It was known that between 500 and 1000 years after Christ, the Mayans of Chichén Itzá, Mexico, performed human sacrifices to curry favor with the gods. But many details were unknown, particularly on the identity and origin of the individuals who were selected for this ritual, as well as on the reasons which motivated their choice. The analysis of DNA taken from the bones of these people who were sacrificed as offerings to the gods made it possible to clarify several of these mysteries, which are revealed today in an article published in the journal Nature.
The researchers took ancient DNA from the left temporal bone of 64 of the 106 individuals who were discovered in 1967 in a cavity — formed by a well and a cave — located near the pyramid of Kukulkàn, at Chichen Itza. These types of underground reservoirs, called chultúns, contained a cistern of water and represented for the Mayans a place allowing access to the kingdom of the gods.
Radiocarbon dating of the various bones revealed that human sacrifices took place for nearly 500 years at this location. The analysis of ancient DNA extracted from the temporal bone of these individuals showed that they were only young boys, aged three to six years old, several of whom (16 out of the 64) were close relatives, or even identical twins (homozygous) in the case of four of them. The ritual of sacrificing children was believed to bring rain and corn harvests.
“We believe that related male individuals were selected to honor the twin heroes Xbalamqué and Hunahpú, who in Mayan mythology avenged their father and uncle, themselves twins, who had been sacrificed by the gods. They avenge them by repeating cycles of sacrifice and resurrection in order to outwit the gods of the underworld,” explains the article’s first author Rodrigo Barquera, a postdoctoral fellow in the archaeogenetics department of the Max-Institut, by email. Planck of Evolutionary Anthropology (MPI-EVA), in Leipzig, Germany, and co-author Diana Hernández of MPI-EVA and the National School of Anthropology and History (ENAH) in Mexico.
Common genes and diet
The quantities of carbon and nitrogen measured in the collagen of the bones indicate that the sacrificed individuals had a very similar diet, “which suggests that the diet was part of the cultural elements used to prepare the individuals for sacrifice and that this preparation began long before the ceremony,” the researchers say. “The staple of their diet was corn,” but it also included “a wide variety of protein sources.”
The researchers also compared the genomes of the children found in the chultún to those of 68 contemporary Mayans living in the surrounding town of Tixcacaltuyub, as well as to ancient and contemporary genetic data from other populations in the region. They thus noticed “a genetic continuity” between the children sacrificed more than 1000 years ago and the Mayan population living in the region today. “In other words, this means that the ancient Maya of Chichén Itzá can be considered the direct ancestors of the Maya who live in Tixcacaltuyub today. And that the two populations are very similar, despite the mixture with individuals who were neither native to America nor locals, [lors de la colonisation] », Specify the authors.
Modeling suggests that the genome of the current inhabitants of Tixcacaltuyub is composed mainly (92%) of genes coming from indigenous peoples of America (the Mayans of Chichén Itzá), and also of a small European contribution, i.e. Spanish (7 %) and from Africa, i.e. Yoruba (0.03%).
Scientists also noticed that the Y chromosome of all the individuals recovered from the Chultún contained a set of genes (a haplogroup) from the Asians who populated the Americas. On the other hand, in half of the current inhabitants of Tixcacaltuyub, this haplogroup was replaced by another of European and African origin, “which testifies to the contribution of European and African males to the genetic pool of today’s Maya, and which indicates that there was a genetic exchange between these non-indigenous men and indigenous women of America,” emphasize Barquera and Hernández.
Immune variants
The study also highlighted an increase in the frequency of certain genetic variants associated with immunity among today’s Maya compared to what is observed among the Ancient Maya who were the subject of human sacrifice. . One of these variants confers resistance against enteric fever (also called typhoid and paratyphoid fever) caused by Salmonella enterica. This variant would have been selected during epidemics that occurred during the colonial period, notably during the cocoliztli pandemic of 1545. “Individuals who carried this variant in their genome were more likely to survive infection by Salmonella after the introduction of this pathogen into America [par les Espagnols] and pass it on to subsequent generations,” explain the two scientists.
“It has been demonstrated that during the 16th centurye century, wars, famines and epidemics caused population decline [indigène] potentially 90%. Infectious diseases, such as smallpox, measles, mumps, influenza, typhus, typhoid, enteric fever, rubella, whooping cough, diphtheria, endemic dysentery, fevers, such as malaria, and syphilis would have contributed to this decline in the population and would thus have led to the selection of genetic variants associated with immunity”, we recall in the article of Nature.
The researchers were also able to confirm that the caloric restrictions experienced by the first humans to arrive in America allowed genetic variants allowing more efficient lipid metabolism to be selected and to increase in frequency among Native Americans. And as these variants favored higher blood levels of cholesterol in situations of scarcity, they also made it possible to increase the biosynthesis of sex hormones (which depend on cholesterol metabolism) and thereby fertility, explains Mr. Barquera.
“With the introduction of farm animals from Europe, the cholesterol intake in the diet of the Natives increased rapidly. These variants then became useless and they would explain why today’s Indigenous people are more affected by the Western diet,” he continues.
In addition to revealing new details about these human sacrifices practiced by the ancient Maya, this genetic study has shed light on the genetic history of these indigenous people of Yucatán who formed a flourishing society more than 1000 years ago and whose we can still admire the remains.