A team of scientists led by researchers with the Smithsonian's National Museum of Natural History and Texas A&M University recently uncovered genetic traces of ancient migration in DNA from avocados growing in Nicaragua. They found evidence that, around 5,000 years ago, people migrating north from South America carried the oversized seeds of one of their favorite fruits—avocados. As these seeds were dispersed throughout the humid lowlands of Central America, they hybridized with native varieties, producing a diversity of avocado varieties that produce the large, smooth-skinned berries that are now enjoyed around Central America. Despite resembling the avocados found in humid regions like Florida and the Caribbean, these local varieties are genetically distinct from the commercially grown fruits found in guacamole.
In a paper published today, July 22, in the journal Plants, People, Planet , a team led by archaeobotanist Kevin Wann, who conducted the research as a fellow at the museum, examined DNA from avocado leaves collected in Nicaragua, Honduras and southern Mexico. They also spoke with the farmers and gardeners to learn how they cultivate these local avocados.
"There is a much wider breadth of avocado diversity that science had not yet documented," said Wann, who is now pursuing his doctorate in the Department of Anthropology in the College of Arts and Sciences at Texas A&M and had never eaten an avocado before this project. "We could potentially tap into this genetic diversity to conserve commercial avocado plants that are vulnerable to disease."
A Crop of Clones
The natural range of avocado trees (Persea americana) extends from Mexico to Peru. For more than 10,000 years, humans in this area have coveted the plant's fruit, whose yellowish-green flesh is packed with nutrients and fats. These superfoods are now cultivated around the world— in 2024, growers produced more than 11 million metric tons of avocados .
More than 80% of these avocados were a single variety known as the Hass avocado. These large, long-lasting avocados are produced through clonal grafting, where a branch is taken off one Hass avocado tree and attached to another tree to bear the same exact fruit. As a result, most avocados in grocery stores are genetically indistinguishable. This makes all Hass avocados vulnerable to the same threats. A single disease or change in temperature or precipitation can wipe out an entire population of Hass avocados.
Increasing the genetic diversity of avocados is crucial to protecting this multi-billion-dollar industry. According to Wann, the muggy lowlands of countries like Nicaragua and Honduras are rich in avocado diversity. Here, traditional agricultural practices have honed the region's native avocado varieties, also known as landraces, for thousands of years.
A Hotbed of Avocado Diversity
To document the diversity of avocado landraces in Central America, Wann and his colleagues collected leaf samples from dozens of varieties in southern Mexico, Nicaragua and coastal Honduras. During the field work in southern Mexico, Wann dealt with bouts of food poisoning and was stung in the face by a wasp while collecting samples from a roadside grove of avocado trees.
The researchers also interviewed local gardeners and rural farmers in Nicaragua and Honduras to learn more about native avocado varieties. This agricultural perspective was crucial according to Logan Kistler, the museum's curator of archaeobotany and archaeogenomics who advised Wann during his fellowship and was the senior author of the new paper.
"You can't think about biodiversity without considering agriculture, because it's one of the most impactful ecological activities we do," Kistler said. "Traditional agricultural practices have shaped these plants for thousands of years."
During a tour of one grove in Nicaragua, a farmer offered Wann an avocado, unaware that the scientist had never tasted the fruit he studied.
"I wanted to see how far I could go into my dissertation studying avocados without ever eating one," he said. "I made it four years but when one of the native farmers offered me one, I couldn't turn him down.
"And it was delicious," adds Wann, who now routinely enjoys guacamole.
The locals shared valuable insights with the researchers. They confirmed that these lowland avocado landraces had not experienced root rot, the most common disease affecting commercial avocados. Some Nicaraguan farmers even graft commercial avocado branches onto native avocado trees, which are better adapted to the local environment.
Ancient Genetic Clues
In the lab, the team extracted and analyzed DNA from the harvested leaf samples. In total, the team collected DNA from 47 native avocado landraces (32 of which came from Nicaragua). The scientists compared the DNA from the various landraces with previously published genetic data from more than 200 other avocado lineages.
The team discovered that the avocado samples collected in southern Mexico were closely related to ancestral highland populations found in other parts of Mexico as well as commercial varieties. In contrast, the landraces sampled in the lowlands of Nicaragua were genetically tied to avocados found further south, including populations along the coast of Colombia.
This revealed that many local landraces in this part of Central America are planted from fruits originally grown in South America. The team posits that human populations brought their local avocado varieties with them as they migrated through the Americas. Based on the genetics, this avocado relocation likely occurred around 5,000 years ago, which is roughly when other South American crops, like chocolate and certain varieties of maize, appear in the Central American archaeological record.
Kistler thinks varieties of this fleshy fruit continued to move back and forth as ancient communities migrated over thousands of years.
"It was a very connected landscape throughout Central and South America," Kistler said. "It's not one big episode of people moving avocados and other food species around, it's a constant interchange."
The Fruit's Future
Wann thinks the trove of avocado diversity preserved in Central America's lowlands could help protect commercial avocados from the fate of other clonal crops like bananas, which have been devastated by fungal pathogens in the past. The region's local landraces are also adapted to warmer and wetter climates.
However, some of these local avocado varieties are at risk. Wann and his colleagues heard that several Nicaraguan farmers have cut down some of their local avocado trees to make more space for commercial varieties. Decreasing this ancient avocado diversity could threaten the fruit's future.
"These locally grown fruit trees are vital to the longevity of avocados as a species," Wann said. "Their high levels of genetic diversity makes them more prepared to face potential shifts in climate or diseases compared to the ones you'd buy at a supermarket."
In addition to Wann and Kistler, the study included authors affiliated with the University of Oklahoma and California State University Long Beach. This research was supported by the Wenner-Gren Society.
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