Founding fathers

The Americas were originally colonized by "a band of just 70 hardy explorers and their families," according to a new genetic study, as reported on Nature.com:

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.

"The number of founders might be a surprise to some, although we knew that there was a bottleneck of some magnitude," says Jody Hey of Rutgers, the State University of New Jersey, who carried out the study. The fact that the most plausible way on to the American continent involved a trek through the frozen north probably meant that few attempted the journey.

That's not to say all Native Americans are descended from that original group. As Hey acknowledges, there are several possible scenarios that his study doesn't cover, including subsequent migrations from Asia, or continued contact and intermarriage between populations of the continents.