Modern genetics has now shown that the "out of Africa" theory is correct.by Stephen Oppenheimer / October 20, 2003 / Leave a comment
Published in October 2003 issue of Prospect Magazine
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Humans first emerged in Africa around 2.5m years ago. Over 160,000 years ago a new group-the first “anatomically modern” humans-arose in the lands of east Africa. Every human on earth today is descended from that group. Then, around 80,000 years ago, a splinter group of these new Africans journeyed out of Africa and their descendants spread out to the far reaches of the continents. This incredible journey across land, river and ocean can now be mapped and plotted in time, through a combination of archaeology, climate study and, most recently, the study of genes.
The earliest humans
Our human story really begins 7m years ago, when cool, dry weather devastated the habitat of numerous forest-dwelling African ape species and opened new pastures for those apes that could survive on the savannah. At some point soon afterwards, the first evolutionary steps were taken towards the two-legged, large-brained creature we now call Homo sapiens. The earliest known walking ape, which evolved on the savannah 4.5m years ago, had the same moderately large brain as chimps. But following an intensification of the dry cool phase the first humans-Homo rudolfensis and Homo habilis-appeared about 2.5m years ago. Diminutive, with brains initially not much larger than chimps, they none the less made stone tools and were joined rapidly by Homo ergaster, and then Homo erectus, also both toolmakers. The latter was the Model T for humans, lasting well over 1m years and spreading throughout Africa, Asia and Europe. These early human species and members of their vegetarian sister group Paranthropus (now extinct) were all characterised by a dramatic growth in brain size. The rapidity of that initial brain growth was never to be repeated.
Some new behaviour shared by all these new species must have been behind the selective pressure that began to favour individuals with larger brains. Whatever new behaviour, unique to these two groups of hominids, drove the growth of their brains, it arose long before evidence for complex culture. It seems to have given them a special advantage in this period of drought, since they replaced-in some cases violently-all other hominids apart from forest-dwelling great apes. The most obvious skill which would benefit from a large brain is the one which still clearly separates today’s humans from all other living species: speech. Speech does not depend on diet or toolmaking, which explains how such rapid brain growth could have occurred in vegetarians and omnivores alike while, over the same period, technology apparently languished in both.