Did the first people to inhabit the Americas hug the coast after crossing the Bering Strait or travel farther inland, between two massive ice sheets?
This question has dogged researchers for decades. Now, a review of archaeological, geologic, anthropological and genetic data argues for both, but especially for the latter: It appears that prehistoric humans favored the inland route, although some traveled along the so-called coastal kelp highway later on, the new review says.
But not everyone is convinced this is the case. Some recent studies have suggested that the coastal route was the preferred path. That's because inland conditions were far too harsh until the ice sheets receded, which some research suggests did not happen until after the first settlements in America were founded. [In Images: Ancient Beasts of the Arctic]
The first Americans began their journey in northeast Asia and southern Siberia. Then, between 25,000 and 20,000 years ago, the ancestors of today's Native Americans split off from East Asians, according to the new review.
What happened next is hotly debated. It's possible that this group immediately traveled across the now-submerged Bering Strait land bridge, or that they hung out in Beringia — a concept known as the Beringia standstill hypothesis. Beringia is the term used to describe what then would have been a massive region encompassing parts of Russia, called western Beringia; Alaska, called eastern Beringia; and the ancient land bridge between the two.
The review authors have yet another idea: Maybe this group stayed in northeast Asia, but in a way that led the group to become genetically isolated from other populations there. Then, after they traveled across the land bridge and reached Alaska, the people would have been able to travel inland for the most part through a new ice-free route. (Scientists disagree about when this ice-free route opened, however.)