BOSTON, Mass. (Dec. 21, 2008) -- Modern humans left Africa over 60,000 years ago in a migration that many believe was responsible for nearly all of the human population that exist outside Africa today.

Now, researchers have revealed that men and women weren't equal partners in that exodus. By tracing variations in the X chromosome and in the non-sex chromosomes, the researchers found evidence that men probably outnumbered women in that migration. The scientists expect that their method of comparing X chromosomes with the other non-gender specific chromosomes will be a powerful tool for future historical and anthropological studies, since it can illuminate differences in female and male populations that were inaccessible to previous methods.

While the researchers cannot say for sure why more men than women participated in the dispersion from Africa--or how natural selection might also contribute to these genetic patterns--the study's lead author, Alon Keinan, notes that these findings are "in line with what anthropologists have taught us about hunter-gatherer populations, in which short distance migration is primarily by women and long distance migration primarily by men."

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These findings were published Dec 21, 2008 online in Nature Genetics.