The Great Divide

speculation, albeit informed speculation – that should not deter us. A
     few years ago, it would have been impossible to answer these sorts of question but now,
     thanks to developments in biology (in particular genetics), in geology, in cosmology,
     climatology, linguistics and mythology we understand far more about our deep history
     than ever before. The conclusions we are able to draw, however tentative, are
     worth the effort.
     
    O UT OF A FRICA
    Because of the discovery of DNA , genes, and
     in particular mitochondrial DNA (normally written as mt DNA and inherited only through the mother), and the Y-chromosome
     (which determines male sexuality), and because we know the rate at which DNA mutates, it has become possible – through the
     comparative analysis of the DNA of modern peoples right across
     the globe – to assess who is related to whom, both now and at various times in
     the past. * In effect mt DNA gives us, as one expert put it, ‘a cumulative history of our own
     maternal prehistory’, while the Y-chromosome does the same for our paternal
     history. For our purposes, the main elements in this theoretical picture (much of which
     is still to be confirmed archaeologically) are as follows:
Modern humans evolved in Africa around 150,000 years ago.
Perhaps as early as 125,000 years ago, a group of humans left Africa, most likely
     across the Bab al-Mandab Strait, at the southern end of the Red Sea (when that sea
     was some 230 feet lower than it is now) and travelled across the southern Arabian
     peninsula at a time when the region was much wetter than now, occupied by lakes and
     rivers. No human remains have been found, but primitive stone tools, similar to
     those produced in Africa at much the same time by Homo sapiens , have been
     excavated at Jebel Faya, a rock shelter near the Strait of Hormuz. Genetic evidence,
     of individuals across the world, alive now, shows that all non-African people
     are descended from one small group that must have passed through the Arabian
     peninsula. During very dry periods, the Jebel Faya population may have been isolated
     for hundreds or even thousands of years, before moving on, eastwards, along river
     routes that are now submerged in the Gulf. In this way they would have avoided the
     arid inland deserts of the region, eventually reaching India, by way of the Iranian
     and Pakistan coasts. This ‘beachcombing’ theory about the peopling of
     the world is still only that, a theory, but it is supported by the genetic evidence
     and by the presence of ancient shell middens on many coastal sites. Furthermore, we
     now know that, for much of human existence, before 6,000 years ago, sea levels were
     lower than now and as a consequence there was at that time perhaps as much as 16
     million square kilometres more dry land in the world than there is now, ten per cent
     of the inhabited areas of the globe, a significant and attractive resource. We also
     know that, in general, marine/littoral environments provide a richer nutritional
     environment and support higher population densities and more sedentary settlements
     than do inland sites. Hunter-gatherers in ancient coastal and landbridge areas have
     so far been peripheral to human prehistory but that looks as though it is in the
     process of changing.
This group that left Africa may not have been very large: Y-chromo-some studies
     suggest it perhaps comprised only about 1,000 men of reproductive age and the same
     number of women. Add on children and older people and this represents a population
     of perhaps 5,000. They may not all have gone together, either. Studies of foragers
     show that they like to live in groups of about 150, though when they ceased
     beachcombing, in Australia for example, they formed tribes of between 500 and 1,000
     people (which is what the European colonisers found when they arrived in Australia
     at the end of the eighteenth century).
After 70,000 years ago, humans crossed into Australia.
At 50,000–46,000 years ago, in what is now Iran/Afghanistan, a group left the
     coast and travelled north and west, to populate Europe.
About 40,000 years ago, a second bifurcation took place, this time in Pakistan/north
     India, with another group travelling inland into central Asia.
At about the same time, the ‘beachcombers’ had reached China,
     travelling around the ‘corner’ of South East Asia, and then moving
     inland, back west, along what would become much later the Silk