All indigenous Americans might be able to trace back their ancestry to just a few hundred people who made that first migration into the New World, a new study has revealed.
Publishing their work in Genetics and Molecular Biology, researchers have been sampling the genetics of people living along the likely path that humans took when migrating from Asia to the Americas. These included people in China, 10 Siberian groups, and 10 Native American populations going all the way through Central and South America.
They then sequenced the DNA from nine independent, non-coding regions of the genomes spanning a period of 15,000 years, before analyzing them to get an estimate of how many humans likely founded the Americas, finally settling on around just 250 individuals.
The work feeds into earlier work that found that all indigenous people in the Americas were descended from a unique group of people known as the Ancient Beringians. Researchers now think that starting around 23,000 years ago, humans moved onto the Bering land bridge, where they became genetically isolated from those in Asia. When the glaciers retreated from Canada around 13,000 years ago, a corridor opened up allowing some to pass through into the untouched Americas.
“It wasn't a matter of a group that announced, ‘Let's go follow this one,’” explained Michael Crawford, who co-authored the paper. “It was a matter of population fission among hunters and gatherers. There would be about 50 people, and when the population's fertility gets higher and higher, the population splits into the next so-called 'county' and then the next.”
It seems extraordinary that the roughly 69 million indigenous people of the Americas can trace their origins back to just 250 people who made those pioneering first steps into the New World. But let’s not forget that every single person outside of the African continent – all 6.2 billion of them – are descended from just a handful of modern humans who were lucky enough to survive the migration out of Africa around 120,000 years ago.
The picture with the rest of the world is, admittedly, complicated by the addition of Neanderthals, Denisovans, and most probably some other archaic species yet to be pinpointed who were already doing their thing in the wider world, but the principle is still largely the same.
These early populations all went through significant genetic bottlenecks, meaning that traits that might ordinarily be rare in the wider population can then become over-represented in the new environment. While this can sometimes mean that harmful conditions become common, it can also mean the reverse, and useful adaptations are rapidly spread through a population.
For example, it was recently found that the first North Americans likely carried with them a gene variant that made women produce a larger amount of more nutritious milk, which enabled the developing babies to get enough nutrients to survive the harsh conditions these early folk faced. Nowadays, every indigenous American has the same gene variant.
This latest work helps shed some light on exactly how these early migrations took place, and how they went on to rapidly conquer the Americas.
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