One way in which fully modern humans might have migrated from Africa to colonise the rest of the Old World is by following shorelines. The Kenyan ecologist and anthropologist Jonathan Kingdon coined the term ‘strandloping’ for such a lifestyle. By concentrating on abundant marine life at the waters edge, the strandlopers would be able to bypass the great deserts of North Africa and the Middle East that today bar the way east to anyone foolish enough to walk – water is only available from deep wells, a recent bit of technology. At the time when we know that migration did begin – before the 60 thousand year first occupation of Australasia by modern humans – much drier tropical conditions associated with global cooling would have enlarged these desert barriers enormously.
The problem is that, apart from evidence for coastal life by early humans near to Cape Town in South Africa, it was widely held to be a strategy only adopted at the depth of the last ice age. Most sites would have been drowned by sea-level rise, following ice-sheet melting about 10 thousand years back, to become inaccessible. A multinational team has discovered a rich haul of stone tools and food remains in an uplifted coral reef on the Red Sea shoreline in Eritrea, NE Africa (R.C. Walter and 11 others, 2000. Early human occupation of the Red Sea coast of Eritrea during the last interglacial. Nature, vol 405, pp. 65-68). This turns out to be 125 thousand years old, from the time when climate conditions were similar to those today.
The find shows that modern humans were well adapted to life by the seaside much earlier than previously thought. Since the occupation was at a time of warm, wet climate, strandloping must have been by choice rather than necessity. Quite likely it was adopted by earlier Africans when times were far harder in the previous ice age. When conditions cooled and dried again, well-established strandloping opened the coastal routes to the east, perhaps explaining colonization of New Guinea and Australia 20 to 30 thousand years earlier than much closer Europe. That had to be by boat or raft, for even maximum fall in sea level because of the build up of land ice would not have bared the sea bed between Australasia and modern Indonesia.
How Africans got to Europe is not so easy to explain. Following the Red Sea would have taken them to Suez, a short distance from the Mediterranean but even today one that is inhospitable. But what inducement or pressure would have diverted them from simply continuing around Arabia?