Migration to America took long enough for evolution to happen on the way

Enlarge (credit: National Park Service)

The Bering land bridge plays a central role in our picture of how humans reached the Americas. When much more of the world’s water was locked up in ice, and the land between Asia and North America was exposed, people followed the bridge to migrate out of Asia, into Alaska, and from there into the rest of the Americas.

This picture tends to portray the bridge as purely a route to the new continents. In fact, the word ‘bridge’ definitely conjures up the wrong image. It was a geographic region, often called Beringia, and people lived there for so long that it probably would have been ludicrous to them that we could think of their home as transient. Current estimates suggest that people lived there for between 5,000 and 8,000 years, starting about 23,000 years ago.

That is a long enough time for natural selection to have had an effect on the genome of people who lived there, according to a paper in PNAS this week. The Beringians would have faced distinct diseases, food constraints, and climate conditions, and natural selection would have helped those with the right genetic adaptations to thrive in that environment. According to the new paper, we can see evidence of that natural selection in modern Native American populations.

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