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See Inside September 2008

Mammoth Sequences: A Hunt for DNA from the Extinct Titans of the Klondike

Duane Froese and Ross MacPhee on an excavation dig to collect material that might hold Pleistocene genetic clues to mammoths



Charles Q. Choi

Dawson City, Yukon—After revving up with a roar, a core drill designed to punch holes in concrete begins digging into ice more than 100,000 years old. Here in the Klondike, the drill serves as a kind of gas-powered, handheld time machine, bringing up frozen earth from the Pleistocene, when mammoths and other megafauna once ruled. In a land where miners still hunt for gold, paleomammalogist Ross Mac­Phee of the American Museum of Natural History in New York City and his colleagues seek a different kind of treasure—DNA from extinct titans.

Millennia ago, as the earth in the Klon­dike cracked during the springtime thaw, water leaked in, only to freeze again during winter to form wedges of ice, explains geologist Duane Froese of the University of Alberta. Dripping in with this water was sediment from the surface, which might hold DNA from mammoths, as well as that of the plants, bacteria and other life once found in the region, MacPhee says. Nothing is known about the genetics of mammoths from the middle Pleistocene, and such DNA could elucidate their evolution. The researchers hope to find clear evidence that two species of mammoth, not just one, roamed the Americas at the end of the last ice age.

This area, dominated today by spruce forest mixed with paper birch and aspen trees, was once part of Beringia, the grassland steppe ranging from North America to Asia that nowadays lies submerged under the icy Be­ring Strait. Froese has worked in the Klondike for the past 15 or so field seasons, aiming to reconstruct a full picture of Beringia over the past few million years. Sampling trapped sediment for DNA could prove a far easier way to analyze how Be­ringia’s ecosystems shifted over time as compared with attempting to collect hundreds of fossils from different taxa.

In joining the team for seven days in June, I learn that ancient DNA molecules are not the only clues the researchers seek here. Paleoentomologist Svetlana Kuzmina of the University of Alberta sifts through sediment for fossil insects—by studying where modern examples of these now dwell, she can extrapolate what the climate might have been like back then. Lee Arnold of the University of Wollongong in Australia will scan crystalline grains to pinpoint the ages of all the finds, thus helping to reveal the proper sequence of events—which is as important as having words in the right order in a sentence. And later the scientists will head north by plane, helicopter and boat to dig for bones.

The fact that gold mining continues in the Klondike has proved invaluable. We can drive over mining roads right up to sites, as opposed to lugging heavy equipment a mile or more by foot. The miners have also been very supportive, even using excavators to scrape off tons of surface material, called overburden, from the frozen earth at a rocky site named Paradise Hill. Their help makes research far more cost-effective, Froese explains. MacPhee agrees: “You’d be lucky to get one site done in Siberia in a week.”

Still, fieldwork remains a hard, dirty task. The giant wedge of ice we mine at Gold Run Creek on the fourth day of our ex­pedition was hidden under a slope of powdery muck—silt loaded with ancient, decomposing organic material, which smells much like manure. As we expose the ice to the sun, water mixes with the muck to form a slippery ooze that occasionally traps us up to our thighs, much to our chagrin. Field time also can unpredictably vanish, as we discover when the rough, gravel roads take their toll on the rental SUV, which suffers three flats in just two days.

In the end, all the hard-won scientific treasure could help solve key mysteries. MacPhee hopes, for instance, that the DNA could explain why so many megafauna went extinct in the Americas. Did rapid swings in climate kill them off? Or was it the cunning of human hunters? Or was it species-jumping plagues that humans brought over, as MacPhee suggests?

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