In the spring of 1967, workers building a small airport behind Chichén Itzá, Mexico’s ancient Mayan city, ran into a problem: Their excavations had uncovered human remains in the path of the proposed airstrip. The airport was intended for tourists who wanted to visit Chichén Itzá. But the proximity of the remains to an important archaeological site forced work to stop until the bones could be examined.
Any hope of a quick resolution was dissolved when archaeologists who responded to the site discovered a chultún, an underground container for storing rainwater that, in Mayan mythology, was considered the entrance to the underground land of the dead. Connected to the chultún was a cave containing more than 100 sets of human remains, almost all belonging to children. In an effort to finish the airport, researchers had only two months to excavate and exhume the cache of bones.
Nearly 60 years later, ancient DNA extracted from 64 of the children offers new insights into the religious rituals of the ancient Maya and their links to modern descendants. In a paper published Wednesday in the journal Nature, an international cohort of researchers reveals that the children – victims of sacrifices killed between 500 and 900 AD – were all local Mayan males who may have been specifically selected to be killed in pairs of siblings.
“These are the first ancient Mayan genomes to be published,” said Johannes Krause, an archaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. The DNA work provided unprecedented insight into the identities of the sacrificed children. “You are very moved by a finding like that,” Dr. Krause said, noting that he himself has a young son.
The search for the genome of Mayan children did not begin as an exercise in ancient Mayan rituals. In the mid-2000s, Rodrigo Barquera – currently an immunogeneticist at the Max Planck Institute – hoped to discover the genetic legacy of the deadliest pandemic in Mesoamerica.
In 1545, an outbreak of Salmonella enterica spread like wildfire across what is now Mexico. Over the next century, the disease killed up to 90% of the indigenous population. Pandemics of this type often leave their mark on the immune genes of survivors. To uncover this genetic legacy, Dr. Barquera and his colleagues needed to compare the DNA of precolonial remains with that of people born after the calamity.
The children found in the chultún were part of a pre-Columbian group that had certainly never faced the pandemic in their lifetime. So in 2015, the team received permission to destroy a small part of their skulls to sequence the DNA.
The team first used the DNA to determine the sex of the children as part of routine sequencing. The skeletons of people under a certain age do not offer much information about biological sex, so this aspect of children was a mystery.
It took a year for the first results to arrive, and when they did: “Wow,” Dr. Barquera said.
The 64 skulls belonged to males. “We kept repeating the tests because we couldn’t believe they were all boys,” she said. “It was incredible.”
The first archaeologists who studied the Mayans proposed that the culture was concerned with sacrificing young, virgin women. This theory has been called into question in recent decades when it was discovered that the majority of people sacrificed in the sacred cenote – a natural sinkhole in Chichén Itzá – were children.
“This obviously contradicts the argument that the majority of people thrown into the cenote were young, virgin women,” says Jamie Awe, an archaeologist at Northern Arizona University in Flagstaff, who was not involved in the study. The obsession with virgins in archaeological circles most likely arose from a combination of colonial ideas and limited data, she said.
DNA now confirms that the chultún children were all boys, he said, adding: “We wouldn’t have known who they were if the DNA study hadn’t been done.”
Later genetic testing also showed that many of the children were related to each other, and among them were two sets of identical twins. According to Dr. Barquera, it is unknown why they were chosen for sacrifice. But it is possible that the brothers, or close relatives, were selected to reflect the trials of the Hero Twins, key figures in Mayan cosmology who went through cycles of sacrifice and rebirth.
“Rituals from ancient times tend to be particular,” Dr. Awe said. “This study indicates that, for some religious ceremonies, it was important that only male children be selected for sacrifice.”
Dr. Barquera and his colleagues discovered that children are returning to the modern Mayans living around Chichen Itza. The team compared the children’s DNA with that of the Mayans living in Tixcacaltuyub, a town about an hour’s drive from Chichén Itzá, and found strong genetic continuity between the two groups. As Dr. Barquera expected, the pandemic of 1545 left its mark on the Mayans, bequeathing the residents of Tixcacaltuyub at least one genetic variant associated with immunity to salmonella.
Dr. Barquera and some colleagues traveled to Tixcacaltuyub to share their findings in local schools and with study participants. They also shared previous genetic work done by other groups that indicated that the ancestors of the Mayans first moved to the region about 9,000 years ago. Taken together, the genetic work suggests that the peninsula’s large population experienced few migrations or genetic exchanges since the first ancestors of the Mayans moved to the area.
The DNA provides “clear evidence that these people are descendants of those who developed one of the world’s most accomplished civilizations,” Dr. Awe said.
Dr. Barquera added that study participants were delighted to receive confirmation that they were genetically related to the builders of Chichen Itza.
“People who live near these archaeological sites wonder, ‘Why do they have so much respect for the people who built these sites and then treat the indigenous people who live around them as inferior?'” he said.
With these DNA results, he added, they can now say, “Look, we’re related to the guys who built these pyramids. So stop being racist to us.”
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