Avocados are true superfoods: dense, buttery scoops of vitamins, fat and fiber, all in a hand-size package.
We worked for a long time to make them this way. According to a paper published Monday in the Proceedings of the National Academy of Sciences, people in what we today call Honduras made avocados a part of their diets at least 10,000 years ago and purposefully improved them starting more than 7,500 years ago — first by managing wild trees, and then by selectively planting new ones, to encourage thicker rinds and larger fruit.
This means fruit domestication at this site began thousands of years before the arrival of more commonly studied plants like maize.
“People were domesticating and cultivating their forests” long before they were planting crops in fields, said Amber VanDerwarker, a professor of anthropology at the University of California, Santa Barbara and an author of the paper.
Avocados first arose in central Mexico about 400,000 years ago. They were originally dispersed by megafauna: Giant ground sloths, elephantine gompotheres and burly toxodons all regularly gulped them down, choking-hazard-size pits and all. By the end of the Pleistocene epoch, around 13,000 years ago, megafauna had spread the oily fruits throughout Central and northern South America, and helped them diversify into at least three different species.
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But the mass megafaunal extinction that ended the Pleistocene left the avocados stranded: Without animals big enough to eat them whole and spread their seeds, their range began to shrink. At this point, “humans stepped in,” said Doug Kennett, a professor of environmental archaeology also at the University of California, Santa Barbara and an author of the paper. These humans — who, without the megafauna, now needed new food sources — began cultivating the fruit, “saving avocados,” Dr. Kennett said.
For the new study, researchers focused on a site in western Honduras called El Gigante, an elevated cave that people began frequenting 11,000 years ago. Over generations of living and working there, humans left heaps of discarded squash seeds, maize kernels, agave leaves and much more. Archaeologists have been sifting through it all for about 20 years.
To learn about how people at El Gigante enjoyed avocados, researchers looked at dozens of their seeds found in this “long-term trash pile,” as well as thousands of rind fragments, Dr. VanDerwarker said. They used radiocarbon dating to put these scraps in chronological order, and measured the thicknesses of the rinds and the dimensions of the seeds.
Comparing seed and rind sizes over time allowed the team to trace how humans shaped the fruit. Early on, people were “just picking wild fruits from their trees as they need to,” and the trash was littered with cherry-size seeds and thin bits of rind, Dr. VanDerwarker said.
In layers from about 7,500 years ago, the seeds had become larger and the rinds more robust. This suggests that people were managing existing trees, pruning some branches and new fruits in order to encourage the remaining ones to grow bigger.
In layers from 4,500 years ago, seeds had reached apricot size and rind thickness had pushed beyond the plant’s natural variation — “an indicator that people had started saving seeds and planting their own trees,” Dr. VanDerwarker said. The arborculturalists favored large fruits, as well as hefty skins that helped with preservation and transport.
The study gives “new evidence for 10,000 years plus, probably, of avocado use,” said Tom Dillehay, a research professor at Vanderbilt University who was not involved with this particular study. He said he had found similar signs of longstanding avocado enjoyment in northern Peru; other evidence has been found in Mexico, Colombia and Panama. Dr. Dillehay predicts that as research continues, more sites, and more types of manipulated food plants, will be discovered.
The finding also continues an ongoing shake-up of the notion that food domestication began with animals and cereal grains. That early avocado growers were putting so much effort into their plants is “different than what was imagined even 10 or 15 years ago,” Dr. Kennett said.
While our concepts of plant husbandry come and go, some things are more timeless. One reason to want to cultivate a thick avocado rind is for ease of scooping, said Dr. VanDerwarker, inspiring other tasty imaginings: “I think people have probably been eating guacamole now for a good 10,000 years.”