(CN) — New archaeological research directly ties a signature American crop to the story of how ancient human populations grew and spread over time.
By studying the genome of maize crops, researchers have discovered new details about how maize moved between Central and South America thousands of years ago.
Maize was first cultivated in southwestern Mexico some 9,000 years ago, derived from an annual grass called teosinte. As domestication continued, it spread into South America around 2,000 years later.
In a new study, researchers confirm that maize crops were then reintroduced to Central America, providing an important source of genetic diversity as maize firmed up its role as a vital American crop.
The findings, published on Monday in the Proceedings of the National Academy of Sciences, add a layer of complexity to scientists’ understanding about corn domestication and its role in shaping ancient civilizations.
Archaeologists sequenced the DNA of three maize cobs, each around 2,000 years old, found in the El Gigante rock shelter in Honduras. Analysis of the cobs’ genomes showed that the Central American crops have South American ancestry.
Logan Kistler is the curator of archaeogenomics and archaeobotany at the Smithsonian’s National Museum of Natural History. He co-led the study.
Kistler explained why bringing maize back to Mexico may have made for better crops.
“We show that humans were carrying maize from South America back towards the domestication center in Mexico,” Kistler said in comments released with the research.
“This would have provided an infusion of genetic diversity that may have added resilience or increased productivity. It also underscores that the process of domestication and crop improvement doesn’t just travel in a straight line.”
Researchers compared the ancient maize DNA with that of previously studied varieties, coming from cobs and seeds. The genetic link between maize crops was subtle, but consistent, researchers said. After repeating the genetic analysis with several different methods, the result was the same.
Kistler’s team had previously studied millennia-old maize cobs from sites in Central America. After being surprised to find both partially and fully domesticated maize varieties in regions near each other, the researchers set out to better understand the story of maize cultivation.
At El Gigante, researchers have uncovered more than 10,000 maize remains, from whole cobs to just fragments, like stalks and leaves. Radiocarbon dating has proven that some samples are as old as 4,300 years.
Not all ancient cobs are equal, and only a few samples proved suitable for full genomic analysis; out of 30 samples, only three worked in the study. They date back between 2,300 and 1,900 years.
Still, the shape and structure of the maize cobs studied are similar to those from 4,000 years ago, so the elder cobs may have been equally productive, researchers say. It may be that reintroducing crops from South America is just what gave ancient maize the boost it needed to become a primary component in the diet of people living in ancient Central America.
In fact given the timing, researchers hypothesize that ancient corn — a crop that today feeds billions of people — in early agricultural communities in Mesoamerica eventually gave way to civilizations like the Olmec, Maya, Teotihuacan and Aztec.
Kistler called crop domestication “arguably the most significant process in human history, and maize is one of the most important crops currently grown on the planet.”
“We can’t wait to dig into the details of what exactly happened around the 4,000-year mark,” Kistler said. “There are so many archaeological samples of maize which haven’t been analyzed genetically. If we started testing more of these samples, we could start to answer these lingering questions about how important this reintroduction of South American varieties was.”