Water alone did not sustain early humans in the desert

Abstract Models of early human dispersal rely on climate to predict where populations could settle, with freshwater availability governing the timing and geography, particularly across the Saharo-Arabian arid belt, where humid windows episodically opened corridors into the desert interior. Yet Pleistocene dispersals into 'Green Arabia' were brief and geographically constrained, a pattern not explained by water availability alone. A 1,300 km geoarchaeological survey through Arabia’s Rub' al Khali, the world’s largest sand sea, found no artefacts or knappable raw materials at palaeolake deposits, despite abundant freshwater and contemporary occupation at the desert margins. Here we show that the accessibility of stone for tool manufacture operated as an independent factor on early human settlement. Spatial modelling confirms that settlement tracked the co-occurrence of water and lithic raw materials across the Arabian Peninsula, with convergent patterns from Africa, North America, and Asia. Dispersal models that omit raw material geology may systematically overestimate the habitable range of stone-tool-dependent populations.