DUELING PAPERS ABOUT THE FIRST AMERICANS
Oh, goody. Dueling papers. Always a treat. And dueling papers in the same week in Science and Nature, an extra-special treat.
The topic a hot one, as befits dueling papers: Based on genetic studies in ancient and modern Native American populations, whence cometh the First Americans?
Moreover, the studies were carried out by two of the 800-pound gorillas of genetic populations studies: David Reich’s Harvard lab (in Nature) and the group led by Eske Willerslev, based at the University of Copenhagen (in Science).
In fact, although you wouldn’t know it from the media, which loves a fight, the papers are in broad agreement about the data and even about its implications for theories of migration.
First, the consensus that underlies the current First Americans migration story: More than 20,000 years ago, a group of people came from Siberia to what was then the Bering land bridge between Asia and North America, now long drowned in the rising post-Ice Age seas. They lingered in this grassy, productive place, perhaps for a few thousand years.
Then, maybe driven away as their green land disappeared under water, they ventured south, probably along the Pacific coast. (My favorite theory is that these migrations were at least partly by boat.) By 14,600 years ago they had gotten all the way to what is today southern Chile, nearly to Patagonia. This is the well-dated inland site at Monte Verde. Impressive.
This means–and much genetic evidence now confirms it–that there was only one major Paleolithic migration from Asia to the Americas. However, there is a discombobulating genetic fact that both these papers wrestle with: detection of a bit of Australo-Melanesian ancestry in a few–but only a few–Native American groups, mostly in South America. Both papers end up accounting for this by suggesting that there may have been two migrations, not just one.
WHERE DID THAT AUSTRALIAN DNA COME FROM?
Note that neither of these papers postulates something so romantic (and unlikely) as a Kon Tiki-type voyage in reverse, paddling from the Antipodes eastward across the Pacific. Instead they rest their theorizing on the firmly established human inclination to wander and to procreate.
Because the Willerslev group found no trace of the Australo-Melanesian DNA in their ancient DNA samples, the Science paper argues that it may have arrived in the Americas relatively late–perhaps a migration to the Aleutian Islands (where this DNA is also found.) This journey is hypothesized to have taken place about 9,000 years ago. After which, I guess, the idea is that the Australo-Melanesian DNA then trickled southward, eventually into South America.
Seems like a bit of a stretch. I wonder especially about the (relatively) small number of ancient DNA samples studied. As we all know, because we have been told it so often, absence of evidence is not evidence of absence. Maybe the Australo-Melanesian DNA signal will appear in ancient American DNA too, when more of it becomes available?
But the Nature paper’s theory is also unappealingly intricate. Reich and his colleagues think those genes may be fairly ancient. They account for them by inventing a (conveniently) now-extinct East Asian “Population Y” that is only distantly related to today’s Andamanese, Australian and New Guinean populations.
But the American editions of these genes “cannot be due to a single pulse of migration south of the Late Pleistocene ice sheets from a homogenous source population.” Their suggestion: since it appears that genes from a Clovis burial are what are now thought of as classically Native American, try looking for the Australo-Melanesian genes in non-Clovis sites.
MAYBE THEY’RE NOT DUELING PAPERS AFTER ALL?
Are these two ideas really in such direct conflict, except maybe about how long ago those anomalous genes entered the Americas? They both cope by proposing a second migration.
What seems most intriguing to me is that both groups found the Australo-Melanesian DNA. So it is likely to be real, and it needs explaining. Maybe it would be better to view the two more as sparring papers rather than dueling papers, even though that makes this conflict somewhat less compelling and clickworthy.
Both papers also agree that the “Paleoamerican” model is wrong. That model, based on skeletal morphology rather than genes, argues that the true First Americans were Australo-Melanesians whose genes were swamped by later-arriving Siberians, as Gregory Cochrane explains at West Hunter.
At Embargo Watch, Ivan Oransky describes the maneuvering that Science and Nature went through to ensure that these papers got to journalists together. A very last-minute arrangement.
I wonder if that short lead time helps account for the media and blogging discussions of these papers, which I found unusually confused and confusing. It’s kinda defeatist, but I guess I’ll leave the last word to Razib Khan, whose exposition at Gene Expression was otherwise not terribly clear: “It is turning out that reality is crazier than our imaginations. Hold tight.”
WHAT’S-HIS-NAME IS SEARCHING FOR ALIENS
I suppose it’s really no puzzle why the media reception for Yuri Milner’s $100 million project to search for alien life treated the news as if the project was Stephen Hawking’s. See, for example, Rachel Feltman at Speaking of Science and Calla Cofield at LiveScience.
Who, after all, has ever heard of Yuri Milner? Even if he did have the public relations savvy to sign up Hawking (and other luminaries) and probably expected to be upstaged.
And I concede that Hawking’s endorsement raises an interesting question. He is known for his fear that ETs would be so far above us in accomplishments that they would sweep us into oblivion, regarding us as we regard bacteria. Why, then, does he want to search for them? It appears that he can’t stand not knowing. Life arose spontaneously on Earth, why not elsewhere?
Lots of detail from Jon Brodkin at Ars Technica. Much of the $100 million will go to buy telescope time on the 100-meter Robert C. Byrd Green Bank Telescope in West Virginia and the 64-meter Parkes Telescope in New South Wales, Australia.
At The Conversation, Jonti Horner will tell you everything about the history of the search for extraterrestrial intelligence and Andrew Norton will tell you everything about why it will be a waste of time.