Did pre-Columbian populations of the Amazonian biome reach carrying capacity during the Late Holocene?

The increasingly better-known archaeological record of the Amazon basin, the Orinoco basin, and the Guianas both questions the long-standing premise of a pristine tropical rainforest environment and also provides evidence for major biome-scale cultural and technological transitions prior to European colonisation. Associated changes in pre-Columbian human population size and density, however, are poorly known and often estimated on the basis of unreliable assumptions and guesswork. Drawing on recent developments in the aggregate analysis of large radiocarbon databases, here we present and examine different proxies for relative population change between 1050 BC and AD 1500 within this broad region. By using a robust model-testing approach, our analyses document that the growth of pre-Columbian human population over the 1,700 years prior to European colonisation adheres to a logistic model of demographic growth. This suggests that, at an aggregate level, these pre-Columbian populations had likely reached carrying capacity (however high) before the onset of European colonisation. Our analyses also demonstrate that this aggregate scenario shows considerable variability when projected geographically, which bears on our overall understanding of the resilience of past human food procurement strategies. Lastly, our results provide important insights into pre-Columbian demographic trends and offer novel perspectives on demic expansions, language diversification, and subsistence intensification in the Amazonian biome during the late Holocene.