The African Exodus

Sixty thousand years ago, somewhere on the African coast of the Red Sea, a tribal band of probably not more than 150 people left Africa and headed east. Following the coasts of Arabia and India, they quickly reached southeast Asia, crossed 60 miles of open sea to Australia without any way of knowing that a hospitable landfall awaited them, and then proceeded to colonise central and east Asia. Considering that Homo sapiens, not long before, had been reduced almost to the point of extinction, it was a remarkable accomplishment to say the least.

What drove them to leave Africa after staying close to home for more than a millennium? We can only speculate. The developments in language and symbolic thought that had marked “the great leap forward” and were accelerating at the time of the African exodus would have contributed to their ability to navigate such a journey – as would their developing skill in producing more refined stone and bone tools. The last Ice Age was also accelerating, driving early humans out of Africa’s drought-stricken interior to the coastal areas where they had learned to gather food from the sea. Tools from this period found at coastal sites indicate that they could migrate over long distances along the coast of eastern Africa. There was no reason why they couldn’t do the same between continents. All they had to do was cross the narrow strait between present-day Djibouti and Yemen and they had relatively easy access to the endless beaches of southeast Asia.

Were they, like early school-age children, prompted by a growing confidence and curiosity to explore the world beyond what had become familiar? Or was the exodus just a gradual and unwitting expansion of range driven by local conditions? Certainly the speed with which they completed their migration to Australia suggests that they were driven by more than a careless meandering.

Human artefacts from the Northern Territory of Australia (where they landed after crossing from New Guinea) as well as at Lake Mungo (1000 kilometres west of Sydney) are clear evidence that humans were there 60,000 years ago. They would have arrived in sufficient numbers to start a breeding population and then found their way 2000 miles inland from Australia’s north coast to a lush oasis known as the Willandra Lakes. These presumably were descendants of the same people who left Africa, on the other side of the planet, at more or less the same time – 60,000 years ago. Whatever their route from Africa, it allowed for very rapid movement. Exactly how they got there, why they came, and what was driving them are questions we may never be able to answer. We do know, however, that Australia had to be colonised from elsewhere. It had been disconnected from the continents of Eurasia, Africa, and the Americas for 100 million years. So it missed out on all the mammalian, primate, and hominid species that evolution had delivered elsewhere – pursuing instead its own path of placental species like kangaroos. And since humans most assuredly did not evolve from kangaroos, they must have come from somewhere beyond Australia.

Then 10,000 years later, according to the genetic and archaeological evidence, a second wave of migrants followed their curiosity and probably herds of grazing antelope out of Africa – this time to the Middle East. We know the Sahara as the largest desert in the world and a distinctly inhospitable place. But during certain periods of early human history it was a relatively moist region that allowed for human habitation. This had been true from 100,000 to 80,000 years ago – and again for a few thousand years some 50,000 years ago. This would have opened a route along the Red Sea, down the Nile to the Mediterranean, and then eastward across the Sinai to the Levant. Or perhaps this second wave of migrants made their exit, as the first wave probably had, across the 20-kilometre-wide strait of Bab al Mandab into southern Arabia.

However they got there, this was the last substantial exchange between Africa and Eurasia for tens of thousands of years. Another period of glaciations, the Wisconsin Ice Epoch, between 40,000 and 15,000 years ago, turned the Sahara into desert again, effectively closing the door between the two continents and dividing the human world into its African and Eurasian constituents.

The path was now open, however, to the rest of the Eurasian continent and beyond. While the first wave of migrants had taken the southern coastal route of Pakistan and India, this second wave could travel a virtual highway of steppe from the Gulf of Aqaba to northern Iran and on into central Asia and Mongolia. So East Asia was settled by modern humans from both the south and north. Those who took the southern coastal route arrived as early as 50,000 years ago, while those who took the northern route probably entered about 15,000 years later from the steppes of southern Siberia.

About the same time that those on the northern route reached East Asia (i.e. 35,000 years ago), another group from that same route took advantage of a climatic window of opportunity to head west from the central Asian steppes into Europe – into the territory that, until then, had been the preserve of the Neanderthals. Just 5000 years later, they had so dominated the region that their Neanderthal cousins were all but extinct. Known as the Cro-Magnon people (named after the cave in southwest France where some of their bones were first unearthed), they mostly inhabited southern Europe and the Balkans during the depths of the Wisconsin Ice Epoch, and expanded northward during the post-glacial period. They were notable for their advanced culture – called the Aurignacian culture – characterised by a new artistic and inventive genius that found expression in skilfully crafted stone and bone tools, antler-tipped spears, bows and arrows, woven clothing, cooking utensils, musical instruments, and above all in spectacular cave paintings and ivory sculptures.

Meanwhile, those who were following the northern steppe highway eastward had already reached southern Siberia by 40,000 years ago. Their journey seems to have stalled there for the next 20,000 years as they adapted to the frighteningly harsh conditions of the Asian Arctic during the Wisconsin glaciation. So the earliest sites in northeast Siberia date from 20,000 years ago. Considering that they had only relatively recently come from their tropical homeland, one can only imagine the hardships they would have endured in this frozen wilderness. Having honed their hunting skills on the central Asian steppes, they survived mainly on large mammals such as musk ox, reindeer, and mammoths, and eventually followed these herds eastward across the land bridge that had been exposed between Siberia and Alaska. Sea levels had dropped so dramatically during the ice age that the Bering Strait had dried up, allowing these northern pioneers to live a dual Asian-American existence.

At first, it would have been impossible for them to expand southward. A continuous sheet of ice covered most of northern Canada and eastern Alaska, keeping them locked in their northern home. Only when the ice began to retreat some 15,000 years ago were they able to enter the North American plains. Initially it may only have been a few dozen, or a few hundred at most, who made the journey into what must have been happy hunting grounds beyond their wildest dreams – a vast grassland teeming with large grazing animals. Almost immediately their population exploded, and within a thousand years they had journeyed all the way to the tip of South America and driven 75% of all the large mammals in the Americas to extinction. So much for any romantic notion that our indigenous forbears were naturally eco-friendly!

The last chapter in our populating this planet was not written until much later – some 4000 years ago. It was then that those who had long since peopled the islands of southeast Asia, and over thousands of years become both agriculturalists and consummate seafarers, pursued their island-hopping curiosity far out into the Pacific into what would become Polynesia. Despite Thor Heyerdahl’s contention that the Polynesians originated in South America, the linguistic evidence seems clear: Hawaii was settled from southeast Asia. But for all that this last chapter was written relatively recently, it is no less heroic than the exploits of those who first undertook this exodus from Africa 60,000 years ago. Even the most direct route to Hawaii by island-hopping would have required at least two enormous sea passages of a few thousand miles – a voyage on which they would have had to take their own crops, confident in their ability to survive wherever they might find land again. What greater testimony could there be to the irrepressible curiosity of this relatively hairless hominid who left his African homeland so long ago!