Analysis of grave sites from pre-Hispanic times in Southwest United States has revealed a disproportionate sex ratio in the favor of women during periods of high violence, pointing how prolonged warfare influences demographics.

This study is the first to research the demographic movement of women in pre-Columbian America.

"Warfare is common in small- and intermediate-scale societies all over the world, now and in prehistory. Capturing women was often either a goal, or a by-product, of such conflict," says archaeologist Tim Kohler (Washington State University),

Kohler and Kathryn Kramer Turner (U.S. Forest Service) studied 1,353 human remains from ancient grave sites in one of the most renown pre-Columbian sites in North America, belonging to Pueblo culture : the awesome 11th-century ruins in Chaco Canyon, New Mexico, and a related 13th-century site to the north called Aztec (photo).

Meanwhile, the researchers observed that many sites from the same time period in the Mesa Verde region in Southwest Colorado ( just north of the Aztec site) revealed a much lower women ratio than they should.

The imbalanced ratio between women and men could have been provoked by non-coercive movement, like women migrating toward elites or the recruitment of women as specialized guild producing prized stuffs, such as jewelry or pottery.

But this unusual phenomenon is correlated with a time of high young men mortality, pointing towards a war period.

"Given the mirror symmetry of their sex ratios in the 1200s and the elevated death rates among young people in both areas, we suggest that societies in the Totah (which encompasses the Aztec site) obtained these women from Northern San Juan societies to the northwest through raiding and abduction," said Kohler.

Another signs also would indicate that many women were war prisoners or enslaved: some in the Aztec area were not buried in the usual respectful manner and many of the women bones carry signs of an abused life.

Photo credit: Tim Kohler