SANTA CRUZ DE TENERIFE, May 17. (EUROPE PRESS) –
The magazine ‘Science’ has just published the study ‘Demographic history and genetic structure in pre-Hispanic central Mexico’, in which remains of ancient DNA have been analyzed, showing that the population of the Central American country endured severe climate change that occurred a millennium ago , characterized by severe droughts.
The study has been led by Viridiana Villa Islas and María Ávila Arcos, from the National Autonomous University of Mexico, and has had the participation of professor and researcher Rosa Fregel, from the Department of Biochemistry, Microbiology, Cellular Biology and Genetics of the University de La Laguna, together with researchers from other institutions in Mexico, Denmark, Sweden, the United States, Germany, France and Spain.
The study points out that between 1,100 and 900 years in the past there was an episode of global warming that affected numerous civilizations, which in America led to severe droughts that reconfigured the demography of pre-Hispanic civilizations, as well as the ecological landscape. The study has used ancient genomic data from twelve pre-Hispanic individuals from before and after this episode of climate change to investigate the population dynamics at the border between the two biocultural regions of Aridoamerica in the north and Mesoamerica in central and southern Mexico.
Archaeological evidence indicates that droughts pushed the border south between desert-like Aridoamerica and green, culturally rich Mesoamerica, which was home to great civilizations such as the Aztecs and Mayans. This climate change supposedly caused a replacement of the population on the northern border of Mesoamerica by semi-nomadic hunter-gatherers from Aridoamerica.
However, this hypothesis is based solely on archaeological data, so the researchers in this project have generated ancient genomic and mitochondrial DNA data to test it. In addition, these data have been used to describe the ancient population structure of Mexico and to investigate the contribution of unsampled genetic lineages to ancient genomes.
The pre-Hispanic population structure is very similar to that observed in present-day Mexico, which clearly differentiates the indigenous populations of the north and the center. This reflects a general conservation of the genetic structure of the populations that inhabit the Mexican territory for at least 1,400 years (which is the date of the oldest individual in the study).
The research team has found genetic continuity in the ancient individuals from before and after the climate change episode, which contradicts the hypothesis of population replacement by Arido-American groups in this region and suggests that the local population remained in their territory despite the prolonged droughts. This continuity can be explained by the favorable location in the high and humid Sierra Gorda and by the fact that cinnabar mining was the main economic activity, not agriculture.
GHOST POPULATIONS
The contribution of two ‘ghost populations’ in the pre-Hispanic populations of northern and central Mexico, respectively, has also been identified. This is the name given to those genetic ancestors that have not yet been characterized from a molecular point of view (there is no direct information available on their DNA), but whose contribution can be detected using statistical methods. An interesting result has been that, while the unsampled genetic ancestry contributing to the northern genome coincides with one previously identified in a current population of southern Mexico, the second comes from a hitherto unknown phantom population.
In this way, the ancient genomes revealed a conservation of the genetic structure in Mexico in the last 1,400 years and a continuity of the population in the northern border of Mesoamerica despite the severe droughts of 1,100 years ago. It is likely that the mining-based economy allowed people to subsist in their homeland during this period of climate change when the border between Aridoamerica and Mesoamerica moved south.
The identification of a new phantom genetic ancestry, along with that observed in the ancient Sierra Tarahumara and present-day Mixe, reveals a complex population history in the Late Pleistocene of America. The recovery and study of ancient genomes from Mexico, conducted in an ethical manner, can help fill important gaps in our understanding of the deep population history of the Americas.
