Last Interglacial summer heat restricted human migration

Abstract Homo sapiens dispersed in two major waves from Africa. The early dispersal wave had limited success beyond the Arabian Peninsula, although the beginning of this wave coincided with the Last Interglacial period (LIG, 117~127 thousand years ago) when well-watered/vegetated environments formed suitable habitats. The factors hindering this dispersal remain unclear. Here, we estimate the habitability in LIG environments based on a human physiological model and climate patterns that a single human would have encountered during its lifetime. Our climate reconstructions, using an Omani fossil coral and climate modelling, reveal hotter and longer summers in the Arabian Peninsula during the LIG than today due to a weak monsoon and strong insolation. This summer heat exceeded the limit to engaging in hunting-gathering activities and survivability, even in well-watered/vegetated environments. We conclude that extreme summer heat during the LIG could have been the primary barrier hindering the early dispersal beyond/crossing the Arabian Peninsula.