Consciously or unconsciously, most people have explained them only on the basis that different races have different IQs, despite the absence of any evidence for the existence of such differences. My own long experience with technologically "primitive" New Guineans, who were still dependent on stone tools until modern times, suggests that their average intelligence is greater rather than less than that of Europeans.
But if that is so, why did they never develop metal tools or writing? Nowadays we are taught that racist explanations are incorrect or impolite, but we are not told what the correct explanation is. Until we have a correct explanation, we shall gravitate to racist theories by default.
While devoting years to answering these questions, I have often encountered an occupational hazard of authorship; that of being asked by busy journalists to summarise my conclusions in one sentence for busy readers. I do have such a sentence, and here it is: History unfolded differently on different continents because of differences among continental environments, not because of biological differences among peoples.
This conclusion emerges from discoveries in fields that seem remote from human history, such as linguistics, archaeology, molecular biology of disease-causing microbes, crop genetics, animal behaviour, and bio- geography. A convenient starting point is to recognise that, until 13,000 years ago, all humans on all continents were pre-literate, stone-tool- using hunter-gatherers. Changes in that condition depended on ability to domesticate the wild plants and animals that were available locally to yield crops and to form herds of livestock.
But the vast majority of wild plant and animal species do not lend themselves to domestication. For instance, in the case of wild animals the vital prerequisites include a tractable disposition, a willingness to breed in captivity, and acceptance of dominance hierarchies. None of these traits is to be found among gorillas, rhinoceroses, cheetahs and bighorn sheep, and the consequence is that none of them was domesticated.
Only in a few regions of the world - certainly not more than nine, possibly as few as five - was there a sufficient concentration of wild plant and animal species capable of being domesticated and to produce food quickly enough to establish a competitive life-style. The earliest examples of food production of this kind were in two regions of Eurasia, the Fertile Crescent in the Middle East - stretching from Turkey to Iraq - and China.
Several regions of the Americas, sub-Saharan Africa and New Guinea developed food production only later, and in Native Australia it never developed at all. (Who ever heard of a domesticated kangaroo?) From those few areas of domesticated food production and animal husbandry, the art spread to other areas, giving them a head start - and some of them enjoyed a longer head start than others.
For better or worse, the manufacture of tools of conquest and of "civilisation" depended on the growth of food production. No hunter-gatherers have ever developed indigenous writing, or cities or metal tools. The underlying reasons why their successors did so include the storage of food, sedentary living and sharp increases in human population densities. These were made possible by food production, because this enabled some individuals to live off the food grown by others. These professional parasites, who could not have existed anywhere on earth before the rise of food production, included kings and their bureaucrats, standing armies, city-dwellers, scribes, metal-workers, weapon-makers and technological specialists of all types. It is obvious why armies of professional soldiers, equipped with guns or steel swords and backed by the resources of a centralised and literate state, were able to conquer or exterminate stone-tool-using tribes of pre-literate hunter-gatherers. And the reason armies such as these are to be found earliest in Eurasia is because that was where food production happened first.
Most Native Americans and Australians never reached the battlefield to be felled by Eurasian guns and steel. Instead, they died at home of Eurasian germs, to which Eurasians had already developed considerable immune and genetic resistance while Native Americans had none. It is striking that so many epidemic diseases - smallpox, measles, tuberculosis, influenza and others - were introduced by Eurasians to the New World, in return for which Native Americans had no epidemic disease with which to infect invading Europeans (except syphilis - and that is questionable). Those Eurasian germs were the main factor in reducing the native population of the Americas by about 95 per cent within a few centuries of the arrival of the Europeans. The reason for that one-sided transatlantic exchange of germs has emerged from recent molecular biological studies. It transpires that smallpox and other germs that are a human speciality evolved in the past 10,000 years from diseases particular to the animals that humans had domesticated and with whom they had established very close contact. Eurasians had many large domestic animals from which they could get germs. Native Americans had only one, and that was the llama.
Obviously, this brief sketch cannot hope to explain fully the reasons behind the broadest patterns of history. The differing size, degree of isolation and the orientation of the continents are still more factors. But the one-sentence, take-away message remains the same. Europeans were accidental conquerors. Not until the spread of waterwheel technology in Europe after AD800 was northern and western Europe anything more than a backwater that had contributed nothing of fundamental significance to world civilisation. European crops and livestock, alphabets, metal-working techniques and germs were all imported from the societies that flourished in the Fertile Crescent and other parts of Eurasia. Europeans merely had the good fortune to be living on the world's largest, most centrally located continent, which also contained the richest biological resources.
History was forged by differences in geography, not by differences in genes.
Jared Diamond is a professor of physiology at the University of California Medical School, Los Angeles. His book "Guns, Germs and Steel: A Short History of Everybody for the Last 13,000 Years" (Jonathan Cape, pounds 18.99) was last week awarded the prestigious Rhone Poulenc Science Book Prize for 1998.