Jared Diamond asks why Europeans came to dominate and colonise the world and not the peoples of Africa, Australia or America?

Eurasians, especially peoples of Europe and eastern Asia, have spread around the globe. They and their overseas descendants now dominate the modern world in wealth and power. Other peoples, including most Africans, survived and have thrown off European domination but remain far behind in wealth and power. Still others, including the original inhabitants of Australia, the Americas, and southern Africa, are no longer masters of their own lands but have been decimated, subjugated and even exterminated by European colonialists. Why did history turn out that way, instead of the opposite way? Why were American Indians, Africans, and Aboriginal Australians not the ones who conquered or exterminated Europeans and Asians?

To appreciate how non-obvious is the answer to this question, imagine that a historically minded intelligent being from Outer Space had visited the earth 50,000 years ago. If that visitor had been asked to predict which continent's people would develop technology most rapidly and who would conquer whom, what would the extraterrestrial have predicted? The visitor might well have answered "Africa" because human history there had a six million year head start over history on the other continents. The visitor might also have reasonably predicted "Australia," the continent with perhaps the earliest evidence of anatomically and behaviourally fully modern humans, and with by far the earliest evidence for human use of watercraft. The visitor would surely have written off Europe, where anatomically modern Homo sapiens still had not arrived as of 50,000 years ago. To that visitor, the state of the modern world would be unexpected. What are the reasons for the unexpected outcome?

Readers may be beginning to wonder: is this going to be a glorification of so-called progress? Will it be a justification of the status quo, with all its gross injustices? Will it be an apology for racism? I should therefore make two things clear.

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First, I don't hold political and economic development to be an unmitigated good for the human species. It is debatable whether most people alive today are happier or healthier than most hunter/gatherers used to be. We today are certainly at more imminent risk of self-destruction than were our ancestors of 11,000 years ago.

Second, I want to make clear that this is not a piece about differences in IQ, and that it will not assert that Europeans are smarter than other peoples. Many Europeans tacitly assume so, even though they may have learned that it is no longer considered politically correct to say so in public. Technologically primitive peoples are often considered to be biologically primitive.

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Many psychologists, especially in the United States, have tried unsuccessfully to document IQ differences among different peoples. My own anecdotal perception, from my 30 years of work in New Guinea, is that New Guineans appear on the average considerably more intelligent than Europeans. On reflection, that outcome is unsurprising; natural selection related to intelligence operates much more ruthlessly in traditional New Guinea societies than in politically organised Europe, so that New Guineans probably have an average genetic advantage. In addition, most European children today suffer from the crippling developmental disadvantage of spending much of their time being passively entertained by radio, television and movies, while traditional New Guinea children spend all of their waking time talking or otherwise active with other children and adults.

We therefore have to turn the usual racist assumption on its head. Instead of asking how industrial peoples came to be smarter, we must ask: why is it that modern Stone Age peoples, despite probably being genetically smarter and undoubtedly being developmentally advantaged, were nevertheless technologically outstripped and conquered by Eurasians?

I believe the answer to these questions about such broad patterns of history lies in differences among the biological and geographical environments in which different peoples found themselves.

As a continental comparison, let us consider the collision of the Old World and the New World that began with Columbus's voyage in 1492. Most of us are familiar with the stories of how a few hundred Spaniards under Cortes overthrew the Aztec Empire, and how another few hundred under Pizarro overthrew the Inca Empire. The populations of each of those empires numbered millions, possibly tens of millions. At the Inca city of Cajamarca in modern Peru, when Pizarro captured the Inca Emperor Atahualpa in 1532, Pizarro's Spaniards consisted of only 62 soldiers on horseback plus 106 footsoldiers, while Atahualpa was leading an Inca army of about 40,000 soldiers.

Most of us are also familiar with the frequently gruesome details of how other Europeans conquered other parts of the New World. The result is that Europeans came to settle and dominate most of the New World, while the Native American population declined drastically from its level as of 1492. Why did it happen that way? Why did it not instead happen that Montezuma or Atahualpa led the Aztecs or Incas to conquer Europe?

The proximate reasons are obvious. Invading Europeans had steel swords and guns, while Native Americans had only stone and wooden weapons. Just as elsewhere in the world, horses gave the invading Spaniards another big advantage in their conquests of the Incas and Aztecs. From prehistoric times until the First World War, the speed of attack and retreat that a horse permitted, the shock of its charge and the raised fighting platform that it provided left footsoldiers nearly helpless in the open. Steel swords, guns, and horses were the military advantages that repeatedly enabled troops of a few dozen mounted Spaniards to defeat Indian armies numbering in the thousands.

Nevertheless, guns, steel swords and horses were not the sole proximate factors in the European conquest of the New World. The Indians killed in battle by guns and swords were far outnumbered by those killed in bed by infectious diseases such as smallpox and measles. Those diseases were endemic in Europe, and Europeans had had time to develop both genetic and immune resistance to them, but Indians initially had no such resistance. Diseases that were introduced with Europeans killed an estimated 95 per cent of the New World's Indian population.

Finally, there is still another set of proximate factors to be considered. How is it that Pizarro and Cortes reached the New World at all, before Aztec and Inca conquistadores could reach Europe? That depended in the first instance on ships reliably capable of crossing oceans. Europeans had such ships, while the Aztecs and Incas did not. Those ships were backed by the political organization that enabled Spain and other European countries to finance, build, staff and equip the ships. Equally crucial was the role of writing in permitting the quick spread of accurate detailed information, including maps, sailing directions, and accounts by earlier voyagers to motivate later explorers. Writing may also be relevant to what seems to us today the incredible naivety that permitted Atahualpa to walk into Pizarro's trap and permitted Montezuma to mistake Cortes for a returning god. Since the Incas had no writing and the Aztecs had only a short tradition of writing, they did not inherit knowledge of thousands of years of written history. That may have left them less able to anticipate a wide range of human behaviour and dirty tricks, and made Pizarro and Cortes better able to do so.

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I have identified a series of proximate factors behind European colonisation of the New World: ships, political organisation and writing that brought Europeans to the New World; European germs that killed most Indians before they could reach the battlefield; and guns, steel swords and horses that gave Europeans a big advantage on the battlefield. Why did these proximate advantages go to the Old rather than to the New World?

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Theoretically, American Indians might have been the ones to develop steel swords and guns first, to develop ocean-going ships and empires and writing first, to be mounted on domestic animals more terrifying than horses and to bear germs worse than smallpox.

The part of that question that is easiest to answer concerns the reasons why Eurasia evolved the nastiest germs. It is striking that American Indians evolved no devastating epidemic diseases to give to Europeans, in return for the many devastating epidemic diseases that they received from the Old World.

There are two straightforward reasons for this gross imbalance. First, most of our familiar epidemic diseases can sustain themselves only in large dense human populations concentrated in villages and cities, which arose much earlier in the Old than in the New World. Second, most human epidemic diseases evolved from similar epidemic diseases of the domestic animals with which we came into close contact. For example, measles arose from a disease of our dogs, influenza from a disease of pigs, smallpox from a disease of cows, and falciparum malaria from a disease of birds such as chickens. The Americas had very few native domesticated animal species from which humans could acquire diseases: just the llama/alpaca (varieties of the same ancestral species) and guinea pig in the Andes, the Muscovy duck in tropical South America, the turkey in Mexico, and the dog throughout the Americas. In contrast, think of all the domesticated animal species native to Eurasia: the horse, cow, sheep, goat, pig and dog throughout Eurasia; many local domesticates, like water buffalo and reindeer; many domesticated small mammals, such as cats and rabbits; and many domesticated birds, including chickens, geese, and mallard ducks.

So why were there far more species of domesticated animals in Eurasia than in the Americas? Since the Americas harbour over 1,000 native wild mammal species and several thousand wild bird species, you might initially suppose that the Americas offered plenty of starting material for domestication.

In fact, only a tiny fraction of wild mammal and bird species has been successfully domesticated, because domestication requires that a wild animal fulfil many prerequisites: a diet that humans can supply, a sufficiently rapid growth rate, willingness to breed in captivity, tractable disposition, a social structure involving submissive behaviour towards dominant members of the same species (a behaviour transferable to dominant humans), and lack of tendency to panic when fenced. Thousands of years ago, humans domesticated every possible large wild mammal species worth domesticating, with the result that there have been no significant additions in modern times, despite the efforts of modern science.

Eurasia ended up with the most domesticated animal species in part because it is the world's largest land mass and offered the most wild species to begin with. That pre-existing difference was magnified 11,000 years ago at the end of the last Ice Age, when more than 80 per cent of the large mammal species of North and South America became extinct, probably exterminated by the first arriving Indians. Those extinctions included several species that might have furnished useful domesticated animals had they survived, such as North American horses and camels. As a result, American Indians inherited far fewer species of big wild mammals than did Eurasians, leaving them only with the llama/alpaca as a domesticate. Differences between the Old and New Worlds in domesticated plants are qualitatively similar to these differences in domesticated mammals, though the difference is not so extreme.

A further reason for the higher local diversity of domesticated plants and animals in Eurasia than in the Americas is that Eurasia's main axis is east/west, whereas the main axis of the Americas is north/south. Eurasia's east/west axis meant that species domesticated in one part of Eurasia could easily spread thousands of miles at the same latitude, encountering the same day-length and climate to which they were already adapted. As a result, chickens and citrus fruit domesticated in Southeast Asia quickly spread westwards to Europe, horses domesticated in the Ukraine quickly spread eastwards to China, and the sheep, goats, cattle, wheat, and barley of the Mideast quickly spread both west and east. In contrast, the north/south axis of the Americas meant that species domesticated in one area could not spread from Mexico to the Andes; llamas/alpacas never spread from the Andes to Mexico, so that the Indian civilisations of Central and North America remained entirely without pack animals; and it took thousands of years for the corn that evolved in Mexico's climate to become modified into a corn adapted to the shorter growing season and seasonally changing day-length of North America. Similar environmental factors moulded the histories of Africa and Aboriginal Australia as well.

Eurasia's domesticated plants and animals were important for several other reasons besides letting Europeans develop nasty germs. Domesticated plants and animals yield far more calories per acre than do wild habitats, in which most species are inedible to humans. As a result, populations of farmers and herders are typically ten to 100 times greater than those of hunter/gatherers. That fact alone explains why farmers and herders almost everywhere in the world have been able to push hunter/gatherers out of land suitable for farming and herding. Domestic animals revolutionised land transport. They also revolutionised agriculture, by letting one farmer plough and manure much more land than the farmer could till or manure by his/her own efforts. In addition, hunter/gatherer societies tend to be egalitarian and have no political organization beyond the level of the band or tribe, whereas the food surpluses and storage made possible by agriculture permitted the development of political elites. The food surpluses produced by farmers also accelerated the development of technology, by supporting craftspeople who did not raise their own food and could instead devote themselves to developing metallurgy, writing, swords, and guns. Those professional specialists supported by agriculture also included full-time soldiers. That gave a decisive military advantage to many colonising empires. For example, it was the decisive factor in the eventual success of New Zealand's British colonists at defeating New Zealand's indigenous Maori population who were tough and well-armed fighters. While the Maori won some stunning temporary victories, each Maori man could fight for only a short time before having to go home to tend his garden. The Maori were eventually worn down by the full-time soldiers of the British colonists.

As for the meaning of this whirlwind tour of the past, it is that our history has been moulded by our environment. The broadest pattern of human history - namely, the differences between human societies on different continents - seems to me to be attributable to differences in continental environments, not to differences in human biology. In particular, the availability of wild plant and animal species suitable for domestication, and the ease with which those species could spread without encountering unsuitable climates, have contributed decisively to the varying rates of rise of agriculture and herding, which in turn have contributed decisively to human population numbers, population densities, and food surpluses, which in turn contributed decisively to the development of writing, technology and political organisation.

As a biologist also at home in laboratory experimental science, I am aware that these interpretations may be dismissed as unprovable speculation, because they are not founded on replicated laboratory experiments. The same objection can be raised against any of the historical sciences, including astronomy, evolutionary biology, geology and paleontology. It can, of course, be raised against the entire field of history. That is the reason why we are uncomfortable about considering history as a science: it is classified as a social science, which is not considered quite scientific. But remember that the word "science" is not derived from the Latin word for "replicated laboratory experiment", but from the Latin word for "knowledge". In many sciences replicated laboratory experiments would be immoral, illegal or impossible. We cannot manipulate stars while maintaining other stars as controls, nor can we start and stop ice ages, nor can we experiment with evolving dinosaurs. Nevertheless, we can still gain considerable insight into these historical fields by other means. We should surely be able, then, to understand human history, since introspection and preserved writings give us far more insights into the ways of past humans than of dinosaurs.

Jared Diamond is professor of physiology at the University of California, Los Angeles. This is an edited extract from his 1995 Darwin lecture, "Evolution of Guns and Germs".

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