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 usefuclass="underline" 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 en masse with a sickle; the cobs had to be shucked; the kernels did not fall off but had to be scraped or bitten off; and sowing the seeds involved planting them individually, rather than scattering them en masse. The result was still poorer nutritionally than Old World cereals: lower protein content, deficiencies of nutritionally important amino acids, deficiency of the vitamin niacin (tending to cause the disease pellagra), and need for alkali treatment of the grain to partially overcome these deficiencies.
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 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.