The Natural History of the Present, Chapter 8

Chapter 8: What was Wrong with the Edible Landscape? Why Agriculture?

The reasons for the adoption of agriculture are a mystery. A writer has summed up the effects of agriculture on human populations as malnutrition, periodic starvation, epidemic diseases and class division; he might have also included ‘civilization.’ Population pressure is the usual explanation. In most parts of the world horticulture closely followed the extinction of the Pleistocene large mammals. (Some people found other solutions to decreasing supplies of wild foods or expanding human populations. The Hawaiians—also horticulturalists—fattened mullet in tidal pools, while the Aborigines of southeastern Australia built weirs that created vast seasonal swamps for the production of eels. The eels were traded.) Animal herding is supposed to have preceded agriculture, but grains were being grown 12,000 years ago in the Near East, 1500 years before the usual dates given for the domestication of sheep. Signs of domestication are not always easy to read and the herding of semi-domesticated sheep and goats, as the Lapps and the Siberian tribes herd reindeer, may have preceded all this, while the first domesticated plant may have been figs. The large mammal extinctions coincided with rising seas and a warming and drying climate. Rising sea levels flooded continental shelves and ocean banks. Some of these habitats, such as the steppe connecting Alaska and Siberia, and the continental shelves off the north European coast, were very large. Animals and people were driven inland. The warming climate dried up the grassy Saharan savannahs and their rivers with crocodiles and hippopotami. It stranded a population of African elephants along the North African coast. This population of animals declined as the climate dried further and were hunted for ivory. The last of them may have become Hannibal’s elephants, led over the Alps to Rome. Such changes in climate reduced human habitat. The shifting climate resulted in deciduous forest covering much of temperate Asia, Europe and eastern North America. Much of this landscape had been steppe, or shrubby grassland with clumps of trees, inhabited by herds of horses, bison, elephants and reindeer, and by bands of human hunters. Productivity in the oceans, and in tropical forests, both limited by a lack of iron, shifted, as changes in atmospheric circulation patterns meant new winds carried iron-rich dusts from newly dry environments to new places. Expansion and contraction of the Amazon rainforest is thought to be partly caused by the supply of Saharan dust. Changes that cause a northern movement of the Intertropical Convergence Zone bring the summer monsoon from the Indian Ocean north and increase rainfall in the Sahara Desert; southward movement dries the desert. Very small changes in rainfall make the desert expand or contract. The Sahara was very dry during the late Ice Age, about 20,000 to 15,000 years ago. The Sahara grew wetter about 11,000 years ago as the glaciers melted, then began drying about 5500 years ago. At this time the rock paintings on desert walls changed from buffalo, crocodiles and elephants to small Saharan cattle, apparently newly domesticated: perhaps domesticated because of the growing drought.

So agriculture began during a time of rapid climate change. It didn’t begin in the Middle East. It began worldwide, about 10,000 years ago, with people growing plants in many different places. We Westerners, living in an era of unlimited fossil fuels, and with an extremely progressive view of history (a product of our material lives), see no mystery in this. Agriculture pointed the way out of the cave. Agriculture gave people more apparent control over their environment, through a more intensive manipulation of it, and thus more control over their lives; it made possible a sedentary life with permanent dwellings, easily storable foods, tools, clothes, beer, cooking utensils, decorative objects; more children. Agriculture can support many more people than hunting and gathering. Modern calculations indicate that solar-powered agriculture, with field work performed by men and animals, can support 64 to 256 people per square kilometer; in warmer, wetter climates multicropping is possible and the potential population doubles. Gathering and hunting can support up to 4 people per square kilometer (this is a low estimate). The worldwide average density of hunter-gathers is 1 person per 26 square kilometers (about 0.04 people per square kilometer). Most hunter-gatherers live at 20-60% of the calculated maximum carrying capacity of their environments; this may indicate their environments’ actual ability to provide continual subsistence. Similarly, wolves in Yellowstone keep elk at 20-30% below what the weather, through its effect on vegetation, would support; and thus create a more stable elk population.

With dense populations of sedentary agriculturalists, the arts bloomed: pottery-making, metal-working, tile-making, wall decoration. Many of these arts were heavy users of fuel. Mathematics, architecture, astronomy, and writing advanced along with larger, more complex, and more hierarchical societies; societies with hereditary classes of rulers, priests, warriors, artisans, farmers. Growing agricultural surpluses, that is, more excess production per farmer (as in Egypt, where a peasant produced five times the food required by his family), made possible the support of the non-farming classes. War was a sort of investment policy; a means of adding to the city’s wealth. War brought wealth through tribute and booty: in most premodern societies it is thought wealth came more from either increasing a group’s lands or war than from technological innovation. Behind all this was population growth. One of the effects of settled life is more frequent childbirth. A mother who moves camp every few days or weeks cannot deal with more than one non-ambulatory child. Some anthropologists think that nursing, which helps inhibit ovulation, went on for 4 to 6 years in a normal, that is, a gathering and hunting, society. (Gathering and hunting is by far the longest human adaptation.) At any rate, births tended to be spaced every 4 to 6 years. In an agricultural population births are limited mostly by the food supply and tend to come every 2 years. So populations began to rise. And as long as people were willing to work more, and more land was available, as long as the rains came, or the rivers rose and fell in a predictable way, agriculture would continue to feed many more people (ten to a hundred times more) per unit of land. In Neolithic Europe an agriculture of cattle, goats and hoe-cultivated wheat is thought to have supported 1 person per 120 hectares (50 acres), or about 8 per square kilometer (13 per square mile), twice that of the acorns and salmon of northern California. Most of the land was needed for browse for the animals. In Mesopotamia, cultivated land supported 100 or more people per square kilometer. (The population may have reached 20 million, with two-thirds of its 35,000 square miles of arable land irrigated, before the collapse.) A larger population is always the aim of biological evolution, and in human society, as in wolf society, numbers matter: the larger group wins the competition for resources. More resources allow the population to grow further. (Of course, technology can compound this.) Some anthropologists think the advantage of being able to mobilize people for war explains the development of agricultural chiefdoms and early states.

But none of this would have been apparent to people who harvested a few baskets of wild wheat, spilling some as they cut it down and carried it home (thus fulfilling the dispersal strategy of the wheat plant); or planted a hill of gourds (useful as containers) at a campsite to which they were likely to return in three months. Gathered wild grains may have been special foods at first, used for feasts, or to make beer. (Fruit-eating animals like elephants, American robins and people have a long acquaintance with fermentation, which is one way fruits attract attention—and explains those robins flying into autumn windows—but standard histories put the fermentation of beer several thousand years after the cultivation of grains.) The advantages of agriculture come at a later stage when people have, voluntarily or not, gathered into villages, when populations are denser, and agriculture is providing 90% or more of dietary calories. With the advantages of agriculture comes a down side: starvation, disease, more hierarchical societies, poorer health. The poorer diet, mostly of grains, expresses itself in shorter stature (the height of men may have fallen 6 inches, of women 5); in nutritional diseases like anemia and osteoporosis; in vitamin deficiencies; in overall poor health. Death comes earlier than among many of the gatherers, perhaps at 19 years in early agricultural societies, compared with 26 in groups of hunter-gatherers. (Such figures are disputed and vary. Cistercian monks in the 1300s died at an average age of 35, but it isn’t clear this figure takes into account a childhood mortality of 25-30%.) The heavy manual labor of agriculture causes degenerative skeletal diseases. Infectious diseases become more of a problem, partly because of the crowding, partly because of close contact with domestic animals, who are reservoirs of diseases that directly infect or adapt to humans. About 50 diseases are shared with cattle (including smallpox, measles, tuberculosis, and diptheria), 65 with dogs (our oldest companion), 46 with sheep and goats, 42 with pigs (including flu), some with birds (other flus), a few with horses (perhaps the common cold). Drinking water contaminated with human wastes spreads cholera, dysentery, and intestinal parasites. The parasitical diseases schistosomiasis and malaria are associated with irrigation in warm climates.

One scenario for the development of agriculture in the Middle East involves the Natufian people of present-day Israel and Jordan. About 15,000 years ago the Natufians lived on wild acorns and pistacios and hunted gazelles and wild sheep, in a landscape managed by burning. Their permanent villages were made possible by the abundant acorn crop, itself a consequence of more rainfall in the eastern Mediterranean with the retreat of the glaciers north. They also collected wild grains (wheat and two kinds of rye); these large-seeded grains returned a lot of food energy for the effort exerted in their harvest. The shutting down of the Gulf Stream between 13,500 and 12,600 years ago during the Younger Dryas Event (the result of the draining of a glacial lake in the center of North America into the Labrador Sea), caused temperatures to fall in northern Europe and a thousand year drought in southwest Asia. The acorn and pistachio crops collapsed. The Natufians, already living in villages, began cultivating cereals and keeping domestic animals. Large-seeded annual grasses such as wheat, emmer wheat and rye already formed large natural stands in their area. (In the 1960s, botanists found wild grains growing in more or less pure stands over hundreds of hectares in the same area.) The domestication of grains like wheat involves selection for plants that don’t drop their seeds when harvested, and whose seeds will sprout simultaneously when planted. It is thought the domestication of emmer wheat would have been rapid, taking 20 to 100 years, not several thousand, as with maize. (Emmer wheat is a natural hybrid of two grasses that occurred in the Near East 30,000 years ago. Bread wheat is a hybrid of emmer wheat with another grass that occurred 10,000 years later, at least 8,000 years before bread wheat was cultivated.) When warming resumed in Europe and rainfall improved in the eastern Mediterranean, farming and the keeping of domestic animals had taken hold; the villages had become larger. A later drying of the climate in the Near East, which made the growing of rainfed winter grains difficult, is thought to have led to the development of irrigation agriculture.

At some point an agricultural population outgrows its supply of wild game and gathered foods. Then return to an earlier way of life is not possible. (When their populations were still small and harvests were bad, the Anasazi, like the Pueblo people that survived them, made up the difference with wild grass seeds and pinion nuts; later, their population was too large and their landscape too altered for such foods to help.) In general, as populations grow, domestic animals, kept for meat, milk, fat, hides and traction power, are pastured on the stubble fields and in the surrounding wasteland, increasing the pressure on the local environment. Crafts such as pottery and metal-working require fuel, buildings need timber, grains must be cooked, and so trees become scarce and distant. Grazing prevents the re-establishment of forests cut for timber and fuel. As forests disappear, small streams dry up, floods increase, the land erodes, rivers grow more salty. Farmlands yield less, under continuous crops of grain. Crops also sometimes fail, and as the population grows, the threat of starvation becomes more constant. Unforseen or unmanagable environmental problems appear, sometimes the consequence of greater environmental manipulation, sometimes the result of natural disasters or of natural shifts in climate. Populations near the carrying capacity of their environments make collapse of the civilization more likely. Past problems include soil erosion about the Mediterranean basin and in upland Mesopotamia; too great or too low floods in Egypt; the slow saltation of irrigated lands in lowland Mesopotamia (these lands, like those in the American Southwest, require a long fallow to avoid saltation and waterlogging); droughts in the Andes, and in the Mayan highlands; a tectonically mediated rise in the water table along the lower Indus River that flooded the foundations of the city of Mohenjo-Daro, and required the firing of more and more brick to build the buildings up, with more and more wood cut from the drying jungle; the “dry fog” in 535 AD (from a volcanic eruption? an exploding comet?) that cooled the climate and caused crop failure and famine in Europe, southwest Asia and China. Trade, perhaps allied with weather conditions, such as the warm, wet spring weather that increases the presence of bubonic plague in the marmots of the Asian steppe, introduces new diseases, to which populations are not adapted. Rome suffered from several plagues in the years after 144 AD, at a time when a warmer, dryer climate in the southern and eastern Mediterranean and in North Africa was disrupting its agricultural base. By then the conquests that had made the early empire wealthy no longer paid their costs. (The lightly settled northern lands lacked the wealth of the older Mediterranean cultures that were first taken over.) From the first century on, the tax base of the empire was largely agricultural. Taxes, though heavy, fell short of paying the costs of administration and defense became more and more difficult. The population never recovered from the plagues of the second century. The plague of Justinian that started in 542 AD may have killed half the people in the empire. In an overpopulated society disasters and epidemics could be an economic blessing. The Black Death, which is thought to have killed a third to a half of the population of Europe from 1347-1349, was followed by a century of recurrent epidemics of diseases with severe mortalities (plague, smallpox, flu, dysentery), along with some episodes of starvation, so that in 1450 the population of Europe was probably half that of 1347. (Without the additional epidemics, the population would have recovered in 30 years. The population of China, which was affected by the Black Death earlier, also fell by half from 1200 to 1400.) The depopulation of Europe gave a considerable push to the economic expansion of the Renaissance. Poor farmland was abandoned, so crop yields rose. Food became more abundant, labor scarcer, wages higher (50% higher in Florence, compared with 50 years before); the poor gained wealth and bargaining power, which led to the peasant revolts of the late 1300s and the gradual erosion of serfdom. Technological innovation grew. Much wealth was transferred from the dying, some of it to the new European universities. In England, land without heirs went to the local nobility, who grew richer, and also financed development schemes, such as mines and the reclamation of waste land for agriculture. In general, the landed gentry lost wealth and power compared to the laboring classes. Depopulation resulted in a more diversified, more capital intensive, more technologically advanced economy, and a more prosperous population.