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Beyond Stone & Bone

Swearing off DNA
by Mark Rose
September 24, 2009

Chickens_and_vase

With our January/February 2007 issue we began compiling and publishing a list of what we think are the top ten archaeological discoveries each year. Choosing them is an interesting exercise here at our office. We all have our favorites, and there’s always debate over whether some new find is really important or simply flashy. Now that the November/December issue has gone to press, we’re starting to think about this year’s list. For me, I like the discovery of a classical city in the suburbs of Istanbul, which I wrote about in an earlier post, and I like the Anglo-Saxon hoard that made headlines today. There’s also word out from Hierakonpolis, Egypt, of more amazing animal finds—think baby hippo—from the Predynastic cemetery there.

So 2009 looks like a good year. How does it stack up to earlier ones? You can have a look at our best from 2006, 2007, and 2008. That’s what I was doing when I noticed that each year’s list had a DNA related discovery, and in each case the findings were later contested.

In 2006, we included “China’s Guest Worker,” which reported that DNA analysis of human bones showed one of the workers who built the tomb of China’s first emperor was a Persian, likely a captive. This followed up an earlier interview (“Worker from the West”) with Victor Mair, who told us about the research that July. Yet it is quite possible that the Persian isn’t a Persian after all. As our July/August 2009 feature story “China’s DNA Debate” pointed out, this case shows that “DNA evidence, which often seems so clear and definitive, can be anything but, especially in China, where a lack of scientific transparency and concerns about the politicization of results have plagued recent efforts to provide a genetic perspective to ancient questions.”

The following year it was “Polynesian Chickens in Chile.” Who couldn’t like the idea of DNA proving that smart-looking blue-legged chickens were in South America courtesy of Polynesian seafarers? Radicarbon dates placed the chicken from between A.D. 1321 and 1407, before the arrival of the Spaniards. That was the conclusion, published in the June 2007 Proceedings of the National Academy of Sciences (PNAS), based on one of 50 or so chicken bones excavated at the site of El Arenal. You might think the combined evidence of DNA and radiocarbon dating would be pretty strong. But the problem is just one bone was tested. Results of a new study, which looked at more of the bones, were presented in the July 2008 PNAS. The DNA? It matched European chickens. The radiocarbon date? The bone was contaminated and the chicken wasn’t actually that old. Why did the chicken cross the Pacific? It didn’t.

Last year it was “American Genes,” which in part was about claims of human DNA being found in 14,300-year-old feces (coprolites) from Orego’s Paisley Cave, “the earliest direct evidence of human colonization of the Americas.” We covered it in depth in the feature story “Ancient Excrement” in our July/August 2008 issue. The research first came out in the journal Science on May 9th. This summer, the July 10th Science had comments by two groups of scholars who found fault with the study—actually, they just didn’t believe it. One said their own analysis of one of the coprolites was “difficult to reconcile with the DNA results identifying the coprolite as human.” The other questioned the DNA results, pointed out that the stratigraphy wasn’t intact and there were no diagnostic artifacts, and suggested that the radiocarbon dates are unreliable. (The original researchers responded to these criticisms in the same issue.)

So, I’ll be going back and adding editorial notes to these on the website (kind of like an asterisk in the baseball record books). Meanwhile, if you have your own favorite 2009 discovery you think should be in the list, let us know—unless it has something to do with DNA.

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About Our Blogger:

Heather Pringle is a freelance science journalist who has been writing about archaeology for more than 20 years. She is the author of Master Plan: Himmler's Scholars and the Holocaust and The Mummy Congress: Science, Obsession, and the Everlasting Dead. For more about Heather, see our interview or visit www.lastwordonnothing.com.

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