Before colonization, today’s Mexico was divided into Aridoamerica and Mesoamerica. In each region lived different peoples who were dedicated to different activities. In the first, in the arid north, the pre-Hispanic peoples were hunters and gatherers. In the second, center and south of the country, the largest civilizations were established, which survived thanks to agriculture. The border that divided them has been the subject of study for decades. Until now, the idea prevailed, based on archaeological evidence, that this dividing line had moved south because groups living in Mesoamerica had to migrate forcibly because of a drastic climate change that occurred approximately a millennium ago.
However, a new study of ancient DNA from these populations has led to the discovery of the same genetic traces, before and after several centuries of mega-droughts, and has opened the door to an option: that some Mesoamerican peoples had not moved, but rather that they had adapted to new forms of life in the face of the lack of water. This resistance and ability to adapt calls attention to the serious political crisis that later caused great droughts in the Mayan civilization, which had also led to the collapse of empires such as the Hittite in Antiquity.
The genetic diversity of pre-Hispanic peoples shows broad continuity for at least the last 2,300 years and still survives in populations in Mexico today. The current indigenous groups of the country maintain similarities in their DNA with that of the ancient inhabitants. This genetic correspondence has been one of the conclusions of the study Demographic history and genetic structure in pre-Hispanic central Mexicopublished today by the magazine Science, and that helps to understand a little more about the demographic movements that ancient societies lived through. A group of scientists have carried out the largest genetic study ever done on the ancient peoples of Mexico, which has shed some light not only on the present, but also on the Mexican past.
The hypothesis that some Mesoamerican peoples had been displaced due to climate change was formulated from anthropological studies. But the genetic review of 27 samples from different pre-Hispanic individuals, taken at eight archaeological sites, suggests something different. The specific analysis of some remains of the Sierra Gorda, located in central Mexico and on the northern border of Mesoamerica, suggests that the population that inhabited that place did not migrate when the droughts occurred between 900 and 1,300 after Christ. “Individuals from Sierra Gorda before and after the drought shared a greater genetic drift with each other than with any other pre-Hispanic individual,” the researchers say in their article.
One of the co-authors of the study, María Ávila-Arcos, from the National Autonomous University of Mexico (UNAM), explains that although the droughts could have affected other populations, this was not the case for the civilization that inhabited the Sierra Gorda. , which remained in the place where he resided. “In the site that we studied, population replacement did not occur. The continuity was reflected, ”she says in a telephone interview. The publication points out that a possible explanation for this continuity “is that the favorable climatic conditions in the north of Sierra Gorda have maintained higher humidity than other arid places on the northern border of Mesoamerica.”
Another factor that scientists believe could have helped the inhabitants of the Sierra Gorda to survive, specifically those who lived in the current archaeological sites of Ranas and Toluquilla, is that many were engaged in the trade of cinnabar or cinnabarite, a mineral that had a sacred value for pre-Hispanic cultures. “We hypothesize that the cinnabar trade and the landscape of the Sierra Gorda allowed the towns of Toluquilla and Ranas to survive despite low rainfall conditions,” the document states. The researchers admit, however, that there are factors that suggest that they could have suffered a strong population reduction due to climate change.
The analysis carried out by UNAM scientists, together with researchers from academic institutions in Sweden, Denmark, the United States, Spain, Germany and Australia, explains how the migratory movements of ancient Mexican civilizations have been much more complex than expected. One of the points they point out, for example, is how the DNA between the Mesoamerican peoples was linked to each other; or the genetic flow between populations of Mesoamerica and Aridoamerica. Another of the correlations they draw is the line of continuity between the Pericúes, who lived in the Baja California peninsula and disappeared in the 18th century, and the Pima people (also known as Akimel O’odham), who currently live between Arizona, Sonora and Chihuahua.
A collateral finding that researchers have had, who have used databases of genomes that already existed, has been that of two ghost towns. Two societies that had not been mapped so far. One of these genetic contributions, which scientists have named UpopA and which they estimate was a community that separated from Native Americans some 24,700 years ago, has also been found in the genome of current populations in northern Mexico, as well as in the Pueblo Mixe, from the south of the country. The other ghost genes (UpopA2) were identified in the Rarámuri community of the Sierra Tarahumara. These lineages raise questions about how these exchanges occurred. “There are more questions than answers, what it does let us see is that the process of population of America was quite complex,” concludes Ávila-Arcos.
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