The tropics are a paradise for all but a skeleton. Humidity keeps rainforests green but does little to preserve bodies, leading to a shortage of ancient skeletal remains in neotropical regions like Central America.
But deep in the jungles of Belize, beneath the dry shelter of two rock shelters, the skeletons of people who died as much as 9,600 years ago are exceptionally well preserved. Their bones provide a rare glimpse into the region’s ancient genetic history, which is largely unknown.
A group of scientists has now extracted the DNA of these ancient people, providing new insight into the genetic history of humans in the Maya region. The article was published Tuesday in the journal Nature Communications. More than 5,600 years ago, the researchers identified a previously unknown mass migration from the south that preceded the arrival of intensive corn cultivation in the region. This migration of people, who are most closely related to today’s speakers of the Chibchan languages, contributed more than 50 percent to the ancestry of today’s Mayan-speaking peoples.
Lisa Lucero, an anthropologist at the University of Illinois at Urbana-Champaign who specializes in the ancestral Maya and was not involved in the research, said the new results “have the potential to revise and modify the early history of the First Americans.” rewrite.”
Xavier Roca-Rada, a doctoral student at the University of Adelaide, said the results “fill a gap between the oldest previously studied individuals from the Maya region and the time before the settlement of Mesoamerica.”
The new paper emerged from ongoing excavations led by authors Keith Prufer, an environmental archaeologist at the University of New Mexico, and Douglas Kennett, an archaeologist at the University of California, Santa Barbara. The researchers excavated two rock shelters in the Bladen Nature Reserve, a remote and protected area of Belize that kept the sites, which were used as burial grounds, undisturbed for thousands of years. “People just kept coming back to them over and over and burying the dead,” said Dr. prufer.
The shelters were also inhabited by the living, who made tools and cooked, evidenced by the buried bones of armadillos, deer and a type of rodent called a paca, said Dr. prufer. The bottom of the excavated pit contained a piece of a giant sloth, which may even predate the human occupation of the shelter, he said.
The excavations also uncovered a secret, formerly slimy protective layer under the ground. About 5,000 to 6,000 years ago, before the Classical Period of the Maya, humans harvested tiny Pachychilus snails for food. “They would cook them and chop off the end of the shell and eat the meat out,” said Dr. prufer. Whoever inhabited these shelters feasted on these snails, and their discarded shells protected the bodies buried beneath them. “This layer of slag actually protected the lower tombs from the Maya who dug through it,” he said.
dr. Kennett and Dr. Prufer studies these early graves to understand how the region moved from hunting and gathering to developing intensive agriculture of maize, chili peppers, and manioc (also known as cassava). In a 2020 paper, they described evidence of corn consumption in the bones of individuals who lived 4,000 to 4,700 years ago.
David Reich, a geneticist at Harvard Medical School, led the extraction of ancient DNA from 20 individuals buried in the shelters over the course of 6,000 years. The analysis revealed several human migrations to the Maya region, in what is now southeastern Mexico and northern Central America.
They found three distinct groups: one that lived 7,300 to 9,600 years ago, another that lived between 3,700 and 5,600 years ago, and a third group of modern Maya. The first group appears to be genetically linked to a southward migration across the Americas during the Pleistocene. But the second group was genetically related to the ancestors of Chibchan speakers who lived further south.
The authors hypothesize that this population shift was the result of massive migration from the south. “That was the spectacular result,” said Dr. Kennett.
The finding rejects an old assumption that agricultural technology spread across America through the spread of crops and practices — the spread of knowledge as opposed to the spread of people, said Dr. Reich. The new results suggest that this migration was critical to the spread of agriculture, such as a scenario where Chibchan speakers migrated north with varieties of maize, which they then grew and distributed in local populations, the authors write.
“People came to the region from the south, with these domesticated plants and also the knowledge systems on how to grow them,” said Dr. Kennett.
David Mora-Marín, a linguistic anthropologist at the University of North Carolina at Chapel Hill and an author of the paper, conducted an analysis of early Chibchan and Maya languages. He found that a term for maize had spread from the Chibchan language into the Mayan languages, further supporting the idea of a Chibchan origin of maize.
The field of ancient DNA has been criticized for a lack of ethics or appropriate involvement in communities that may have descended from the ancient humans being studied.
dr. Kennett and Dr. Prufer conducted their archaeological research with the Ya’axché Conservation Trust, a Belizean non-governmental organization largely staffed by descendants of Mayan communities. The researchers consulted with these communities, presented research results and, at the request of the local population, translated summaries of findings into the languages Mopan and Q’eqchi’. In the discussions, the communities expressed a desire to learn more about the diets and precolonial family units of the ancient people who lived in the cave. Because of these conversations, the authors have placed greater emphasis on these topics in the paper, said Dr. Kennett.
Krystal Tsosie, a genetics researcher at Vanderbilt University, said she wanted to see a more detailed description of how community feedback influenced the article. dr. Tsosie added: “The process of proper engagement also means that community members are credited appropriately and transparently for informing and enriching the research.”
Ripan Malhi, a genetic anthropologist at the University of Illinois at Urbana-Champaign, noted that the authors uploaded the ancient DNA data to a public database “without warranties or restrictions on use indicated.” Ancient DNA can provide a shortcut to the DNA of modern communities without their permission. “This could have implications for the current Maya in the region,” he said.
dr. Lucero and Mr. Roca-Rada said more data was needed to prove the researchers’ hypothesis that a southern migration had brought corn to the Maya region. for dr. Lucero, the question is whether researchers should acquire that data. “Should we dig up ancestors?” he asked. “Would we want someone to dig up ours to answer interesting but non-vital research questions?”
dr. Kennett and Dr. Prufer last visited Belize in January 2020 to present the preliminary results of the new article to Mayan communities. The pandemic has since banned the return of the researchers, but Dr. Prufer said they hoped to return this summer to continue excavating and “keep on our promise to return every year we work and keep everyone informed.”
