Human speciation
I want to discuss why my view of the early migrations of the human species differs from the broad academic consensus.
Firstly, to work out when and how humans came to be distributed through the world, we rely on archaeology and, more recently, genetics. Neither perspective is without its problems.
- Archaeology depends on sites. The discovery of new sites may change the picture. Archaeologists are biased towards a constantly changing picture. Careers are made by saying something new and interesting, not by confirming what has long been common knowledge.
- Genetic dating depends on mutation rates. These are estimated and, since mutations are random and do not occur at fixed intervals, there is an inevitable margin of error. Furthermore, external factors could have an unknown, systematic effect on the mutation rate. If, for instance, the earth's magnetic field weakened, it would allow more cosmic radiation to reach the surface, possibly elevating the mutation rate.
Archaeologists' and geneticists' models of migration history are evidence-based. This sounds good -- surely our models must be based on evidence -- but means they are subject to caprices of evidence discovery, and uncertainties and revisions of evidence interpretation.
My model is theory-based. Rather than considering only direct evidence for the issue in question, it reflects a broader theory of how human societies operate, based on theories and evidence from a wide range of cultures and historical periods. The point is to build a coherent explanation of the whole of history from a few principles. Incompatibility with specific facts or interpretations, which are subject to the vagaries of academic fashion, does not make or break the theory.
This approach is by no means unscientific. The model makes predictions to be tested against reality. It could be wrong. If it continues to disagree with facts that become increasingly well established, it must either change to accommodate the facts or be abandoned altogether.
I say all this because I choose to start my account of history with a big bang -- the sudden appearance of 'true' human beings in Africa 40 kya (kya = 'thousand years ago'), and their near-instantaneous spread to Europe, Asia, Australia and America. I associate this big bang with a newly evolved ability to manipulate symbols, which I believe underlay art, speculative thinking and 'true' language. In the archaeological record, it corresponds to the transition to the Upper Paleolithic, marked by a new sophistication and variety of stone tools.
My view is by no means original -- the association of a biological event, language skills and the beginnings of human ingenuity was the mainstream view until not long ago. However, it disagrees with some major points of the current academic consensus, which are:
- Modern humans appeared in Africa as much as 190 kya. (Nevertheless, it was long believed, and still is in some quarters, that the emergence of the human species was linked to the appearance of the Upper Paleolithic, which is dated to 40 kya)
- Australia was settled 65 kya. (This was believed to be 40 kya until the 1980s.)
- America was settled about 12 kya. (Increasing numbers of archaeologists think this date should be pushed back at least a few thousand years, with some arguing for dates as early as 40 kya.)
The reason I do not like to believe the human species is as old as 190 ky is that it makes the acceleration of recent times look even more extreme. If it took 150 thousand years to make the step to the Upper Paleolithic, but a hundred years to develop electricity, computing and space flight, it seems we really are in the grip of a runaway process and it can be at most a few thousand years before we conquer the entire universe -- something I find hard to accept.
Such an early date for human origins -- and the implied slowness to move outside Africa and colonise the rest of the world -- also makes humans look much less adventurous than I believe we are.
My prejudices therefore lead me to identify human speciation with the beginning of the Upper Paleolithic -- the point from which growth of mastery over this planet seems to have been almost continuous.
This belief in a link between new technology and a new species can nevertheless be very reasonably criticised. Oppenheimer points out that there is a vast technological gulf between industrial societies and, say, the tribal societies of highland New Guinea, yet both are composed of fully modern humans. There is no compelling reason why the technological revolution of the Upper Paleolithic should have been associated with a step forward in biological evolution.
So I cannot really justify my choice of starting point. All I can say is, let us run with it and see where it gets us.
