History

Chocolate gets its sweet history rewritten

Long believed to have been domesticated in Central America some 4,000 years ago, cacao has a more interesting story than previously thought. Friday, 2 November 2018

By Erin Blakemore

When did humans first start cultivating chocolate? It's not just a sweet conundrum: the question has long interested both biologists and anthropologists who wonder how and why cacao became so important to ancient Mesoamerican civilisations such as the Maya and Aztecs, both of whom cherished chocolate so much they used it in religious rites and as currency.

Archaeological evidence has pointed to the first use of cacao in Mesoamerica about 3,900 years ago. Traditionally, archaeologists have assumed that Mesoamericans were the first not just to use cacao, but to cultivate it.

Now, new research published in Communications Biology suggests that cacao was first domesticated around 3,600 years ago—and not in Mesoamerica.

In their hunt for the origins of domesticated cacao, researchers analysed the genomes of 200 cacao plants, then sussed out how each subspecies was related. As they worked, they looked for a telltale sign of domestication: genetic differentiation.

When a plant is domesticated, people select for desirable characteristics, breeding it over and over and correcting for things like size and taste. As a result, the genes of a domesticated plant don’t have as much variety as those of its wild relatives.

One likely candidate of early domestication was Criollo—the world’s most coveted variety of cacao—which was cultivated by the ancient Maya. The extremely rare variety of chocolate (it makes up just 5% of the world chocolate crop) is beloved by fans who love its deep and complex flavour, and students of cacao know that Criollo trees found in Central America are markedly different from the ones found in the Amazon basin. (Can GMOs save chocolate?)

“If we compare all the different [cocoa] populations, the only one that shows a very high amount of genetic differentiation consistent with an event of domestication is Criollo,” says Omar Cornejo, a Washington State University population geneticist who was the lead author on the study.

In this case, says Cornejo, early cacao cultivators seem to have bred Criollo from an ancient relative called Curaray. As they bred the plants generation after generation, its flavour shifted and its theobromine content—the compound that gives chocolate its bitterness and stimulant qualities—increased. Its susceptibility to disease rose as well, leading to its ever-increasing rarity.

According to Cornejo, cocoa domestication may have happened at any point between about 2,400 and 11,000 years ago, and the “most likely scenario” seems to be about 3,600 years ago. Surprisingly, Criollo was also found to have first been domesticated in South America (present-day Ecuador), not in Central America as previously thought.

But how did cacao get from the Amazon basin to Mesoamerica? Another newly released study gives a possible answer. Archaeologists have found the earliest example of cacao usage in the Americas on pieces of stone and ceramic from Mayo-Chinchipe sites in Ecuador that are about 5,300 years old—1,700 years earlier than the evidence from Mesoamerica. And since the Mayo-Chinchipe were in contact with groups along the Pacific coast, it seems likely that they traded cacao with people who brought it north to Mesoamerica.

Cacao “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,” said Michael Blake, co-author of the study, in a press release. It’s a new origin story for chocolate—and opens up sweet new opportunities for those who want to know more about how and when the substance was used in ancient times.

Erin Blakemore is a freelance science writer and author of 'The Heroine's Bookshelf." Follow Erin on Twitter.

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