Jan Bartek - AncientPages.com - Scientists have analyzed ancient DNA from pre-Hispanic individuals in northern and central Mexico, revealing contributions from an unknown “ghost” population.
The result of the study provides surprising information about the migration patterns of ancient Mexican civilizations. As explained in the study published in the journal Science, ancient DNA has revealed much about human populations' movement and genetic legacy. However, due to climatological restrictions, DNA is notoriously sensitive to degradation in hot climates, resulting in a greatly imbalanced study of regions and ancestries.
Population continuity and ghost genetic ancestries in pre-Hispanic Mexico. Ancient individuals who inhabited the northern frontier of Mesoamerica (NFM) before and after a 200-year period of severe droughts (shown in timeline) belong to a continuous population. This is in contrast to a previous hypothesis suggesting that hunter-gatherers from Aridoamerica replaced the populations at the NFM following the southward shift of its limits with Mesoamerica (solid and dashed lines). Individuals from Sierra Tarahumara and Cañada de la Virgen show genetic ancestry from two distinct ghost populations (UpopA and UpopA2). Credit: Science (2023). DOI: 10.1126/science.add6142
Between 1100 and 900 years ago, a global warming episode affected numerous civilizations worldwide. In the Americas, severe droughts reconfigured the demography of pre-Hispanic civilizations and the ecological landscape.
Based mostly on archaeological evidence, previous studies suggested that before European colonization, droughts shifted the border southward between desertic Aridoamerica and the verdant and culturalally rich Mesoamerica, home to large civilizations like the Aztecs and Mayans. This climate change allegedly led to a population replacement in the northern frontier of Mesoamerica by seminomadic hunter-gatherers from Aridoamerica.
The research team wanted to learn more and generated ancient genomic and mitochondrial DNA data to test the theory surrounding the migration of ancient peoples in Mexico. An analysis of DNA samples going back approximately 2,300 years provided more answers seeing new light on the ancient history of Mexico.
"We leveraged these data to describe the ancient population structure of Mexico and to investigate the contribution of unsampled genetic lineages to the ancient genomes," the research team explained in the study.
Paleogenomic approaches to study the demographic history of pre-Hispanic Mexico involve the analysis of ancient human DNA collected from archaeological sites. Shown are ruins in Toluquilla.Photo: Especial Notimex/newsroom
"The pre-Hispanic population structure closely resembles the structure observed in present-day Mexico, which clearly differentiates northern and central Indigenous populations. This reflects an overall conservation of the genetic structure of the populations inhabiting the Mexican territory for at least 1400 years (which is the date of the most ancient individual in our study).
People Did Not Migrate Despite Long-Standing Droughts
We found genetic continuity in the ancient individuals from before and after the climate change episode. This contradicts the hypothesis of population replacement by Aridoamerican groups in this region and suggests that the local population stayed in their homeland despite the long-standing droughts. The population continuity at the studied site can be explained by the favorable location in the high and humid Sierra Gorda mountain range and the fact that cinnabar mining was the main economic activity, not agriculture.
We identified the contribution of two distinct unsampled “ghost” genetic ancestries to pre-Hispanic populations of northern and central Mexico, respectively. Whereas the unsampled genetic ancestry contributing to the northern genome coincides with one previously identified in a present-day population from south Mexico, the second ghost genetic ancestry was previously unknown.
The ancient genomes revealed a conservation of the genetic structure in Mexico in the past 1400 years and population continuity in the northern frontier of Mesoamerica despite the severe droughts 1100 years ago. It is likely that the mining-based economy allowed the population to subsist in their homeland during this climate change period when the border between Aridoamerica and Mesoamerica shifted southward.
The identification of a new ghost genetic ancestry (UpopA2), along with that observed in ancient Sierra Tarahumara and present-day Mixe (UPopA), reveals a complex population history in the late Pleistocene in the Americas. The recovery and study of ancient genomes from Mexico, conducted ethically, can help fill important gaps in our understanding of the deep population history of the Americas," the scientists write in this study.
It is unknown why northerners had not migrated south when conditions grew dry. One explanation could be people stayed because of cinnabar commerce.
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"The main subsistence strategy in Toluquilla and Ranas was the mining and trade of cinnabar, a valuable mineral of sacred value in pre-Hispanic cultures . We hypothesize that the cinnabar trade and the landscape of the Sierra Gorda allowed the peoples of Toluquilla and Ranas to subsist despite low rainfall conditions during the drought," the research team concluded.
The study was published in the journal Science
Written by Jan Bartek - AncientPages.com Staff Writer
