Avocados are known for their abundance of healthy nutrients and numerous health benefits.
Avocados surged in popularity with Millennials a decade ago, leading to criticism about overspending on avocado toast ‒ but a new study shows they were far from the first generation to love the luscious green fruit.
Carbon dating and analysis of a rock shelter in Honduras shows humans were eating avocados as long as 11,000 years ago, and began actively farming their trees as early as 7,500 years ago.
"This is really the best evidence we have for human-directed avocado evolution. It fills a big hole in our knowledge," said Dolores Piperno, a senior scientist emerita and curator of archaeobotany with the Smithsonian National Museum.
Scientists knew avocados had been an important part of diets in the Americans for thousands of years. This painstaking study of the remarkable archeology site in western Honduras showed just how far back the avocado - now a staple in American grocery stores - goes.
It also helps shift understanding around the beginnings of farming. The narrative in the Americas has often been that everyone was hunter-gatherers until corn appeared and then they became farmers.
But ethno-botanists and archeologists are finding the first agriculture actually began with trees, priming the peoples of Central and South America to later grow field crops like corn.
"These people literally domesticated their forests," said Amber VanDerwarker, an expert in ancient plants and agriculture at the University of California, Santa Barabara. She was the lead author on a paper published Monday in the Proceedings of the National Academy of Science.
When corn arrived "they already understood the whole notion of planting seeds and managing growth," she said.
The mysteries of a Honduran cave
The scientists researched a remarkable archeological deposit in the enormous El Gigante rock shelter found in western Honduras. More than 120 feet wide and 55 feet deep, it contains trash piles from the people who lived there that span the last 11,000 years. That included the fragments of more than 20,000 plants such as avocados, bottle gourds, agave, beans and squashes.
But the Honduran site is exceptional because of how long people lived there and its wealth of ancient kitchen leavings.
"These kinds of finds in archeology are incredibly rare and provide a window into the evolutionary history of plant domestication," said Douglas Kennett, a professor of environmental archeology at the University of California, Santa Barbara and the paper's senior author.
The El Gigante site was first excavated beginning in 1995. Scientists began radio carbon dating and a careful analysis of the contents in 2018. Seven years later they are publishing their meticulous work.
To do it, they assembled a collection of 1,725 avocado fossils that include rinds and pits showing changes in the shape and size of the fruits over time. Their rinds became thicker, the pits larger and the amount of the edible flesh greater.
Although avocado fossils have also been found in many of those places, the Honduran site is unique - it's the first proven site definitively showing the domestication of avocados.
"It's really the first evidence of a sequence that shows the initial exploitation, management and then human-selection of the trees leading to domestication," said Piperno.
It's possible that humans began farming avocado elsewhere earlier, but this is the only well-dated site, she said.
Making a better avocado took giant sloths and mastodons
A lot has gone into creating the millions of bowls of guacamole and plates of avocado toast Americans enjoy each year. It's a journey that involves mammoths and mastodons, human husbandry and, today, cloning.
About those mastodons. Humans, it turns out, were not the first beings to love - and change - avocados.
That honor goes to the megafauna that roamed the Americas until about 12,500 years ago. These included enormous animals such as mammoths, mastodons and giant sloths that could be 10 feet tall and weigh 2,200 pounds.
Avocados, it turns out, evolved to depend on these huge animals to disperse their seeds.
"Think about mammoths and mastodons. They were the only animals that could eat the fruit whole and pass the seed," said VanDerwarker.
Wild avocados originated in central Mexico. These massive animals spread them across Central and South America long before humans arrived.
But then the megafauna died off - around 12,500 years ago due to climate change and possibly overhunting by newly-arrived humans - leaving a role for farming.
"These plants were primed for this mutualistic kind of interaction, so humans stepped in," said Kennett.
The domestication of the avocado
When humans began living in the El Gigante rock shelter they were hunter gatherers. Over time they began to care for the rich fruit-bearing trees in the jungles around them. Those included avocados, palms and a tropical fruit called soursops.
The avocados they were eating were a type that first appeared in Guatemala, called guatemalensis. These are round variety with thick, warty skin. The Hass avocado, the most commonly eaten in the United States, is a cross between Mexican and Guatemalan avocado varieties.
The progression was first exploiting a food source, then managing it and then domesticating it.
"Within a couple of thousand years they were clearly managing their avocado trees," said VanDerwarker.
"We see the fruits getting larger and the rinds are getting thicker. They were doing things like selectively pruning branches, and thinning the fruits," she said. "When the trees first bud, you take off about half of them and that leads to larger fruit."
Then about 4,500 years ago the fossils show major increases inundefined
"This is the earliest documentation of avocado domestication," Kennett said.
The farmers also seemed to be selecting for thicker rinds which protect the fruit and make it easier to scoop the flesh out to eat.
Thicker rinds are important with avocados because they don't begin to ripen until they're picked from the tree. Thicker rinds also make them easier to store while they mature and become edible.
The fruit was independently domesticated at least three times in the Americas, but the findings in Honduras are the oldest example we have.
How did people 11,000 years ago eat avocados?
These early avocado eaters were probably eating them much the same as we might now. "It would have been just picking the fruit, splitting it open and scooping it out," said Kennett.
Guacamole isn't inconceivable.
"Chili peppers go back to about the same time period," he said.
Chips, however, would have taken a little longer.
Maize (corn) wasn't domesticated until at least 9,000 years ago. It didn't reach this general area until at least 6,000 years ago, based on available data.
The first corn found in the El Gigante rock shelter dates to about 4,200 years ago, he said.
A new love affair with an old fruit
While the people living at the El Gigante site might have been taken aback by todays' large, fleshy avocados, they wouldn't be surprised that Americans love them so much. In fact, the question might instead have been, "What took you so long?"
Back in the 1980s, avocados were rare in U.S. supermarkets. Not until the 1990s, when the California Avocado Commission launched a public relations effort to teach people how to eat them and tell when they were ripe, did sales begin to spike.
Since 2000, U.S. per capita consumption of the fruits' buttery interior has gone from just under two pounds to almost nine pounds per person.
Today, 90% of the avocado industry is dominated by just one variety, the Hass avocado with its black, pebbly rind. These trees are all clones from the original Hass tree developed by Rudolph Hass, a postman in Los Angeles.
While avocados are grown in California and Florida, the vast majority of those we consume today come from Mexico - more than 90%.
So much so that avocados are now the highest value agricultural commodity imported into the United States, having surpassed bananas in 2017.
"The increase in consumption is unbelievable, it's amazing how it's been assimilated," said Luis Ribera, an agricultural economist with Texas A&M University. "They've become a grocery store staple."