Niche dynamics of Palaeolithic modern humans during the settlement of the Palaearctic

Aim During the Late Pleistocene (c. 126-10 ka), modern humans (Homo sapiens) expanded their geographical range across Eurasia and eventually colonized the Americas. Although the routes by which they migrated have been intensively analysed, the dynamics of their realized climatic niche are still largely unknown. We assess temporal changes in the climatic niche of modern humans, the geographical distribution of their climatic niche and whether niche dynamics correlate with the magnitude of climate change and cultural advances, between 46 and 11 ka. Location Palaearctic. Methods Using the radiocarbon dated archaeological record and spatial palaeoclimatic simulations, we quantify different parameters of the realized climatic niche of modern humans (niche overlap, niche breadth and climatic marginality) between consecutive 1000-2000 year intervals. Moreover, using climate envelope models, we map the potential distributions of modern humans for each time interval and identify the regions that remained more climatically suitable and stable for modern humans through time. Results Between 46 and 22 ka the climatic niche of modern humans expanded, including periods of intense growth in niche breadth at 40 and 30 ka. Changes in seasonal water availability and technological innovations partly correlate with dynamics in niche parameters. We document a persistent climatically suitable mid-latitude belt in south Siberia linking western Europe to the Far East that may have facilitated human migration, and a potential climatic refugium in Beringia. Main conclusions The climatic niche of modern humans changed across the Late Pleistocene, as the result of both climatic and cultural changes. These populations of hunter-gatherers occupied novel climatic conditions but also remained in previously occupied areas under changing climates during the settlement of the Palaearctic. Our approach can provide clues as to where early modern humans may have overlapped in geographical and environmental space with Neanderthals or Denisovans, as evidenced by their contribution to the genetic heritage of some current populations.