The Acheulean niche: climate and ecology predict handaxe production in Europe

The Acheulean was the most spatially and temporally vast stone tool industry produced by early humans, persisting for >1.6 million years across three continents. Understanding how behavioral and artifactual variation in these populations relates to climate change and ecology is vital to correctly interpreting the archaeological record, especially given the major climatic and cultural fluctuations during the Pleistocene. Bifacially flaked core tools - which technologically define the tradition - are sometimes regionally and periodically absent within the Acheulean's boundaries. Biface presence is broadly associated with, but rarely formally tested against, environmental conditions. Here, we investigate biface presence/absence and climate/ecological variation at a continental scale between 726 and 130ka. Using a comprehensive sample of European sites matched to paleoenvironmental reconstructions, we demonstrate clear associations between Acheulean presence and specific environments. Acheulean habitat suitability was most strongly associated with mean winter temperatures above -5/-10 degrees C, and precipitation of the driest month above 15 mm. Two major habitats, warm forest/woodland and shrubland, comprised the European Acheulean niche. Acheulean spatial presence was reconstructed through time: during interglacial and glacial periods it covered most of southwestern Europe, but extended along northern coastal routes during interglacials. Central and Eastern Europe always remained unsuitable. The Acheulean was excluded from areas experiencing both low winter temperatures and low summer precipitation, but reached areas including only one of those two climatic extremes, suggesting seasonal migrations to avoid the harshest seasons. These analyses explain current Acheulean site distributions in Europe and suggest strong links between handaxes, specific ecological conditions, and prehistoric demographic patterns.