importance were domesticated in the New World: corn, potatoes, tomatoes, and squash, to name just a few. The answer to this puzzle requires closer scrutiny of corn, the New World's most important crop. Corn is a cereal—that is, a grass with edible starchy seeds, like barley kernels or wheat grains. Cereals still provide most of the calories consumed by the human race. While all civilizations have depended on cereals, different native cereals have been domesticated by different civilizations: for instance, wheat, barley, oats, and rye in the Near East and Europe; rice, foxtail millet, and broomcorn millet in China and Southeast Asia; sorghum, pearl millet, and finger millet in sub- Saharan Africa; but only corn in the New World. Soon after Columbus discovered America, corn was brought back to Europe by early explorers and spread around the globe, and it now exceeds all other crops except wheat in world acreage planted. Why, then, did corn not enable American Indian civilizations to develop as fast as the Old World civilizations fed by wheat and other cereals?
It turns out that corn was a much bigger pain in the neck to domesticate and grow, and gave an inferior product. Those will be fighting words to all of you who, like me, love hot, buttered corn-on-the-cob. Throughout my childhood, I looked forward to late summer as the season to stop at roadside stands and pick out the best- looking fresh ears. Corn is the most important crop in the US today, worth twenty-two billion dollars to us and fifty billion dollars to the world. But before you charge me with slander, please hear me out on the differences between corn and other cereals. The Old World had over a dozen wild grasses that were easy to domesticate and grow. Their large seeds, favoured by the Near East's highly seasonal climate, made their value obvious to incipient farmers. They were easy to harvest
The Old World grains were already productive in the wild, and one can still harvest up to 700 pounds of grain per acre from wild wheat growing naturally on hillsides in the Near East. In a few weeks a family could harvest enough to feed itself for a year. Even before wheat and barley were domesticated, there were sedentary villages in Palestine that had already invented sickles, mortars and pestles, and storage pits, and that were supporting themselves on wild grains. Domestication of wheat and barley was not a conscious act. It was not the case that several hunter-gatherers sat down one day, mourned the extinction of big game animals, discussed which particular wheat plants were best, planted the seeds of those plants, and thereby became farmers the next year. Instead, as I mentioned in Chapter Ten, the process we call domestication—the changes in wild plants under cultivation—was an unintended by-product of people preferring some wild plants over others, and hence accidentally spreading seeds of the preferred plants. In the case of wild cereals, people naturally preferred to harvest ones with big seeds, ones whose seeds were easy to remove from the seed-coverings, and ones with firm non-shattering stalks that held all the seeds together. It took only a few mutations, favoured by this unconscious human selection, to produce the large-seeded, non-shattering cereal varieties that we refer to as domesticated rather than wild. By around 8000 BC, wheat and barley remains from archaeological digs at ancient Near Eastern village sites are beginning to show these changes. The development of bread wheats, other domestic varieties, and intentional sowing soon followed. Gradually, fewer remains of wild foods are found at the sites. By 6000 BC, crop cultivation had been integrated with animal herding into a complete food production system in the Near East. For better or worse (in some major respects worse, as I argued in Chapter Ten), people were no longer hunter- gatherers but farmers and herders, en route to being civilized.
Now contrast these relatively straightforward Old World developments with what happened in the New World. The parts of the Americas where farming began lacked the Near East's highly seasonal climate, and so lacked large-seeded grasses that were already productive in the wild. North American and Mexican Indians did start to domesticate three small-seeded wild grasses called maygrass, little barley, and a wild millet, but these were displaced by the arrival of corn and then of European cereals. Instead, the ancestor of corn was a Mexican wild grass that did have the advantage of big seeds but in other respects hardly seemed like a promising food plant: annual teosinte.
Teosinte ears look so different from corn ears that scientists argued about teosinte's precise role in corn's ancestry till recently, and even now some scientists remain unconvinced. No other crop underwent such drastic changes on domestication as did teosinte. It has only six to twelve kernels per ear, and they are inedible, because they are enclosed in stone-hard cases. One can chew teosinte stalks like sugar cane, as Mexican farmers still do. But no one uses its seeds today, and there is no indication that anyone did prehistorically either.
Hugh Iltis identified the key step in teosinte's becoming useful: a permanent sex change! In teosinte the side branches end in a tassel composed of male flowers; in corn they end in a female structure, the ear. Although that sounds like a drastic difference, it is really a simple hormonally-controlled change that could have been started by a fungus, virus, or change in climate. Once some flowers on the tassel had changed sex to female, they would have produced edible naked grains likely to catch the attention of hungry hunter-gatherers. The tassel's central branch would then have been the beginning of a corn cob. Early Mexican archaeological sites have yielded remains of tiny ears, barely an inch-and-a-half long and much like the tiny ears of our 'Tom Thumb' corn variety.
With that abrupt sex change, teosinte (alias corn) was now finally on the road to domestication. However, in contrast to the case with Near Eastern cereals, thousands of years of development still lay ahead before high- yield corns capable of sustaining villages or cities resulted. The final product was still much more difficult for Indian farmers to manage than were the cereals of Old World farmers. Corn ears had to be harvested individually by hand, rather than
In short, characteristics of the New World's staple food crop made its potential value much harder to discern in the wild plant, harder to develop by domestication, and harder to extract even after domestication. Much of the lag between New World and Old World civilization may have been due to those peculiarities of one plant.
So far, I have discussed geography's biogeographic role, in providing the local wild animal and plant species suitable for domestication. But there is another major role of geography that deserves mention. Each civilization has depended not only on its own food plants domesticated locally, but also on other food plants that arrived after having been first domesticated elsewhere. The predominantly north/south axis of the New World made such diffusion of food plants difficult; the predominantly east/west axis of the Old World made it easy (see map overleaf). Today, we take plant diffusion so much for granted that we seldom stop to think where our foods originated. A typical American or European meal might consist of chicken (of Southeast Asian origin) with corn (from Mexico) or potatoes (from the southern Andes), seasoned with pepper (from India), accompanied by a piece of bread (from Near Eastern wheat) and butter (from Near Eastern cattle), and washed down by a cup of coffee (from Ethiopia). But this diffusion of valued plants and animals did not begin just in modern times: it has been happening for thousands of years.
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
