Estimating crossing success of human agents across sea straits out of Africa in the Late Pleistocene

Abstract

According to the Out-of-Africa theory, humans originated in Africa and from there expanded into Eurasia. Besides entering Eurasia via a terrestrial route, humans may have used sea straits. These routes would have shaped the subsequent expansions in Eurasia. Sea straits, in particular, are an additional option for entering Eurasia. However, the chances of sea crossings into Eurasia have not yet been quantified.

Here, we apply an agent-based model for human water crossing to quantify the crossing success for the Gibraltar Strait, the Sicily Strait, and the Bab-al-Mandab Strait during the Late Pleistocene. The environment of the model consists of geographic explicit reconstructions of the sea straits, including water temperature, current speed and direction, along with terrestrial data of resource distribution and topography. We tested five behavioral scenarios of water movement skills of Late Pleistocene modern humans in a cold phase, represented by the Last Glacial Maximum, and a warm phase, represented by the Last Interglacial.

We quantified the impact of water movement skills and climate on the crossing success by the crossing success rate (CSR). Our results show that Africa could be left via the Bab-al-Mandab Strait without specific rafting technology. At low sea level, even passive drifting was sufficient to cross the strait. In contrast, the Gibraltar- and Sicily Strait were barriers to humans without rafting technology.