麻豆淫院

A recently published paper co-authored by CU Boulder鈥檚 Fernando Villanea offers new insights into what happened to the populations of Central Mexico a millennium ago

Between 1,100 and 900 years ago in modern-day Mexico, a series of droughts spurred on by global warming forced the nomadic hunter-gatherers of Aridoamerica to migrate south into the more verdant Mesoamerica, geographical home of the Aztecs and Mayans.听

Until recently, archaeologists assumed that, over time, these hunter-gatherers replaced their agricultural neighbors to the south. Yet that assumption was rooted solely in archaeological evidence, which, according to CU Boulder Assistant Professor of Archaeology Fernando Villanea, can be tricky to interpret.听听

鈥淭here鈥檚 always a problem when it comes to looking at archaeological remains, when you think there is a chance of two different groups of people going into each other,鈥� Villanea says.听

鈥淵ou find artifacts layered in time, and then you see them change, and you don鈥檛 really know what鈥檚 happening. You don鈥檛 know if these people are merging. You don鈥檛 know if one group is replacing the other. You don鈥檛 know if one group is learning from the other.鈥澨�

But a recently published paper co-authored by Villanea brings new evidence to bear on the question of who replaced whom in Central Mexico a thousand years ago鈥攐r whether anyone was replaced at all.听

听published May 12 in听Science, reveals that the genetic structure of people as far back as 1,400 years ago strongly resembles that of people living in Central Mexico today鈥攁 finding that all but disproves the population-replacement hypothesis.听

鈥淭he genetic results say that these two groups of people鈥欌�欌�攖he Aridoamericans and the Mesoamericans鈥斺�減robably just merged into each other,鈥� says Villanea.听

For the study, Villanea and his colleagues compared the DNA of people who lived along the Mesoamerican northern frontier before the onslaught of droughts with people who lived in the same area after the droughts.听

The DNA itself came from the subjects鈥� bones.听听

鈥淵our bone is living tissue, and it鈥檚 constantly repaired,鈥� Villanea explains. 鈥淎s you grow, you make more bone, and when you make that bone, a lot of cells get stuck between the bone layers. And it turns out, that is a perfect chemical condition to preserve DNA for a long time.鈥�

This preserved DNA taught Villanea and his colleagues that the genetic structure of the people of Central Mexico has had much greater continuity than once thought.听

But that鈥檚 not all it taught them. It also turned up two strands of previously unknown 鈥済host DNA,鈥� or DNA that can be found in ancient remains but not in people alive today.听

Ghost DNA is a common phenomenon, Villanea says, and when it shows up, there are two possible explanations.听

The first is that there are living people who share the ghost DNA but whose genes simply haven鈥檛 been sampled, and the other is that the original owners of the ghost DNA didn鈥檛 leave any descendants. Because scientists have made so much progress sampling DNA from all over the world, Villanea believes the latter explanation is likelier.

In the case of Villanea鈥檚 study, the two strands of ghost DNA, having never before emerged, add new layers of complexity to the demographic history of Central Mexico, which Villanea says is exciting.听

Yet what he finds perhaps even more exciting are not the study鈥檚 findings themselves but how the study was done.

鈥淭he real story is that this was a group of Mexican scientists who did all the ancient DNA sequencing in Mexico, in their own labs, and they were able to tell the story of the people of Mexico for themselves.鈥澨�听

Often, Villanea says, projects like this are done via 鈥渉elicopter research,鈥� whereby researchers from the Global North fly into lower-income countries, collect samples and return home to publish their findings, all without consulting local scientists or providing any benefit to local communities.听

Villanea and his colleagues took a different approach.

鈥淭his is the first time that we鈥檝e seen a major study come from a lab in a country outside the Global North,鈥� he says. That lab is the听International Laboratory for Human Genome Research at Universidad Aut贸noma de Mexico.听

Villanea adds that, for him, the research process was 鈥渁mazing.鈥�

鈥淥ut of the 27 authors, most of us are Latin American. All the email correspondence was in Spanish, which is something I鈥檝e never experienced before.鈥�

He smiles when he thinks about it. 鈥淚t鈥檚 a huge win for Mexico.鈥澨�

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