A vast number of migrations occurred within the course of human prehistory, just as they did in historical times. Some were doubtless very minor in extent and importance, but others were immensely significant in laying down very resistant and lasting foundation layers beneath the worldwide patterning of human variation. Language families, religions, domesticated animals and major food crops all exist where they do, at least in part, because groups of humans migrated with them at some time in the past. Of course, biological features can spread through gene flow, religions can spread through conversion, and domesticated animals can be traded or exchanged, but these processes operating alone are not enough to explain the full story
Although migration has been an eternal factor throughout human prehistory, there are three highly researched phases of migration in overall human evolution that are currently the foci of a great deal of research:
Migrations of extinct members of the genus Homo, such as Homo erectus and later the Neanderthals, after 2.5 million years ago, within and out of Africa and through Eurasia;
Migrations of ancestral modern humans (H. sapiens) through most of the world, including Australia and the Americas, between 120,000 and 10,000 years ago; migrations of farmers, herders, and boat builders in many separate groups, across most oceans and in all continents except Antarctica, during the past 10,000 years.
There is, of course, a fourth historical and far more recent migration phase, that of the rather staggering diaspora of approximately 150 million people in three massive flows peaking between the 1840 s and the 1950s. One went from western Europe to the Americas and Australasia. Another went from India and China to the Indian Ocean rim, Southeast Asia, and the South Pacific. A third migration spread from Russia and China into central and northeastern Asia (McKeown 2004: 156). These three recent streams indicate that, while migration has always been a continuous activity on a small scale, it has also been subject to major pulses separated by periods of relative quiescence. Perhaps I do not need to add that migration, both forced and free, is still a vital element of our modern society. The refugee crisis that currently perplexes the governments of many countries, including Australia, my adopted home country, is continuing evidence of this.
Some prehistoric migrations seem quite extraordinary to us today The human ability to migrate through vast landscapes and waterscapes to reach and settle new territories is one of the most striking aspects of our shared species history. Easter Island (Isla de Pascua, or Rapa Nui) is isolated across 2000 km of open ocean from its nearest inhabited Polynesian neighbors, Pitcairn and Henderson Islands (Figure 8.4). It was reached soon after ad 1000 by its first Polynesian colonists. They sailed there in one or more outrigger or double canoes with plank sides lashed on to dugout keels, crafted using polished stone tools and propelled by paddles and pandanus matting sails. Between 1000 and 800 years ago, Polynesians achieved this crossing, and many more, to equally isolated islands such as New Zealand, the Marquesas Islands, and Hawaii. Those who might see this as something of a record will be surprised to learn that people related to Polynesians probably made an equally astounding crossing about 2500 years earlier (1500 bc), over 2300 km of open sea from the Philippines to the Mariana Islands in western Micronesia.4
Humans, indeed, are the only mammal species to have colonized all regions of the world capable of supporting life through their own energy and culture. Our domestic animals and plants traveled with us, as did our commensals such as rats, weeds, and viruses, but it was the humans who made these diasporas possible.
Was there a likely common driving factor behind all successful prehistoric migrations? Accidents and disasters (e. g., a storm at sea, a volcanic eruption, or tidal wave) can trigger minor situations of unplanned migration, but only on a small scale. The eruption of Vesuvius in ad 79 did not drive all surviving southern Italians to the other side of the Roman Empire, or indeed cause any measurable hiccup in the development of Roman civilization. It is becoming fashionable nowadays to look for the causes of ancient migrations in climate change, particularly with respect to severe rainfall and temperature variations. I do not doubt the importance of such natural causes, especially for people living in fragile 'edge of the range' environments, where unexpected drought or a shrinkage in the average length of the growing season by a few days could have a disastrous impact on food production. But, in my view, the real energy behind the world's major colonizing migrations was human and demographic, in the sense that increasing human populations required new resources, especially territory, and more so if other groups or declining environmental conditions impinged on a long-term basis on the territories they already held. Shrinking populations would never have made successful colonists if they just continued to shrink, unless by migrating to richer habitats they reversed their demographic trajectory
The question for prehistorians to answer, therefore, is why such demographic engines of expansion evolved in the first place, sufficient to drive peoples, languages, and societies across whole continents? Without migration there would be no human species, at least not outside a small region of Africa.
World History
