Climatic and adaptive constraints for the first humans in western Eurasia.

The study of the environmental context in which the earliest human settlements developed is essential to understand the factors that shaped the dispersal and occupation of territories. To achieve this, the integration of comparable, quantitative palaeoecological proxy data across broad spatial and temporal scales is fundamental. The main objective of this study is to provide a palaeoecological reconstruction of Early Pleistocene sites with and without evidence of human presence, in order to assess ecological differences and evaluate the influence of environmental factors on early human occupation. Several climatic and ecological variables were reconstructed, including temperature, precipitation, seasonality, Net Primary Productivity (NPP), and Total Herbivore Biomass (THB), across sites from Europe, the Caucasus, and the Near East, ranging in age from 2.0 to 0.8 Ma, with Dmanisi (Georgia) representing the oldest and level TD6 of Gran Dolina (Sierra de Atapuerca, Burgos) the most recent. Climatic variables were obtained using the open-access R package pastclim, while NPP values were estimated using the NCEAS model based on mean annual temperature and annual precipitation; THB was subsequently derived from NPP values as an ecological proxy. The PCA results indicated that human presence was associated with ecosystems characterized by intermediate to low ranges of precipitation and productivity, including the lowest values observed, and with comparatively warmer conditions. On the other hand, humans were absent from ecosystems with the highest precipitation and productivity values. The reconstructions presented here constitute a first step toward characterizing the environmental conditions associated with early human settlements and will serve as a foundation for future studies focusing on herbivore mammal communities and the ecological settings of these archaic human groups.