Friday, January 09, 2009

First Americans ... new DNA hypotheses

Were the Americas populated through an ice-free corridor that opened up east of the Rocky Mountains, or did people come down the Pacific Coast, headland to headland, possibly using boats? Well, both, says a new scientific paper that claims to be even more precise in its DNA analyses.

The ice-free corridor explanation ruled for most of a century. But evidence continued to accumulate that people were south of the ice in the Americas before the glaciation could have retreated enough to provide any kind of corridor. Archaeologist Knut Fladmark of Simon Fraser University pioneered the theory of a coastal migration. Rising sea levels 10,000 years ago put all the archeological sites that might have tested his theory at least 100 metres below the modern low water mark, but Fladmark set out the argument and awaited the development of submarine archaeology -- which has indeed provided some teasing hints of just the evidence he was predicting. And, despite a complete lack of evidence for boats in northern waters so long ago, it makes a kind of sense that a seagoing or shore-going people would have moved south into South America more rapidly than peoples adapted to hunting on the North American interior. So for all the lack of definitive evidence, the coastal migration theory gained a lot of adherents in the last quarter-century or so.

From their press quotations, the Italian DNA scientists who are bringing forth the new data and the new interpretation seem only roughly familiar with all those decades of arguments. But they seem to be up for a compromise: a coastal migration took people with one set of DNA haplotypes right down the west coast and into South America. An inland migration through the gap between the glaciers that did eventually open up brought other people, with a slightly different DNA set, into the interior of North America, where they stayed.

Since both groups came from Asia, and not far apart in time or space, it's not clear how much of a difference there is here. I recall archaeologist Lewis Binford dismissing the whole controversy with a rasping "Who care which river valley they came down? That doesn't implicate any new knowledge." But splitting DNA haplogroups ever more finely is what the DNA science does superbly these days. Look for more of it, maybe even working out dates and sequences.
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