Thursday, March 12, 2009

Redating gives older age to Chinese Homo erectus

Paleoanthropology news so big, it makes the cover of the current Nature (left), albeit with a lame headline that says, "Peking Man was Cool." I know, lame, right? Like the editor was trying to be 'hip' and reach a new generation of nerds. Although 'cool' has been used since like the 1950s. And I peruse Nature, so it's not nerdy.

Anyway, yes, researchers working at the Zhoukoudian (aka Chokoutien, etc.) cave site in China have redated the Homo erectus-bearing layers. As is the problem with the South African cave sites from which we get some great Australopithecus fossils (and "Paranthropus," if you're so inclined), cave sites are difficult to date radiometrically, with absolute dates based on the decay of radioactive materials. Before now, Zhoukoudian had been dated to about 500-250 ka (thousand years ago). Such a date is roughly contemporaneous with some "archaic Homo sapiens" (whatever that really means) fossils, which are generally thought to be intermediate in morphology between Homo erectus and modern people such as you or I. Could this indicate the coexistence of Homo erectus and more 'modern' people?

Well, the site has now been dated to about 770 ka, plus or minus 80ka (Shen et al. 2009). This means that the hominin occupations at the site start at nearly 800 ka, and end around 400 ka. Does this older date mean that now the overall picture of human evolution is clear? Of course not. But, it does fit the same kind of pattern we see elsewhere. The new dates show that, like in other areas, older more classically erectus-like hominins predate more intermediate "archaic" forms of humans. Moreover, it's now certain that these fossils don't (at least not the older ones) overlap in time with younger, "archaic" humans, such as that from Jinniushan.

So I guess that's the main point, that the earlier dates of Zhoukoudian emphasize the fact that evolutionary trends in Asian middle Pleistocene hominins are the same as those throughout the world. If you really think that all these ancient regions represent separate species or distinct lineages, I suppose you could argue that this pattern of similarity means parallel evolution. A much more sensible interpretation, in my opinion, is that these populations were connected, even if only sporadically, by gene flow.

1 comment:

jamielc said...

These new dates were presented at the Paleos last year and didn't seem to catch as much attention as I expected, so I'm glad to see this now, and hooray for paleoanthro stuff getting the front page of Nature!