How many people did it take to cross the land bridge from Siberia to populate the North American continent? Jody Hey, a genetics professor from Rutgers - the state University of New Jersey in the U.S.A. - claims that it took as few as seventy people to become the first Native Americans. Perhaps it was a single small tribe that struck out on its own from an ancestral population in Asia numbering no more than 9,000 people.
     The professor developed a computational method that uses genetic information to create models of population divergence - where a group has split off from its ancestral population to pursue its own destiny. Hey focused on one of the three major language groups in North America - the Amerind speakers - who are believed to represent the earliest people who ventured across an ancient land bridge from Siberia into Alaska and then deep into the continent.
     In addition to population size, using rigorous and complex methodology the date of the divergence can be obtained. By Hey's calculations, the wanderers reached North America between 7,000 and 14,000 years ago, more recently than the 15,000 years suggested by archeological evidence, several experts said.
     Calculations show that the original seventy made up only about 1% of the effective population size. 'Effective size' is about one third of the 'census population size' which in this case comes to about 200 people.
     "The small number is surprising to me," said anthropologist Joanna L. Mountain of Stanford University. "We may be looking at the winners here. It is quite likely that other groups came over and did not survive." If the original settlers were so few, "that would be quite striking," said Theodore G. Schurr at the University of Pennsylvania's Laboratory of Molecular Anthropology. "It would have a lot of biological and medical implications."

Sources: EurekAlert!, Los Angeles Times (23 May 2005)