Part three discussed some of our cultural hallmarks and their animal precedents or precursors. Several of those hallmarks are ones that we are proud of, though one (agriculture) has proved to be a mixed blessing and another (chemical abuse) an unmitigated evil. Those cultural hallmarks—especially language, agriculture, and advanced technology—have been the causes of our rise. They are what permitted us to expand over the globe and become world conquerors. That expansion, though, consisted of more than our conquering areas previously unoccupied by the human species. It also involved the expansion of particular human populations that conquered, expelled, or killed other populations. We became conquerors of each other, as well as of the world. Thus, our expansion has been marked by yet another human hallmark that has animal precursors and that we have taken far beyond its animal limits—namely, our propensity to kill other members of our species en masse. Along with our environmental destructiveness, it now poses one of the two potential causes for our fall.
To appreciate our rise to the status of world conquerors, recall that most animal species are distributed over only a small part of the Earth's surface. For example, Hamilton's frog is confined to one forest patch of thirty-seven acres plus one rock-pile covering 720 square yards in New Zealand. The most widespread wild land mammal other than humans used to be the lion, which as of 10,000 years ago occupied most of Africa, much of Eurasia, North America and northern South America. Even at the time of its greatest extent, though, the lion did not reach Southeast Asia, Australia, southern South America, the polar regions, or islands. There are even more widespread bird species that occur on all continents except Antarctica, such as the barn owl or peregrine falcon, but they too are absent from many islands, high elevations, cold climates, and all the oceans.
Humans used to have a typically mammalian restricted distribution, in warm, non-forested areas of Africa. As recently as 50,000 years ago, we were still confined to tropical and mild-temperature areas of Africa and Eurasia. Then we expanded in turn to Australia and New Guinea (around 50,000 years ago), cold parts of Europe (by 30,000 years ago), Siberia (by 20,000 years ago), North and South America (around 11,000 years ago), and Polynesia (between 3,600 and 1,000 years ago). One dramatic stage in this expansion of ours into a large realm formerly without people—the New World—will be the subject of a later chapter, Chapter Eighteen. Today we occupy or at least visit not only all lands but also the surface of all the oceans, and we are starting to probe into space and the oceans' abysses.
In the process of this world conquest, our species underwent a basic change in the relations between its populations. Most animal species with sufficiently wide geographic ranges fall into populations that have contact with neighbouring populations but have little or no contact with distant ones. In this respect, too, humans used to bejust another species of big mammal. Until relatively recently, most people spent their entire lives within a few dozen miles of their birthplace, and had no way of learning even of the existence of people living at much greater distances. Relations between neighbouring tribes were marked by an uneasy shifting balance between trade and xenophobic hostility.
This fragmentation promoted, and was reinforced by, the tendency for each human population to develop its own language and culture. Initially, the massive expansion of our species' geographic range involved a massive increase in our linguistic and cultural diversity. Among the 'new' parts of our range occupied only within the last 50,000 years, New Guinea and North and South America alone came to account for about half of the modern world's languages. Much of that long heritage of cultural diversity has been erased in the last 5,000 years by the expansion of centralized political states. Freedom of travel—a modern invention—is now accelerating that homogenization of our language and culture. However, in a few areas of the world, notably New Guinea, stone-age technology and our traditional xenophobic outlook persisted into the Twentieth Century, giving us a last glimpse of what the rest of the world used to be like. Chapter Thirteen will try to convey some feeling for our pre-homogenized condition, and for what we have lost as well as gained through our new-found mobility.
The outcome of conflicts between expanding human groups has been heavily influenced by group differences in our cultural hallmarks. Especially decisive have been differences in military and maritime technology, in political organization, and in agriculture. Groups with more advanced agriculture thereby acquired the military advantage of larger population numbers, ability to support a permanent military caste, and resistance to infectious diseases against which sparser populations had evolved no defence.
All those cultural differences used to be ascribed to genetic superiority of conquering 'advanced' peoples over conquered 'primitive' ones.
However, no evidence of such genetic superiority has been forthcoming. The likelihood of genetics playing such a role is refuted by the ease with which the most dissimilar human groups have mastered each other's cultural techniques, given adequate learning opportunities. New Guineans born of stone-age parents now pilot aeroplanes, while Amundsen and his Norwegian crew mastered Eskimo dog-sledding methods to reach the South Pole. Instead, one has to ask why some people acquired the cultural advantages that let them conquer other people, despite lack of any evident genetic advantages. For example, was it purely by chance that Bantu peoples originating from equatorial Africa displaced Khoisan people over most of southern Africa, rather than vice versa? While we cannot expect to identify ultimate environmental factors behind small-scale conquests, chance should play less of a role and ultimate factors should be more compelling if we focus on large-scale population shifts over long times. Hence Chapters Fourteen and Fifteen will examine two of the largest-scale shifts in recent history: the modern expansion of Europeans over the New World and Australia; and the perennial puzzle of how Indo-European languages managed earlier to overrun so much of Eurasia from an initially restricted homeland. We shall see clearly in the former case, and more speculatively in the latter, how each human society's culture and competitive position have been shaped by its biological and geographical heritage, especially by the plant and animal species available to it for domestication.
Competition among members of the same species is not unique to humans. Among all animal species as well, the closest competitors are inevitably members of the same species, because they share the closest ecological similarity. What varies greatly among species is the form that competitive strife takes. In the most inconspicuous form, rival animals compete merely by consuming food potentially available to each other and exhibit no overt aggression. Mild escalation involves ritualized displays, or chasing. As a last resort, now documented in many species, rival animals kill each other.
The competing units also vary greatly among animal species. In most songbirds, such as American or European robins, individual males or else male/female pairs face off. Among lions and common chimpanzees, small groups of males who may be brothers fight, sometimes to the death. Packs of wolves or hyenas do battle, while ant colonies engage in large-scale wars with other colonies. Although for some species these contests may end in deaths, there is no animal species whose survival as a species is even remotely threatened by such deaths. Humans compete with each other for territory as do members of most animal species. Because we live in groups, much of our competition has taken the form of wars between adjacent groups, on the model of the wars between ant colonies rather than the small-scale contests between robins. As with adjacent groups of wolves and common chimps, relations of adjacent human tribes were traditionally marked by xenophobic hostility, intermittently relaxed to permit exchanges of mates (and, in our species, of goods as well). Xenophobia comes especially naturally to our species, because so much of our behaviour is culturally rather than genetically specified, and because cultural differences among human populations are so marked. Those features make it easy for us, unlike wolves and chimps, to recognize members of other groups at a glance by their clothes or hair style. What makes human xenophobia much more lethal than chimp xenophobia is of course our recent development of weapons for mass killing at a distance. While Jane Goodall described males of one group of common chimps gradually killing off individuals of the neighbouring group and usurping their territory, those chimps had no means to kill chimps of a more remote group, nor to exterminate all chimps (including themselves). Thus, xenophobic murder has innumerable animal precursors, but only we have developed it to the point of threatening to bring about our fall as a species. Threatening our own existence has now joined art and language as a human hallmark. Hence Chapter Sixteen will survey the history of human genocide, to make clear the ugly tradition from which Dachau's ovens and modern nuclear warfare spring.