Wednesday, July 6, 2011

Altai Once Warmer

Denisovia, a cave in the Altai region of Russia is famous as the source of non-Neanderthal, non-modern human bones that left genetic traces in Melanesians, and much later, as a cradle of major language families like those that include Mongolian, Turkish, Manchurian, and perhaps Korean and ancient Japanese.

According to John Hawks, who is there right now and tweeting from his Kindle 3G, it is also a rich source of new paleoclimatic data. The region appears to have had hominin occupation from about 250,000 years ago, and to have been much warmer than modern Siberia for most of the period prior to the last glacial maximum around 20,000 years ago.

This is quite surprising, since the conventional account is that Siberia was mostly uninhabited until relatively late after the Out of Africa period and made only a minority contribution to the modern populations of the Americas and East Asia, which show strong genetic indications of Southern Coastal Route origins. Indeed, some genetic haplotypes appear to have made their way along the Eurasian coast to North Asia and back to Northern Europe again via a basically circumpolar route. Megafauna extinction also seems to come fairly late to Siberia.

UPDATED in response to comment (since the comment function seems to be cranky this morning):

Until the Denisovian site was discovered, there was no evidence of Neanderthals or anything similar much further east than the Caucusas and Persia.

I'm not aware of any Homo Erectus sites in mainland Asia dated later than 400 kya to the present, with the possible exception of one from about 100 kya that might actually be a very early AMH or hybrid individual. Their presence has been inferred from the presence 1.8 mya to 400 kya and the absence of anything else we knew of until AMHs arrived, but there was very little evidence of pre-AMH hominins in mainland Asia for any of this time period from ca. 400 kya to 50 kya.

There was some thin evidence of AMHs in Siberia pre-LGM, but IIRC this isn't reliably earlier than about 30 kya in Eastern Siberia when a megafauna extinction makes their presence known. As I understand it, the conventional wisdom is that most of Siberia, like Northern Europe, was abandoned in favor of refugia during the most recent major ice age, and then repopulated from those refugia. (With entry of proto-Americans into Bergingia not entirely obviously just before or just after the LGM.)

The Denisovian find, of course, changes that picture immensely, both by providing evidence of continous occupation from the early Paleolithic to the early Upper Paleolithic and by providing DNA whose legacy that has turned up in Melanesia and to a lesser degree in populations admixed with them. Homo Florensis also provides archaic hominin evidence in the Middle to Upper Paleolithic era in Asia (if not mainland Asia) again corroborating the inference that archaic hominins were probably not absent for a 350,000 year period in Asia.

The sense that I get from John Hawks account is that Denisovia's paleoclimate evidence is also supporting an Altai that was much warmer than it is today in the time period from ca. 250 kya to 30 kya (i.e. pre-ice age). Naiively, we would have expected temperatures pre-ice age to be similar to what they are now, post-ice age. I'm not aware of any obvious mechanism that could make the Altai that warm from 250 kya to 30 kya, but nature didn't ask me what it should do back then and we'll have to figure it out.

1 comment:

Maju said...

Altai was inhabited all the time. Siberia in general was dry cold, without ice or snow in most of its extension in the Ice Age. It was also full of lakes, blocked by the northernly Ice Sheet, as you can see here (scroll down to bottom of page) but it was not covered in ice/snow because the climate was too dry for that.

"... the conventional account is that Siberia was mostly uninhabited until relatively late after the Out of Africa period"...

Not really, what happened is that it was inhabited by Neanderthals and those pesky "Denisovan" hybrids (?)

That was also the case of Europe for example. Actually Altai and Europe (all West and Central Eurasia in fact make a single region for this purpose) were colonized in about the same period 48-40 Ka ago and by related peoples who used the same kind of "Aurignacoid" technology and left the same kind of genetic legacy.