Code associated to the paper "Environmental conditions shaped the patterns of initial expansion by anatomically modern humans" by Frédérik Saltré, Joël Chadœuf, Thomas Higham, Monty Ochocki, Sebastián Block, Ellyse Bunney, Bastien Llamas, and Corey J. A. Bradshaw

The ability of our ancestors to switch food sources and to migrate to more favourable environments quickly enabled the rapid global expansion of anatomically modern humans beyond Africa as early as 120,000 years ago1. Whether this versatility was largely the result of environmentally determined processes1-4 or was instead dominated by cultural drivers, social structures, and interactions among different groups5 is unclear6. We developed a new statistical approach that combines both archaeological and genetic data to infer the most-likely initial expansion routes in Eurasia and the Americas. We then quantified the main differences in past environmental conditions between the most-likely routes and other potential (less-likely) routes of expansion. We established that, even though cultural drivers remain plausible at a finer scales, the migration corridors are predominantly constrained by a combination of particular regional environmental conditions, including the presence of a forest-grassland ecotone, changes in temperature and precipitation, and proximity to rivers.

Frederik Saltre, Flinders University, frederik.saltre@flinders.edu.au April 2022