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The rise and fall of the third chimpanzee

Plants and animals spread quickly and easily within a climate zone to which they are already adapted. To spread out of this zone, they have to develop new varieties with different climate tolerances. A glance at the map of the Old World on this page shows how species could shift long distances without encountering a change of climate. Many of these shifts proved enormously important in launching farming or herding in new areas, or enriching it in old areas. Species moved between China, India, the Near East, and Europe without ever leaving temperate latitudes of the northern hemisphere. Ironically, the US patriotic song 'America the Beautiful' invokes America's own spacious skies, its amber waves of grain. In reality, the most spacious skies of the northern hemisphere were in the Old World, where amber waves of related grains came to stretch for 7,000 miles from the English Channel to the China Sea.

The Romans were already growing wheat and barley from the Near East, peaches and citrus fruits from China, cucumbers and sesame from India, and hemp and onions from central Asia, along with oats and poppies originating locally in Europe. Horses that spread from the Near East to West Africa revolutionized military tactics there, while sheep and cattle spread down the highlands of East Africa to launch herding in southern Africa among the Hottentots, who lacked locally domesticated animals of their own. African sorghum and cotton reached India by around 2000 BC, while bananas and yams from tropical Southeast Asia crossed the Indian Ocean to enrich agriculture in tropical Africa.

In the New World, however, the temperate zone of North America is isolated from the temperate zone of the Andes and southern South America by thousands of miles of tropics, in which temperate-zone species cannot survive. As a result, the llama, alpaca, and guinea-pig of the Andes never spread in prehistoric times to North America or even to Mexico, which consequently remained without any domestic mammals to carry packs or to produce wool or meat (except for corn-fed edible dogs). Potatoes also failed to spread from the Andes to Mexico or North America, while sunflowers never spread from North America to the Andes. Many crops that were apparently shared prehistorically between North and South America actually occurred as different varieties or even species in the two continents, suggesting that they were domesticated independently in both areas. This seems true, for instance, of cotton, beans, lima beans, chili peppers, and tobacco. Corn did spread from Mexico to both North and South America, but it evidently was not easy, perhaps because of the time it took to develop varieties suited to other latitudes. Not until around 900 ADthousands of years after corn had emerged in Mexicodid corn become a staple food in the Mississippi Valley, thereby triggering the belated rise of the mysterious mound-building civilization of the American Midwest.

Thus, if the Old and New Worlds had each been rotated ninety degrees about their axes, the spread of crops and domestic animals would have been slower in the Old World, faster in the New World. The rates of rise of civilization would have been correspondingly different. Who knows whether that difference would have sufficed to let Montezuma or Atahuallpa invade Europe, despite their lack of horses?

I have argued, then, that continental differences in the rates of rise of civilization were not an accident caused by a few individual geniuses. They were not produced by the biological differences determining the outcome of competition among animal populationsfor example, some populations being able to run faster or digest food more efficiently than others. They also were not the result of average differences among whole peoples in inventiveness; there is no evidence for such differences anyway. Instead, they were determined by biogeography's effect on cultural development. If Europe and Australia had exchanged their human populations twelve thousand years ago, it would have been the former native Australians, transplanted to Europe, who eventually mvaded America and Australia from Europe. Geography sets ground rules for the evolution, both biological and cultural, of all species, including our own. Geography's role in determining our modern political history is even more obvious than the role I have discussed in determining the rate at which we domesticate plants and animals. From this perspective, it is almost funny to read that half of all American schoolchildren do not know where Panama is, but not at all funny when politicians display comparable ignorance. Among the many notorious examples of disasters brought on by politicians ignorant of geography, two must suffice: the unnatural boundaries drawn on the map of Africa by nineteenth-century European colonial powers, thereby undermining the stability of some modern African states that inherited those borders; and the borders of Eastern Europe drawn at the Treaty of Versailles in 1919 by politicians who knew little of that region, thereby helping to fuel the Second World War. Geography used to be a required subject in US schools and colleges until a few decades ago, when it began to be dropped from many curricula. The mistaken belief arose then that geography consisted of little more than memorizing the names of capital cities. But twenty weeks of geography in the seventh grade is not enough to teach our future politicians about the effects that maps really have on us. The fax machines and satellite communications that span the globe cannot erase the differences among us bred by differences in location. In the long run, and on a broad scale, where we live has contributed heavily to making us who we are.