Americas had seventy 'founding fathers'
Gene study counts the first humans to reach the New World.
The first people to colonize the Americas were a band of just 70 hardy explorers and their families, a genetic study suggests. Analysis of Native Americans' genes shows that their ancestors represented just a tiny fraction of the Asian population at the time.
This intrepid group is thought to have made the arduous journey across a long-lost land bridge between Siberia and Alaska about 14,000 years ago. The research suggests that this entire group might have numbered just 200 people, since experts generally expect populations to be about three times the size of the group that ultimately pass on their genes.
To test the theory, Hey analysed data from DNA samples previously collected from Amerind-speaking Native Americans, and from populations in northeast Asia. He compared the amount of variation in nine sections of their DNA to estimate the size of the founding population.
At the time, the Asian group had an 'effective population' (the number of reproducing adults) of around 9,000, Hey calculates. But the effective population of the Amerind group was less than 1% of this, he reports in the journal PLoS Biology1.
Far and wide
Once established in the New World, humans are thought to have made short work of spreading across its continents. Archaeological evidence from Monte Verde in Chile suggests that humans reached South America within a few centuries of their arrival in North America2.
The idea that they did this from such modest beginnings makes that achievement all the more impressive. But Hey points out that his study may not tell the whole story. His analysis did not include samples from other Native American populations in the northern reaches of the continent such as Aleuts, who are believed to have arrived there much later than the Asian immigrants.
He is also unable to say whether any of the New World's founders travelled back to mate with Asian people, or whether the original band were followed generations later by subsequent waves of migrants. But he does know that, once the first group reached America, their numbers boomed in just a few generations, and the effective population increased by an order of magnitude.
Hey hopes that his model can be used to investigate other situations in which a human population broke off to colonize a new area, such as the peopling of Australasia. "This approach could provide a detailed portrait of historical populations," he says.
- Hey J., et al. PLoS Biology, 3. e193 published online at plosbiology.org (2005).
- Fiedel S. J. J., et al. Archaeol. Res., 8. 39 - 103 (2000).