The Amazon basin was a hotspot for the early cultivation of plants, with inhabitants having munched on squash and cassava more than 10,000 years ago, researchers have revealed.
The team say the new findings from Bolivia offer direct evidence such plants were grown in south-west Amazonia, meaning the region has a claim to join the Middle East, China, south-west Mexico and north-west South America as locations where wild plants were domesticated shortly after the last ice age. The team say the discovery chimes with other clues.
“[Previous work] identified south-west Amazonia as a potential centre of domestication because in this area they found a lot of wild relatives of domesticated plants,” said Dr Umberto Lombardo of the University of Bern, a co-author of the research.
Writing in the journal Nature, Lombardo and colleagues reveal how they made their discovery after investigating “forest islands” – raised, wooded areas, about 70 meters in diameter – within savanna in Llanos de Moxos, Bolivia.
Using a range of sources, including Google Earth, the team report more than 6,600 forest islands in Llanos de Moxos, adding that they looked at the makeup of soil samples at 82 of the sites, finding more than 60 showed telltale signs of human occupation – such as charcoal, shells and bone fragments. From these findings, the team estimated at least 4,700 of the “forest islands” identified were sites where humans once lived – and chucked their waste.
“They are places where people just threw their rubbish after eating or whatever they did,” said Lombardo, noting the accumulation went on for thousands of years, resulting in a raised platform that, safe from the savannah’s seasonal floods, eventually became colonised by trees.
Further analysis, using radiocarbon dating of charcoal or shell fragments within samples from 31 of the sites, reveal human occupation dating as far back as 10,850 years ago – shortly after the end of the last ice age, when cultivation of plants began independently in various regions of the world.
Lombardo and colleagues then examined tiny particles of silica that were found alongside the material for dating. These particles, called phytoliths, form in plant tissues with phytoliths from different types of plants, and sometimes even different species, showing particular shapes.
“Phytoliths are plant microfossils,” said Lombardo. “And we can use them to identify the plants that lived in that place in the past.”
The team report a heart-shaped phytolith that came from cassava at one site, in a sample dating to about 10,350 years ago, with scalloped, spherical phytoliths from the rind of squash plants found in samples dating as far back as 10,250 years ago.
Among other discoveries, the researchers found phytoliths from maize that date as far back as 6,850 years ago.
The team said the plants had probably been cultivated in home gardens. But whether the plants were domesticated there – a process involving selection of particular traits – or were already semi-domesticated is less clear.
Lombardo also cautioned that not all plants form phytoliths – among them are peanuts, which evidence from wild plants in the region suggests come from the south-west of the Amazon basin.
Dr Sarah Elliott, an environmental archaeologist from the University of Bournemouth, who was not involved in the research, said the study was significant, noting the team had found the oldest evidence for squash associated directly with human activity and the earliest maize cultivation in the Amazon basin.
“The human impact in the Amazon in the past was thought to be minimal,” she said. “But new research such as this study demonstrates that the nature of human occupation and alteration of the landscape is extensive, and this region now has evidence for the implementation of cultivation from as far back as 10,250 years [ago].”