That cultivation eventually altered entire regions of the Amazon, the study argues. Levis and her colleagues found that some of these species domesticated by indigenous people—including the brazil nut, the rubber tree, the maripa palm, and the cocoa tree—still dominate vast swaths of the forest, especially in the southwest section of the Amazon basin.

“Modern tree communities in Amazonia are structured to an important extent by a long history of plant domestication by Amazonian peoples,” says the paper.

Other cultivars remain successful, but they were so thoroughly changed by agriculture that they are no longer found in the forest at large. Peach palm, Bactris gasipaes, was domesticated to have fruits as large as 200 grams. In the wild, its fruits originally had a mass of only one gram. It still appears in gardens and small farms across South and Central America today.

The ancient farmers and gardeners of the Amazon would likely have been speakers of languages from the Arawakan and Tupí families. They would probably have lived in “galactic” communities—groups of settlements separated by distance but linked by trade and communication—along the banks of the rivers that cross and irrigate the forest.

“Recent archaeological studies, especially in the last two decades, show that indigenous populations in the past were more numerous, more complex, and had a greater impact on the largest and most biodiverse tropical forest in the world,” said José Iriarte, an archeologist at the University of Exeter who was not connected to the study, in an email.

“This is the largest and more comprehensive study” to reveal that influence so far, he added. “It is is very sound, since it not only includes archaeologists (which have been stressing the larger role played by humans in shaping Amazonian forests), but also botanists and soil scientists, among other ‘hard scientists.’”

Eglee Zent

The paper brings together more than 80 years of research into both the ecology of the Amazon and the indigenous people who lived there. It collates data from two sources: the Amazon Tree Diversity Network, a long-running index of the animal and plant species who inhabit the rainforest; and a database of the archeological sites excavated around the Amazon.

These archeological sites include anything that suggests human influence: ceramics, earthworks, rock paintings, and mounds of dirt. It can also include anthropogenic soils, or “Amazonian dark earth,” a black mixture of charcoal and organic material that resulted from ancient Amerindian slash-and-char techniques.

Because it collates two different data sources, the paper also suggests areas of future research. It finds that certain areas of the Amazon are home to the types of tree species that indicate ancient human influence, but that these places have not yet been explored or excavated by academic researchers. “This tells archaeologists where to do new projects,” says Ariarte.