An international team of scientists has found that the upper Amazon region gave birth to the domesticated Theobroma cacao, the plant from which chocolate is made.

Theobroma cacao was a culturally important crop in pre-Columbian Mesoamerica, a historical region and cultural area in North America that extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica.

Cacao beans were used both as currency and to make the chocolate drinks consumed during feasts and rituals.

Archaeological evidence of cacao’s use, dating back to 3,900 years ago, previously planted the idea that the cacao tree was first domesticated in Central America.

However, genomic research shows that the cacao’s greatest diversity is in the upper Amazon region of northwest South America, pointing to this region as its center of origin.

“Our study shows us that people in the upper reaches of the Amazon basin, extending up into the foothills of the Andes in southeastern Ecuador, were harvesting and consuming cacao that appears to be a close relative of the type of cacao later used in Mexico — and they were doing this 1,500 years earlier,” said University of British Columbia’s Professor Michael Blake, corresponding author of the study.

“They were also doing so using elaborate pottery that pre-dates the pottery found in Central America and Mexico.”

“This suggests that the use of cacao, probably as a drink, was something that caught on and very likely spread northwards by farmers growing cacao in what is now Colombia and eventually Panama and other parts of Central America and southern Mexico.”

For the study, Professor Blake and co-authors studied ceramic artifacts from Santa Ana-La Florida, in Ecuador, the earliest known site of Mayo-Chinchipe culture, which was occupied from at least 5,450 years ago.

They used three lines of evidence to show that the Mayo-Chinchipe culture used cacao between 5,300 and 2,100 years ago:

(i) presence of starch grains specific to the cacao tree inside ceramic vessels and broken pieces of pottery;

(ii) residues of theobromine, a bitter alkaloid found in the cacao tree but not its wild relatives;

(iii) fragments of ancient DNA with sequences unique to the cacao tree.

“Evidence of cacao use was found by analyzing the starch grains characteristic of the genus Theobroma, traces of theobromine, a biochemical compound specific to mature cacao beans, and ancient cacao DNA found in ceramic vessels, some of which dated back more than 5,300 years,” said co-author Dr. Claire Lanaud, a researcher at CIRAD, France.

The findings suggest that the Mayo-Chinchipe people domesticated the cacao tree at least 1,500 years before the crop was used in Central America.

As some of the artifacts from Santa Ana-La Florida have links to the Pacific coast, the researchers suggest that trade of goods, including culturally important plants, could have started cacao’s voyage north.

“For the first time, three independent lines of archaeological evidence have documented the presence of ancient cacao in the Americas: starch grains, chemical biomarkers, and ancient DNA sequences,” said first author Dr. Sonia Zarrillo, from the University of Calgary.

“These three methods combine to definitively identify a plant that is otherwise notoriously difficult to trace in the archaeological record because seeds and other parts quickly degrade in moist and warm tropical environments.”

The study appears in the journal Nature Ecology & Evolution.

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Sonia Zarrillo et al. The use and domestication of Theobroma cacao during the mid-Holocene in the upper Amazon. Nature Ecology & Evolution, published online October 29, 2018; doi: 10.1038/s41559-018-0697-x