Tracing the origins of chocolate: A recent study is shedding new light on the domestication and spread of the cocoa bean. | The Past

Mesoamerica is often considered the ‘homeland’ of chocolate due to its significance for many ancient cultures in this region, but the cocoa tree, Theobroma cacao, in fact originated in the tropical rainforests of South America. Until now, though, our understanding of the plant’s early use – and how and when it spread to other parts of the Americas – has been limited.

The recent research project used a combination of archaeogenomics (the study of ancient DNA) and biochemical analysis to investigate the history of cacao’s domestication and cultivation. The team sampled 352 pots from archaeological sites across Peru, Colombia, Ecuador, Mexico, Belize, and Panama, representing 19 ancient cultures spanning five millennia, from 5,900 to 400 years ago. The researchers analysed residues left behind by the contents of the pots, looking for the ancient DNA (aDNA) of T. cacao. They carried out methylxanthine analysis of the same artefacts, as well: T. cacao seeds contain three methylxanthines – theobromine, caffeine, and theophylline – so high levels of these substances could also indicate the presence of chocolate. Additionally, the study took advantage of a recent genetic resequencing of a collection of modern cacao trees representing the current global diversity of the species. The team used this data to explore the genetic relatedness of varieties of cacao consumed in the past (as found in the ceramic residues) and modern tree populations originating from various locations, which offered further insight into the origins of historic cacao varieties and the pathways of their ancient domestication.

Using this multi-pronged approach, researchers were able to determine that the cacao tree was domesticated in the rainforests of the Upper Amazon basin at least 5,300 years ago, and that it first began spreading to other regions across South and Central America at around the same time. The analysis revealed just how extensive the use of cacao was in the regions examined: T. cacao aDNA was present on almost 30% of the ceramics tested, used in both domestic and ritual activities. Furthermore, evidence of early chocolate consumption was found in several cultures where it was not previously known, including – for the first time – widespread use in areas of South America outside the plant’s native area of origin.

Of interest, too, were the ways in which different strains of the cocoa plant developed. The diversity present in modern populations of T. cacao emerged as a result of millennia of both environmental changes and human interaction. As we see with other domesticated plants throughout history, ancient farmers in South America quickly began to transport the cacao bean away from its place of origin – and out of its natural range – through either human migration or trade, in the process selecting the varieties with preferred traits, which ultimately led to the development of a multitude of geographically disparate varieties. By analysing the DNA of ancient and modern varieties the researchers were able to identify genetic mixing between cacao trees from distant populations occurring as early as the Middle Holocene (4,000-6000 years ago) in South America.

These findings not only tell us more about the spread of the cocoa plant but also offer fresh insights into ancient connections between communities in different regions. In particular, we now have new information about cultural links between peoples in the Amazon and those on the Pacific coast of the continent during the earliest stages of agriculture, with evidence that cacao was playing a prominent role in these interactions. We have a better understanding as well of chocolate’s spread from the South American Amazon into Central America, although whether this occurred northward over land or by sea along the Pacific coast remains a question to be answered.

This study highlights the complex early history of cacao domestication and draws attention to the plant’s importance in far-reaching trade and exchange patterns that started more than 5,000 years ago. The results offer valuable insight into the early development and spread of a plant that had great significance for many ancient cultures and remains hugely popular today. It is also hoped that an improved understanding of Theobroma cacao’s genetic history could help us manage cacao tree resources better in the future. The research has been published in Scientific Reports (https://doi.org/10.1038/s41598-024-53010-6).

Text: Amy Brunskill / Images: Pexels – Tope A Asokere; Claire Lanaud