Without seafaring skills and sturdy boats, ancient humans had only two options to leave Africa for Eurasia: by crossing the Straits of Bab el Mandab at the southern end of the Red Sea and from the Nile delta to the Levant at its northern end. Both would have been difficult. The first route demanded extremely low sea level drawn down by continental ice accumulation to narrow the sea crossing, the earliest in the last glacial cycle being around 70 ka ago. The northern route, with no sea crossing, was potentially achievable throughout the history of the genus Homo. But that way is beset to the north and east by deserts with large tracts that today lack natural water sources. To leave Africa by that route seems the most obvious, being reached along the well-watered Nile valley or the Red Sea coast with its abundant marine resources. Yet moving eastwards to Arabia and further would have required climatic windows of opportunity to ensure well-watered corridors: it would be impossible today without an infrastructure of wells; and edible resources are extremely sparse. Remains of anatomically modern humans (AMH) as old as 200 ka and others in the period between 130 to 85 ka have been found around the eastern shores of the Mediterranean. Either of the two routes could have led them there during periods of increased humidity, perhaps in a series of migratory pulses. In the case of an exodus across the Straits of Bab el Mandab, people could have moved northwards along the Red Sea coast of modern Yemen and Arabia to the Levant. However, the record is patchy, and there is no direct fossil evidence to suggest they went further, into southern Asia or Europe in these earlier times. Each early venture may also have ended in extinction.  The first presence of AMH in Asia and Europe, seems to have been tens of thousand years later: about 75 ka and 45 ka, respectively, so far as we know.

Research in the Arabian Peninsula has early recorded human presence from discarded stone artefacts at widely scattered sites, as far east as the UAE and Oman, but whether these were carried by AMH or other human groups is uncertain. Yet geological research suggests that even in the presently forbidding Empty Quarter of Saudi Arabia there were from time to time abundant springs, river networks and even lakes: occasionally climate changes made much of Arabia habitable. Researchers from the University of Southampton (UK) and Shantou University (China), together with colleagues in Jordan, Australia and the Czech Republic have documented further evidence for ‘green’ episodes on the Jordan Plateau – part of the currently hyperarid  Arabian interior (Abbas, M. and 10 others 2023. Human dispersals out of Africa via the Levant. Science Advances, v.9, article eadi6838; DOI: 10.1126/sciadv.adi6838).

Three sites in Jordan reveal wetland sediments incised by now dry channels or wadis, one of which yielded stone tools Luminescence dating of wetland sediment grains shows the times when they were last exposed to sunlight: some between 86 to 65 ka, others between 57 to 43 ka. Together with data from the rest of Arabia the sites help roughly to define routes that would have permitted human migration, though not the actual directions that early AMH might have travelled or their destinations – if any. They may just have wandered around surviving on the resources that they found during short periods of amenable local climate, and vegetation much as do desert dwellers today. Actually to exit Arabia to southern Asia would require migration around what is now the Persian Gulf, where relevant data are lacking and likely to remain so while poor security for research prevails. To get to Europe would require a much more intricate journey through large mountainous tracts to reach the shores of the Black Sea.

See also: Early human migrants followed lush corridor-route out of Africa. Science Daily. 4 October 2023