Aztec Conquest Altered Genetics; 'Apocalyptic' Disappearance of Otomies Explained

Centuries ago, Xaltocan was inhabited by the Otomi people. They lived in the pre-Aztec Mexican city-state for centuries before abruptly vanishing. Researchers have wondered for years whether they assimilated with the Aztecs, or merely abandoned the town altogether. Now, they may have their answer.

New anthropological research from the University of Texas at Austin, Wichita State University and Washington State University show that the answers may lie in DNA. The researchers used ancient DNA (aDNA) sampling in order to test whether the original Otomies may have intermarried with the influx of new residents. They used the aDNA taken from 25 bodies that were recently recovered from patios outside excavated houses in Xaltocan. They found that the pre-conquest maternal aDNA did not, in fact, match those of the post-conquest area. This shows that the Aztec conquest of the town had a significant genetic impact.

Historical documents suggest that most residents fled Xaltocan in 1395 AD when the Aztecs first invaded the site. Subsequently, the Aztec ruler at the time sent taxpayers to resettle the site in 1435 AD. However, archaeological evidence suggested some degree of population stability across the imperial transition--this would indicate that perhaps the original residents did not all flee.

The new findings, though, show that the massive genetic shift means that many of the Otomies did indeed flee the site. The ones that did stay probably intermarried. The lead author of the study, Jaime Mata-Miguez, theorizes that long-distance trade, population movement and the reorganization of many conquered populations caused by Aztec imperialism could have caused similar genetic shifts all across Mexico.

Since the study only traced the history of maternal genetic lines at Xaltocan, future aDNA analysis is needed to clarify the extent and underlying causes of the genetic shift.

The study was published in American Journal of Physical Anthropology.