Some 9,000 years ago, corn as it is known today did not exist. Ancient peoples in southwestern Mexico encountered a wild grass called teosinte that offered ears smaller than a pinky finger with just a handful of stony kernels. But by stroke of genius or necessity, these Indigenous cultivators saw potential in the grain, adding it to their diets and putting it on a path to become a domesticated crop that now feeds billions.

Despite how vital corn, or maize, is to modern life, holes remain in the understanding of its journey through space and time. Now, a team co-led by Smithsonian researchers have used ancient DNA to fill in a few of those gaps.

A new study, which reveals details of corn’s 9,000-year history, is a prime example of the ways that basic research into ancient DNA can yield insights into human history that would otherwise be inaccessible, said co-lead author Logan Kistler, curator of archaeogenomics and archaeobotany at the Smithsonian’s National Museum of Natural History.

“Domestication—the evolution of wild plants over thousands of years into the crops that feed us today—is arguably the most significant process in human history, and maize is one of the most important crops currently grown on the planet,” Kistler said. “Understanding more about the evolutionary and cultural context of domestication can give us valuable information about this food we rely on so completely and its role in shaping civilization as we know it.”

In the Dec. 14 issue of the journal the Proceedings of the National Academy of Sciences, Kistler and an international team of collaborators report the fully sequenced genomes of three roughly 2,000-year-old cobs from the El Gigante rock shelter in Honduras. Analysis of the three genomes reveals that these millennia-old varieties of Central American corn had South American ancestry and adds a new chapter in an emerging complex story of corn’s domestication history.

“We show that humans were carrying maize from South America back towards the domestication center in Mexico,” Kistler said. “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.”

Humans first started selectively breeding corn’s wild ancestor teosinte around 9,000 years ago in Mexico, but partially domesticated varieties of the crop did not reach the rest of Central and South America for another 1,500 and 2,000 years, respectively.

For many years, conventional thinking among scholars had been that corn was first fully domesticated in Mexico and then spread elsewhere. However, after 5,000-year-old cobs found in Mexico turned out to only be partially domesticated, scholars began to reconsider whether this thinking captured the full story of corn’s domestication.

Then, in a landmark 2018 study led by Kistler, scientists used ancient DNA to show that while teosinte’s first steps toward domestication occurred in Mexico, the process had not yet been completed when people first began carrying it south to Central and South America. In each of these three regions, the process of domestication and crop improvement moved in parallel but at different speeds.

In an earlier effort to hone in on the details of this richer and more complex domestication story, a team of scientists including Kistler found that 4,300-year-old corn remnants from the Central American El Gigante rock shelter site had come from a fully domesticated and highly productive variety.

Surprised to find fully domesticated corn at El Gigante coexisting in a region not far from where partially domesticated corn had been discovered in Mexico, Kistler and project co-lead Douglas Kennett, an anthropologist at the University of California, Santa Barbara, teamed up to genetically determine where the El Gigante corn originated.