DNA study finds first Americans arrived in waves

Geneticists have discovered the earliest Americans arrived on the continent in three separate waves, refuting the longstanding belief in a one-time migration across the Bering Strait.

The discovery adds further complexities to the understanding of America’s migrant history. The dominant theory it challenges offered a much simpler explanation of North and South America’s earliest populations.

By conducting the largest survey of Native American DNA, geneticists were able to compare their genomes with DNA samples from nearly 500 people in various Siberian populations. A report of their findings was published last week in the journal Nature.

“What we find is that the patterns we see in the data can’t be explained by the hypothesis that there’s a single, ancestral population to all Native Americans,” said David Reich, a genetics professor at the Harvard Medical School and co-author of the report. “If that was the case, all Native Americans today would be related in the same way to present day Siberians, but that’s not true.”

The previous theory held that the first Americans arrived across a land bridge between Siberia and Alaska more than 15,000 years ago.

While most Native American populations came from that first wave, Reich says, many groups in northern North America showed a combination of all three.

“When the later waves of migration came to the Americas, they weren’t entering an empty landscape,” he said. “They were entering a landscape filled with people already. And instead of just replacing or displacing the people they met, they actually mixed with them in a profound way.”

The discovery could have profound implications in disease research, allowing scientists to better predict genetic health risks among different populations. Understanding how people around the world are related to one another is a key step in that process.

“This certainly makes progress in that direction,” Reich said.