Cave discovery of ancient avocados could rescue a global crop

The world’s appetite for avocados rests almost entirely on a single variety: the creamy Hass. That genetic sameness has streamlined production into a multibillion-dollar industry.

But it also invites disaster, as uniform orchards can collapse quickly when faced with a new pest, pathogen, or heat wave.

To find a different path, experts from Texas A&M University have traveled far back in time – 11,000 years – to a Honduran rockshelter whose charred ancient avocado pits chronicle the birth of the crop and offer clues to a more resilient future.

Avocado fossils in a cave

El Gigante, perched high in the western Honduran highlands, is a natural vault. Its dry interior has preserved plant remains that would normally rot in the humid tropics.

“It’s a truly incredible preservation of plant fossils and an abundance of avocado remains in a tropical region where plants generally do not preserve well,” said co-author Heather B. Thakar, an assistant professor in the Department of Anthropology at Texas A&M.

Layer upon layer of seeds, rinds, and other botanical scraps lie undisturbed, creating a sequential record of human meals – and human influence on local plants – stretching back to the end of the last ice age.

Avocados outlived their giants

According to the scientists, avocados first evolved to entice gigantic browsers such as gomphotheres and mammoths.

“Avocados are an amazing food source for humans, rich in healthy fats and nutrients that are essential to us,” Thakar said.

“But they originally evolved as a food source for ancient megafauna like giant sloths (gomphotheres) and mammoths that lived in the Americas during the last ice age.”

When those animals disappeared, humans stepped in to fill the ecological vacancy. Evidence at El Gigante shows early foragers selectively tending wild trees, nurturing seedlings with bigger seeds and fleshier fruit.

Farming over thousands of years

The team radiocarbon-dated hundreds of pits and rinds to build an exceptionally fine-grained timeline. Measurements revealed a steady upsizing: seeds grew larger and rinds thicker as the centuries passed.

“Through traditional forest management practices, people were selecting bigger and thicker-skinned avocados,” Thakar noted.

By 7,500 years ago, fruit size and durability hint that growers could harvest and transport avocados across larger distances. Full domestication appears roughly 2,000 years ago.

That makes avocado cultivation in Honduras older than maize, beans, or squash – crops that would later dominate Mesoamerican farming.

Past lessons for future crops

“Our work with El Gigante’s avocado remains offers valuable information about resilience and adaptation in the face of climate change,” Thakar said.

Unlike modern orchardists who propagate identical Hass cuttings through grafting, ancient farmers planted seeds, preserving genetic variety.

“Much of the genetic diversity of ancient avocados still exists in wild populations in Mexico and Central America,” Thakar added.

“By developing new avocado varieties through seed selection from both modern domesticated plants and wild populations, we may have a better chance of adapting to these changing conditions than relying on cloning alone.”

Broadening commercial stock with traits such as drought tolerance or disease resistance could buffer future harvests against environmental shocks.

Ancient avocado cave earns global notice

Scientists and local communities alike recognize El Gigante not just for its cultural importance, but for its scientific value as well.

Honduras has proposed the shelter for UNESCO World Heritage status, and Thakar’s team supplies documentation to bolster the case.

“All of the research that we have undertaken is used in support of El Gigante’s recent nomination as a UNESCO World Heritage site,” she said.

Although the site’s awkward three-meter climb has deterred looters, occasional campers and hunters do stray inside – making formal protection urgent.

A cave full of agriculture

El Gigante also stores early evidence for squash and maize domestication. Thakar is actively working on a publication that details the arrival of maize and the 4,500 years of diversification and improvement of this globally important crop.

Thakar’s methods – radiocarbon dating, stable-isotope chemistry, and 3-D morphometrics – merge hard science with cultural anthropology.

She applies this toolkit across Mexico, Belize, and Nicaragua to map humanity’s long partnership with plants.

Ancient farming, modern lessons

“The vast majority of food consumed today is a product of domestication,” Thakar said.

Understanding that protracted process can guide modern breeders. Ancient cultivators operated without greenhouses or genetic engineering, yet they produced crops – like avocadoes – exquisitely tuned to local soils and climates.

Unearthing those forgotten lineages may reveal alleles lost in today’s streamlined varieties.

“By studying domestication, we can recover ancient varieties and cultural knowledge that has helped humans become the incredibly successful species that we are,” said Thakar.

“It’s information that can be used to improve our crops today and ensure our continued survival into the future.”

From a Honduran cliffside to global orchards, the avocado’s story shows that agricultural resilience springs from diversity – and that sometimes the best way forward is to look back.

The study is published in the journal Proceedings of the National Academy of Sciences.

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