Women on the move

The conventional wisdom that men have spread their genes across the world as they traveled for war, exploration, trade or work turns out to be wrong. Instead, over the course of history, women's genes have traveled more widely across the globe as they have married and gone to live with their husbands' families. "Differences in migration rates between men and women can be measured by studying their genes," says Mark Seielstad, who wrote a Ph.D. thesis about the topic three years ago. Seielstad is now a research associate at the Harvard School of Public Health's Program for Population Genetics. "Such measurements reveal that, when it comes to exchanging genes among populations, women's movements have been more important than those of males." Seielstad's thesis, published in 1998, presented the first detailed evidence that women have played a more important role than men in spreading new genes around the world. Since then, Seielstad and colleague Nadia Singh have also used this technique to date the arrival of the first people in the Americas. From tracking genes that appear in Native Americans only, they conclude that migrants reached North America from Asia not more than 20,000 years ago, as much as 20,000 years later than the maximum date determined by earlier and less accurate analyses.