"It was a substantial population, if only because it clearly persisted for 10,000 years or so," said Dennis O'Rourke, a University of Utah geneticist and co-author of an article published Thursday in Science magazine.
"The people would have been very adept at extracting resources. They were a very successful population or they would not have survived."
Scientists have long believed that the ancestors of North American aboriginals came from Siberia during the Ice Age, when massive glaciers covering most of the continent lowered sea levels enough to expose a vast stretch of land now called Beringia. Conventional wisdom has it that sometime between 25,000 and 15,000 years ago, the ancestors crossed Beringia, trekked an ice-free corridor down the West Coast and settled in various spots on a fresh new continent.
But a few things have never quite added up.
The genetic markers that make North America's aboriginals distinct from Siberians are up to 25,000 years old. But those markers didn't spread through the continent until about 15,000 years ago — a gap of 10,000 years.
Those ancient hunters and gatherers had to have spent those missing millennia somewhere that would both support them and isolate them from the Siberian genetic pool they were leaving behind.
O'Rourke and his two co-authors believe they may have found the answer in the seemingly unrelated field of paleoecology, the study of ancient environmental systems. Sea-floor cores from beneath today's Bering Sea show that Beringia — which stretched from Siberia to Canada's Mackenzie River — was not the barren, treeless tundra it was assumed to have been.
"There were these areas in Beringia that weren't steppe tundra, but were shrub tundra, where trees and shrubs and a variety of other plants and the animals that subsisted on them occurred," O'Rourke said.
"These (pockets) would have included a whole host of plant communities, small mammals, large mammals from mammoth to moose and elk. There would have been lots of animals to hunt."
Summer temperatures would have been about what they are today, although winters were colder.
O'Rourke suggests anywhere from a few hundred to a few thousand people lived in those more hospitable areas of Beringia as they drifted further and further from their genetic roots in Siberia over 10,000 years. When they finally resumed their eastward migration, they had become the ancestors of all modern North and South American aboriginals.
Archeologists haven't found any traces of those ancient people, but paleoecology has provided O'Rourke with an answer for that as well.
Evidence suggests the livable bits of Beringia were low-lying — exactly the areas that would have been submerged first during the post-Ice-Age melt. Present-day Alaska and Yukon are the uplands where humans would have hunted, but probably not lived.
"The paleoecology helps explain why there isn't an archeological record that reflects the genetic data," O'Rourke said. "That population was concentrated in refugia areas, which we now have reason to think were in the lowlands, the areas now under water.
"If we happen to be right about this, some coastal underwater archeology might not be untoward."
Quite apart from whether he's right, O'Rourke said he hopes his paper will encourage fellow scientists to think outside their disciplinary box.
"I was just not adequately familiar with the paleoenvironmental data and the implications of it," he said.
"It's my hope, and my co-authors as well, to get (scientists) to be more familiar with research that's coming out in different research streams, so that we do much more cross-disciplinary communication.
"I think that is going to lead us to some creative thinking."
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