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A Sunken Bridge the Size of a Continent

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Ilich
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« on: October 17, 2016, 11:00:14 pm »

Lately, though, it’s been colder. There are no climate models telling you that the Earth is changing; no maps telling you where to go. Perhaps you edge farther and farther from the ice sheets. Or maybe you follow the herds of caribou, bison, and other big game as they migrate toward food. Perhaps you head eastward, to places no one has ever been. You follow the rising Sun, your breath hanging in puffs of golden light in the morning air.

As you make your way across Beringia, you carry things: weapons, animal hides, babies on hips. It’s a slow journey; along the way, people die and are born. Maybe you reach a pleasant valley where game is abundant, and several families decide to stay. Others move on, seeking something better, until they can’t move on anymore. The way is blocked by ice. Some go back, until they, too, reach impassable ice.

It’s impossible to know the intricacies of the routes the migrants took to the New World. It wasn’t a single march or a mass migration, but a meandering dispersal across a vast and complex landscape. In all likelihood, these ancient Beringians honed their survival skills along the way, devising new technologies and tools. And if Tamm and her colleagues are right, they stayed so long in Beringia that it changed their genetic makeup. It became part of them.

John Hoffecker was deeply immersed in his own research when the Beringian standstill paper came out; he didn’t give it much thought to begin with. But a few years later, while working on a textbook about the evolution and dispersal of modern humans, he checked the paper again. It dawned on him: the Beringian standstill model accounted for the inconsistencies that had been nagging him for years. Researchers working in other disciplines were coming to the same conclusion—Beringia would have been habitable during the deep freeze, and ancient humans may have hung out there for thousands of years.

But proof in the form of artifacts or campsites remained elusive, and with good reason, says Hoffecker. “The obvious explanation for why we might not have archaeological sites dating to the Last Glacial Maximum is because, climatically, the mildest area [of Beringia] is now underwater,” he says.

The more Hoffecker thought about it, the more excited he got. Eventually, he had to talk to someone. He had long known Dennis O’Rourke, a prominent geneticist at the University of Kansas who studied genetic variation in the indigenous people of the Americas. And he knew O’Rourke was critical of the Beringian standstill model. Given his own giddiness, it was exactly what Hoffecker needed—someone who would bring him back to reality by pointing out all the problems with the hypothesis.

At the time, O’Rourke was working in the Arctic village of Kotzebue, Alaska, where cellphone service is spotty. He was walking from the airport when his phone buzzed. Hunching against the wind, he strained to hear the person on the other end. “And I’m rambling incoherently,” Hoffecker recalls, laughing. “I knew Dennis would be skeptical, and I was bracing myself. I remember him saying, ‘Well, it’s awfully convenient that these sites are all underwater.’”

O’Rourke saw other problems, too. If a small number of Asian families migrated into Beringia and were subsequently isolated there by ice sheets to the east and west, for example, their descendants would likely have experienced what is known as a population bottleneck—a drastic reduction of genetic variation detectable among their descendants. But there was little trace of such a bottleneck. In fact, a 2007 study led by Sijia Wang, then a PhD candidate at University College London, showed only a minor loss of genetic variation among indigenous Americans compared to the worldwide average—just six to seven percent.
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