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Halloween is tomorrow, and there will be hordes of children (and adults) stuffing their faces with chocolate of all kinds all over the place—a reminder that humans have a pretty personal relationship with this delightfully sweet candy. And now it looks like that relationship started further back then we imagined. New evidence reported in Nature Ecology & Evolution on Monday suggests that the cacao tree, from which we collect cocoa beans to make chocolate, was domesticated by humans in South America more than 1,500 years earlier than previously thought. This would push back cocoa bean domestication to 5,400 years ago, making this new discovery the oldest archeological evidence of domesticated cacao in the world, and would also peg the origin point of cocoa production to the upper Amazon of South America, not Central America as was once thought.

The new findings paint a more complicated and deeper picture of humans’ relationship with cacao, one of the world’s biggest economic crops to date. “The story of cacao is a rich story, of the history of a plant that in its domestic form is a gift to the world from the people who transformed it through generations of labor and careful tending,” says Michael Blake, an anthropologist at the University of British Columbia in Vancouver and a coauthor of the new study. “This story can be repeated with an almost endless list of foods and materials that the world takes for granted today, but whose origins we seldom know much about and rarely appreciate.”

Cacao probably wasn’t used by those old civilizations to make edible chocolate, but tests show the indigenous populations living in the Amazon all those years ago were definitely using the cacao seed, part of the greater pod used to make chocolate itself. Spanish explorers arriving in Central America in the late 15th century found native people using cacao to make hold and cold beverages, drying and roasting and grinding the seeds into a paste to extract out the active ingredients like caffeine. By the next century, Spain and other countries were importing troves of cacao into the European continent.

Indigenous people in the Amazon today still use cacao to make fermented drinks. Yet the spread of cacao through the Americas has always been a mystery for anthropologists and plant scientists alike. Previous investigations have confirmed the cacao tree is most genetically diverse in equatorial South America.

Blake and his team his team sought to reconcile that fact with what the archeological evidence was saying, and they got lucky. The new discovery hinges on the analysis of ceramic artifacts found in the Santa Ana-La Florida archeological site in present-day Ecuador, home to some of the earliest signs of the Mayo-Chinchipe culture that lived in the area nearly 5,450 years ago. Blake and his team thought the artifacts may have been used as vessels for cocoa drinks, but nobody had ever looked into it.

The team used three lines of testing to characterize the artifacts and find evidence of cacao domestication: the presence of theobromine (a major compound in domestic cacao but not in its wild relatives, which creates similar effects to caffeine); the presence of preserved particles of starch from cacao trees; and the positive identification of old DNA fragments specific to cacao. There’s enough theobromine and ancient DNA in the samples to show cacao presence wasn’t incidental, but part of routine customs. One of the artifacts testing positive for cacao was dated to between 5,310 and 5,440 years old. “All these facts tend to demonstrate that cacao was really domesticated and used in their everyday life by Mayo Chinchipe people and not simply used opportunistically,” says Claire Lanaud, a researcher at the French Agricultural Research Centre for International Development and a coauthor of the study.

According to the genetic profiles of the samples in Ecuador, people in the upper Amazon were harvesting varieties of cacao similar to ones later grown in Mexico, suggesting the use of cacao spread northwards into other parts of South America and later into Central America and southern regions in Mexico. The findings also seem to confirm an older history of cacao, supported by theobromine found in 3,100-year-old artifacts found farther south in Honduras and 3,900-year-old artifacts found on the Pacific Coast in Mexico.

Cameron McNeil, a researcher at Lehman College in New York who was not involved in the study, doesn’t think the new findings are particularly surprising, but she does find them interesting for “turning back the date of cacao use by more than a thousand years, and that they demonstrate that South Americans were using the seeds as well as the pulp. Many scholars have proposed that it was the people of lower Central America, or Mesoamerica, who first used the seeds in beverages.”

Juan Carlos Motamayor, an agricultural engineer at Universal Genetic Solutions who has previously studied cacao domestication through genetic analysis and was not involved with the study, believes the results “provide convincing evidence” that early use of cacao occurred in Ecuador. “This is extremely interesting,” he says, “because it would support the hypothesis that trading and knowledge of the cocoa bean was possible at the time to facilitate the movement to Mesoamerica where it was intensively domesticated.”

However, it’s important to recognize evidence of usage does not necessarily equate to evidence of outright domestication of cacao. “For example,” says Motamayor, “if we find residues of lingonberries in ancient pottery from Native Americans of the Pacific Northwest, does that mean that this fruit was domesticated by them? Lingonberry is still an undomesticated fruit.”

Motamayor thinks the genetic analysis used in this study to determine ancestry for the trees was a bit limited, and he hopes to see a deeper sequencing that could better verify the genetic origins of the samples found. He also notes that domestication usually means breeding a few varieties of a plant with traits of interest, bred intensively to generate crops. Over time, this creates a very unique genetic signature that differs from wild populations of the same plant. “We only find genetic evidence of this process in Criollo populations, with none of the other populations showing a similar signature,” he says. “Furthermore, the only clear trait in cacao related to domestication is self-compatibility, the ability of the trees to self-reproduce.” His group has studied this trait in over 5,000 samples of cacao, and he says they’ve yet to find genetic signs of self-compatibility from cacao plants in the upper Amazon region, which would suggest domestication probably occurred using plants located in outlier populations, away from the epicenter of cacao diversity. Further work is necessary to find other evidence that could support [the notion of] active domestication in South America.”

Blake acknowledges this limitation, and his team hopes to incorporate greater genetic analysis as a part of their follow-up investigations into other collections of excavated pottery. “It is very exciting for archaeologists, anthropologists, and historians to find the actual evidence of ancient activities and practices that help us fill in the gaps in our knowledge, more fully tracing the details of our human past,” he says. And as we cram our faces with chocolate treats this Halloween, we can take comfort in the knowledge that our species’ love of the stuff extends far back into our history.

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