Climate change caused major declines in early South American populations

New research from University College London (UCL) has revealed that abrupt climate change drastically reduced early South American populations. The study is the first to demonstrate the magnitude of these population declines, which took place between 6,000 and 8,000 years ago.

“Archaeologists working in South America have broadly known that some 8,200 years ago, inhabited sites in various places across the continent were suddenly abandoned. In our study we wanted to connect the dots between disparate records that span the Northern Andes, through the Amazon, to the southern tip of Patagonia and all areas in between,” said study lead author Dr. Philip Riris of the UCL Institute of Archaeology.

“Unpredictable levels of rainfall, particularly in the tropics, appear to have had a negative impact on pre-Columbian populations until 6,000 years ago, after which recovery is evident. This recovery appears to correlate with cultural practices surrounding tropical plant management and early crop cultivation, possibly acting as buffers when wild resources were less predictable.”

The researchers focused on the climate during the transition to the Middle Holocene, which began 8,200 ago. The Middle Holocene was characterized by major cultural changes. For example, hunter-gatherers started experimenting with different domestic plants at this time.

Despite the widespread population declines that were identified in the study, the researchers found that indigenous people of South America were thriving before and after the middle Holocene.

“In the years leading up to population decline, we can see that population sizes were unharmed. This would suggest that early Holocene populations, probably with a social memory of abrupt climate change during the Pleistocene-Holocene transition, developed successful strategies to deal with climate change,” said study co-author Dr. Manuel Arroyo-Kalin.

“Abandonment of certain regions and the need to adapt quickly to new circumstances may have promoted the exploration of alternative strategies and new forms of subsistence, including the early adoption of low scale cultivation of domestic plants. Viewed in the context of at least 14,000 years of human presence in South America, the events of the Middle Holocene are a key part of indigenous South Americans’ cultural resilience to abrupt and unexpected change.”

The team compared thousands of radiocarbon dates from 1,400 sites to investigate how the populations changed over time, and then compared this information with climate data.

“We studied ancient records of rainfall such as marine sediments for evidence of exceptional climate events,” said Dr. Riris. “Within windows of 100 years, we compared the Middle Holocene to the prevalent patterns before and after 8,200 years ago. Normal patterns of rainfall suggest on average an unusually dry or wet year every 16-20 years, while under highly variable conditions this increases to every 5 years or so. This puts in perspective the challenge that indigenous communities would have faced.”

The researchers believe that the findings provide an important historical context for understanding how ancient indigenous South American populations handled climate change.

“Our study brings a demographic dimension to bear on understandings of the effects of past climate change, and the challenges that were faced by indigenous South Americans in different places,” said Dr. Arroyo-Kalin. “This understanding gauges the resilience of past small-scale productive systems and can potentially help shape future strategies for communities in the present.”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer

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