C.V. (1980). The Clovis culture, Canadian Journal of Anthropology, 1, 115‑121.

Rogers, R.A. (1986). Language, human subspeciation, and Ice Age barriers in Northern Siberia, Canadian Journal of Anthropology, 5, 11‑22. 

Santos, F.R., A. Pandya, C. Tyler‑Smith, S.D.J. Pena, M. Schanfield, W.R. Leonard, L. Osipova, M.H. Crawford, & R.J. Mitchell. (1999). The Central Siberian origin for Native American Y chromosomes, American Journal of Human Genetics, 64, 619‑628.

Schwarcz, H.P., B. Blackwell, P. Goldberg, & A.E. Marks. (1979). Uranium series dating of travertine from archaeological sites, Nahal Zin, Israel, Nature, 277, 558-560.

Shang, H., H. Tong, S. Zhang, F. Chen, & E. Trinkaus. (2007). An early modern human from Tianyuan Cave, Zhoukoudian, China, Proceedings of the National Academy of Sciences U.S.A., 104, 6573-6578.
http://www.pnas.org/content/104/16/6573.full

Stepanov, V.A., & V.P. Puzyrev. (2000). Evolution of Y‑chromosome haplotypes in populations of North Eurasia, American Journal of Human Genetics, 67, 220.

Tong, H., H. Shang, S. Zhang, & F. Chen. (2004). A preliminary report on the newly found Tianyuan Cave, a Late Pleistocene human fossil site near Zhoukoudian, Chinese Science Bulletin, 49, 853-857.
http://link.springer.com/article/10.1007%2FBF02889760?LI=true

Zerjal, T., B. Dashnyam, A. Pandya, M. Kayser, L. Roewer, F.R. Santos, W. Scheifenhövel, N. Fretwell, M.A. Jobling, S. Harihara, K. Shimizu, D. Semjidmaa, A. Sajantila, P. Salo, M.H. Crawford, E.K. Ginter, O.V. Evgrafov, & C. Tyler‑Smith. (1997). Genetic relationships of Asians and Northern Europeans, revealed by Y‑chromosomal DNA analysis, American Journal of Human Genetics, 60, 1174‑1183.

 

16 comments:

Sean said...

Tianyuan man "did not carry a larger proportion of Neanderthal or Denisovan DNA than present-day people in the region." Here. 40,000 years old? I doubt it.

gcochran said...

That AMS C-14 date is solid.

Sean said...

Stable isotope dietary analysis of the Tianyuan 1 early modern human' says it lived on fish for a substantial part of the year; which could only be due to scarcity of animals to hunt, yet the area was swarming with game during the Malokheta Interstade.

If there were enough Tianyuan man like hunters to deplete the game 40,000 years ago; why is Tianyuan man the only example to be found?

Anonymous said...

Maybe they preferred fish or were better fishermen or fish were easier to catch than the land game.

Sean said...

It's the earliest date for freshwater food exploitation in Eurasia, and to show up in the analysis it must have been year round. All very odd.

Chinese scientists are prone to claiming that the there is continuity of humans in China as far back as you can go.

Anonymous said...

What about saltwater fishing? Was there saltwater fishing before then?

Ben10 said...

"Chinese scientists are prone to claiming that the there is continuity of humans in China as far back as you can go"

Yes, and it's pretty much the opposite of the funded occidental researcher, who is lobbied to find that 'europeans' never existed and were initially transposed africans.
My bet is that, deep inside, and despite the appearences given for the occidental medias, chinese evolutionists are not darwinian by essence. Darwinism as a causal force is completely antithetic of confusianism, boudhism or even chamanism.

Sean said...

Western scientists' involvement is no guarantee of objectivity. Note the claim (once widely accepted) that there was use of fire by Peking man for lighting, cooking, and heating at Zhoukoudian 400,000 years ago.

Anonymous said...

I believe Peking Man is now believed to be from 750,000 years ago.

Ben10 said...

This is basically as old as Cro magnon.
So, 'differentiated from europeans'? but what europeans?

Hypothesis number 1:
African Hunters looking more or less like Buhmen (with asian traits) reach Eurasia and loose all their afro-asian features to become european-like Cro Magnons. Once in Asia these cro-magnons reacquire asian features and loose their european features.

Or hypothesis number 2:
African Hunters looking more or less like Buhmen reach Eurasia but DO NOT loose their afro-asian features immediately, so Cro Magnons must have looked partly like robust afro-asian or Bushmen. 40 000 years ago, some of them move in Asia where these loose some African features but retain the bushmen-asian features, while those who stayed in Europe loose both their African Bushman and asian features.

In hypothesis 2 nothing is lost then reacquired, and this is much more economic than hyp. 1) so the so-called 'europeans Cro-Magnons' must have looked like robust Bushmen more than Europeans.

I retouched a picture of a San Buhsman from Africa to show how these "Africans' actually look more asian or amerindian than African. I choose a Thai man by comparison and a reconstruction of a 11500 years old south amerindian from Wikipedia.

[IMG]http://i48.tinypic.com/16gyeyr.jpg[/IMG]

Ben10 said...

The other one (Bushman to amerindian) is
http://i49.tinypic.com/os5xtg.jpg

just copy paste the link, too bad the forum doesn't take html lins.

Sean said...

Tianyuan is 10,000 years before the next earliest date for freshwater fishing (hooks found in E.Europe which may have actually been for hunting water-birds.)

Fish is nice for a change, but I don't think it would be a staple food by choice . Anyway, men don't hunt just for food; they do it by way of demonstrating prowess.

Anonymous said...

"Stable isotope dietary analysis of the Tianyuan 1 early modern human' says it lived on fish for a substantial part of the year; which could only be due to scarcity of animals to hunt, yet the area was swarming with game during the Malokheta Interstade."

If you look at it from the point of view of food-getting then there are three options
- gathering
- hunting
- fishing

Early humans who developed fishing might have been able to expand much faster than the others as long as they stuck to coasts and rivers.

In terms of out of africa that gives two dramatically different and divergent routes: a southern coastal one and an atlantic one - with possible later hunter and/or gatherer expansions as they caught up.

I do wonder about those Bushmen eyefolds.

Anonymous said...

It's a completely different time period but coincidentally

http://forwhattheywereweare.blogspot.co.uk/2013/01/whale-remains-reinforce-notion-of.html

whale-hunting along the atlantic coast could be a later example of sea-based adaptation and subsequent expansion.

Ben10 said...

...my point was that asians did not differentiate from europeans, since there were no true europeans at that time. They differentiated from asian-like africans who lived in Europe.

Also, what is PNG in the figure? Anyway, i scooped the article quickly but notice that the authors clearly state in Table4 that Neanderthals are closer to europeans (non africans) than Africans. So reciproquely, Europeans are closer to Neanderthals than Africans.
Since we consider Neanderthals a separate sub species of homo sapiens, that makes Africans an even more separate sub species.

genetiker said...

This is what really happened.