On the map of the world, compare the shapes and orientations of the continents. You'll immediately be struck by an obvious difference. The Americas span a much greater distance north to south (9,000 miles) than east to west (only 3,000 miles at the widest, narrowing to a mere 40 miles at the Isthmus of Panama). That is, the major axis of the Americas is north-south. That's also true, although to a lesser degree, for Africa. In contrast, the major axis of Eurasia is east- west. What effect, if any, did those different orientations of the continents' axes have on human history?
Merely posing this question may raise some people's hackles. It seems to invite the label "environmental determinism" a concept that is sometimes lampooned as implying that human creativity counts for nothing, and that climate irresistibly programs us like computers. Naturally, geographic interpretations can be wrong or carried to an extreme. But denying that geography influences the broad course of history is equally extreme.
Human societies have evolved at different average rates on different continents for at least the past ten thousand years. Specifically, developments such as agriculture, metallurgy, writing, and empires arose earliest in parts of Eurasia, arose later in the Americas and sub-Saharan Africa, and did not arise indigenously in Australia. Such persistent patterns can hardly be dismissed as accidents reflecting where a few geniuses happened to be born. Bigots prefer to invoke supposed differences in I.Q. among populations, but have conspicuously failed to demonstrate such differences. Instead, these broadest patterns of history seem likely to have arisen from influences of differing geographic factors. I believe that the enormous, sometimes tragic, consequences of those differences in the continents' axes contributed greatly to the very different treatment that history has meted out to Native Americans, Africans, and Eurasians in the last 500 years.
My interest in this question has been restimulated by a recently published, revised edition of a wonderful book, Domestication of Plants in the Old World, by Israeli geneticist Daniel Zohary and German botanist Maria Hopf. The book concerns the early importance of that part of Southwest Asia variously known as the Fertile Crescent, or the Near East. This area was the earliest site for a whole stung of developments, including towns, writing, empires, and what we term (for better or worse) civilization. All those developments sprang, in turn, from the advent of dense human populations and the rise of food productionin the form of agriculture and animal husbandrythat made it possible to store food surpluses and feed nonfarming specialists.
Since food production was the first of the major innovations that arose in the Fertile Crescent, anyone attempting to understand the broad pattern of human history must begin by trying to understand why domestication started so early there. Why, too, did it spread from there so fast and so far? Zohary and Hopf are illuminating on both points.
THE FERTILE CRESCENT
The early start in the Fertile Crescent, according to Zohary and Hopf, was due to a combination of geographic, climatic, and biotic factors. Western Eurasia (Europe plus Southwest Asia) includes the world's largest zone of so called Mediterranean climate, characterized by mild, wet winters and hot, dry summers. The world's other Mediterranean zones are the Cape of South Africa, the central coast of Chile, parts of southern Australia, and my homeland of coastal California. Among those Mediterranean zones, western Eurasia's is not only the largest but may also experience the greatest climatic variation between seasons and years. That climate favored the evolution of annual plants that survived the long, dry summer by putting much of their energy into big, edible seeds, while leaving the inedible remainder of the plant to die back and regrow each year. Because of the Fertile Crescent's extreme Mediterranean climate, its plants provided hungry humans with an exceptionally high percentage of annuals.
The region also has a high percentage of hermaphroditic, predominantly selfpollinating annuals that is, ones that usually pollinate themselves but are occasionally cross- pollinated. As Zohary and Hopf explain, that feature was also good for the first farmers. Occasional cross-pollination generated several strains to choose from, while the predominant self-pollination insured that varieties selected as superior usually perpetuated themselves unchanged and were not immediately lost by hybridization with less desirable strains.
Some of those big-seeded, self-pollinating annuals, such as the wild ancestors of barley and wheats, were so abundant as wild stands in the Fertile Crescent that they were already being collected by hunter-gatherers before the emergence of farming. Eventually, people began to increase their yields of those wild plants by tilling soil, intentionally sowing seeds, harvesting, and threshing. That new system unintentionally transformed the wild plants into cultivated varieties because people naturally preferred to sow, grow, eat, and resow seeds of those particular plant varieties with desirable features. Depending on the plant species, those features might include larger seeds, a less bitter taste, more uniform germination, and seeds that remain on the parent plant.
The Fertile Crescent also offered other advantages to incipient farmers. Its range of elevations, from the lowest spot on earth (the Dead Sea) to mountains nearly 17,000 feet high, meant that within a short distance there was a corresponding range of environments, hence a great diversity of wild plants available for potential domestication. These varied environments also harbored many species of large wild mammals, some of which were the ancestors of our most important domesticated mammals today. Southwest Asia's few large rivers and short coastline provided scant aquatic resources to make the hunter-gatherer life style competitive with incipient farming. Climatic changes about ten thousand years ago at the end of the Pleistocenechanges that exterminated some large mammal species and expanded habitats rich in annual plants ancestral to cropsquickly tipped the balance from hunting and gathering to domestication.
By about 8000 B.C., the peoples of the Fertile Crescent were domesticating numerous valuable plants. Most of the calories consumed by those first farmers came from high-carbohydrate cereals such as wheat and barley, the most useful of the dozens of wild cereal species in the area by virtue of their large seeds, abundance, and annual growth. Unlike protein-poor corn and rice, which became the leading cereals of the Americas and eastern Asia respectively, the wheels of the Fertile Crescent had a substantial protein content of 8 to 14 percent.
During or soon after the onset of farming in Mesopotamia, these starchy cereals were complemented by two types of food with an even higher protein content: legumes, especially peas and lentils, which have 20 to 25 percent protein, and domestic animals (sheep, goats, came, and pigs) The animals yielded wool and leather as well. One other crop, flax, not only filled out the dietary trinity of carbohydrate, protein, and fat with its very oily seeds but also provided the oldest cultivated source of plant fiber for making clothes. Linen from flax reigned supreme as Europe's preferred plant textile material until it was finally replaced by cotton and synthetics during and after the Industrial Revolution. Thus, the Fertile Crescent's first farmers assembled a balanced package for intensive food production, based on eight main crops and four animals that filled humanity's basic economic needs: carbohydrate, protein, fat, clothing, and, eventually, milk products and animal transport.
RATIONAL OUTWARD
Soon after food production arose in the Fertile Crescent, it radiated into other parts of western Eurasia and North Africa, spreading progressively farther west and east. In a striking map, Zohary and Hopf illustrate how agriculture reached Greece and Cyprus by 7000 B.C., Egypt and India soon after 6000 B.C., central Europe by 5400 B.C., and Britain about 4000 B.C. (These are so-called calibrated radiocarbon datesdates based on the regular decay of the radioactive isotope carbon- 14 and corrected for slight fluctuations in atmospheric isotope with time.) Food production in the new areas was launched by the crucial package of the same domesticated plant and animal species that launched it in the Fertile Crescent.
Of course, not all pieces of the package spread to all those outlying areas: for example, Egypt was too warm for einkorn wheat lo become established. Some inhabitants of outlying areas went on to domesticate a few local crops of their own, such as poppies in western Europe. But most food production in these regions depended at first on the same group of Fertile Crescent domesticates. Their spread was soon followed by the spread of other innovations originating in or near Mesopotamia, including the wheel, writing, metalworking techniques, milking, fruit trees, and beer and wine production.
Why did the same plant package launch food production throughout western Eurasia ? Was the same set of wild plants found useful in many areas and independently domesticated? No, that's not the case. Many of the Fertile Crescent's "founder crops" (to use Zohary's and Hopf's term) don't even occur in the wild outside Southwest Asia. In Egypt, for instance, of the eight main founder crops, only barley grows wild. Egypt's Nile Valley provides an environment similar to that of the Tigris and Euphrates Valley, so the package that worked well in Mesopotamia also worked well enough in the Nile Valley to trigger the spectacular rise of indigenous Egyptian civilization. The Sphinx and the pyramids, then, were built by people fed on crops originating in the Fertile Crescent, not in Egypt.
Wild ancestors of crops that were first domesticated in Southwest Asia also existed in Europe, Asia, and India. but we can be confident that the crops first produced there were mostly obtained from Southwest Asia and were not local domesticates . All modern cultivated varieties of most of the Fertile Crescent's founding crops either share only one arrangement of chromosomes out of multiple arrangements found in the wild ancestor, or else they share only a single mutation (out of many possible mutations) by which the cultivated varieties differ from the wild ancestor in characteristics desirable to humans. For instance, all cultivated peas share the same recessive gene that prevents ripe pods from spontaneously popping open and spilling their peas, as wild pea pods do. Evidently, most of the Fertile Crescent's founder crops were never domesticated again elsewhere after their initial domestication. Had they been repeatedly domesticated independently, they would exhibit legacies of those multiple origins in the form of varied chromosomal arrangements or varied mutations.
The ancestors of most of the founder crops have multiple wild relatives, in the Fertile Crescent and elsewhere, that would also have been suitable for domestication. For example, peas belong to the genus Pisum, which consists of two wild species: f:! sativum, the one that became domesticated to yield our garden peas, and the common and widespread P. fulvum, which was never domesticated. Yet the taller taste good, either fresh or dried. Similarly, domesticated wheat, barley, lentils, chickpeas, beans, and flax all have numerous wild relatives. Some of those related beans and barleys were indeed domesticated independently in the Americas or China. but in the Near East only one of several potentially useful wild species of a given plant was domesticatedprobably because it spread so quickly that people soon stopped gathering the other wild relatives and ate only the crop. A Zohary and Hopf emphasize, the crop 's rapid spread preempted any possible further attempts to domesticate its relatives or to redomesticate its ancestor.
Why was the spread of crops from the Fertile Crescent so rapid? The answer has to do with that east-west axis of Eurasia. Localities east and west of one another at the same latitude share exactly the same seasonal variations in day length. To a lesser extent, they also tend to share similar diseases, temperature, and rainfall. For example, southern Italy, northern Iran. and Japan, all located at about the same latitude but lying thousands of miles apart, are more similar to one another in climate than each is lo a location lying a mere 1,0()0 miles due south. And the germination, growth, and disease resistance of plants there are adapted to precisely those features of climate. As a consequence, most of the Fertile Crescent crops grow well in southern Europe and Japan, but grow poorly at the equator.
In other words, Fertile Crescent domesticates spread west and east so rapidly because they were already well adapted to the climates of the regions to which they were spreading. Once farming crossed from the plains of Hungary into central Europe about 5400 B.C., it spread so quickly that the sites of the first farmers in the vast areas from Poland west to Holland (marked by their characteristic pottery with linear decorations) were nearly contemporary. By the time of Christ, cereals of Fertile Crescent origin were growing over the 1 0,000-mile expanse from the Atlantic coast of Ireland to the Pacific coast of Japan. That west-east expanse of Eurasia is the largest land distance on earth.
Thus, Eurasia's west-east axis allowed Fertile Crescent agriculture to spread over the band of temperate latitudes from Ireland to the Indus Valley and to enrich the agriculture that arose independently in eastern Asia Conversely Eurasian crops that were first domesticated far from the Fertile Crescent but at the same latitudes were able to spread back to the Near East. Today, when seeds are transported over the whole globe by ship and plane, we take for granted that our meals are a geographic mishmash. A typical American fast-food restaurant meal would include chicken (first domesticated in Southeast Asia) and potatoes (from the Andes) or corn (from Mexico), seasoned with pepper (from India), and washed down with a cup of coffee (of Ethiopian origin). But 2,000 years ago, Romans were already nourishing themselves with a range of foods that Zohary and Hopf show to have mostly originated elsewhere. Of Roman crops, only oats and poppies