The Natural History of the Present, Chapter 9

Chapter 9: Were Ancient Marketable Landscapes Sustainable?

Westerners are taught that civilization began in the Fertile Crescent of Mesopotamia. This is a matter of cultural focus, for while agricultural civilization reached a more extensive development in Eurasia at an earlier time, agricultural development elsewhere began not much later and eventually reached comparable levels. But those agricultural civilizations (say, in the Americas, or in highland New Guinea) did not lead in a straight line to the modern West. Rather they were all taken over by that bellicose, capitalist, Christian culture that rose in Europe over some 1500 years out of its Mediterranean and Near Eastern roots.

In Mesopotamia, the adoption of agriculture seems more obvious than in many places. Wild annuals like emmer wheat and barley grew in large natural stands; for wild crops, they were exceptionally large-seeded. These plants formed a natural climax in the wet winters and long dry summers of the eastern Mediterranean, in micro-climates where the length of the summer drought made the support of woody vegetation difficult. Especially on fertile sites, these tall annuals grew quickly and used up the available soil moisture, preventing percolation and out-competing trees and shrubs. Their seeds were adapted to survive the long summers and sprout and grow quickly in the returning winter rains. A ton of seeds per hectare could be gathered with a hand sickle from such wild stands. The warming and drying climate at the end of the Pleistocene greatly expanded the range of these plants altitudinally. People could harvest them from month to month as summer proceded up the mountain terraces, and store the surplus. The Middle East also had many other of the wild precursors of modern crops, especially the pulses (the protein-rich lentils, peas, chick-peas and bitter vetch); and also flax, whose stems produced a fiber and whose seeds produced an edible oil. Combining grains and pulses in a dish produces so-called complementary proteins, a mix of proteins that corresponds more closely to what the human body needs—not as good as animal protein, but much better than grains alone: so one has wheat and chickpeas, rice and beans, beans and corn. (Chickpeas also contain tryptofan, a precursor of serotonin, which improves performance under stress and promotes ovulation.) Wild cows, sheep, pigs and goats also lived in the area; animals that were domesticable because of their tractable natures and herding or flocking behaviors. (Other crops soon included barley, oats, grapes, olives, dates, figs, apples, pears and cherries.) So here one can more easily envision how an increased birth rate, thanks to a more sedentary life based on acorns and pistacios, and also on gathered cereals and pulses, carried down to the village in woven woolen bags lashed over the backs of goats and sheep, led to an upward population spiral that then led to more settled agricultural communities: permanent fields, domestic animals (pastured after harvest on the fields), stone or mud-brick dwellings, pottery-making. Such villages, based on hoe culture of grain and on domestic animals, existed in upland Mesopotamia 9000 years ago in areas with sufficient rainfall. By 8000 years ago, in what is now central Jordan, such communities were being abandoned, partly because of soil exhaustion and deforestation, and partly because of a drought associated with another breakdown in the North Atlantic circulation, this one caused by the final meltdown of the Laurentide Glacier in North America. With the end of that drought about 7000 years ago, Europe entered a climatic optimum that lasted 2000 years.

The progression to agriculture is less obvious elsewhere. In eastern North America the Hopewell mound-builders of the Ohio and Illinois valleys were cultivating seven crops about 2500 years ago. Four of them were grains with tiny seeds but good protein and fat content; the other crops were a squash and a sunflower grown for their seeds, and sumpweed, a large oilseed, whose pollen and leaves are often irritating to people. These crops were grown on the floodplains of the rivers after the flood had receded. While seed crops provided a considerable part of the diet, the people in the Hopewell cities also ate fish, shellfish, deer, migratory waterfowl, turtles, passenger pigeons, and wild nuts. They have been called cities of hunters and gatherers. (Cahokia, a later mound-building city near present-day St. Louis, was based on maize. Cahokia was a city of several thousand small farms, apparently without significant trading relations with other places.) Shellfish were very abundant in Middle Western rivers. Nuts and acorns had been important foods for people dwelling in the mesic forests of eastern North America for thousands of years. Most acorns have to be leached of their tannins to be edible. Hickory nuts were pounded shell and all in a mortar, the mass boiled in water, and skimmed of froth and particles of shell. Further boiling reduced the mass to a nutritious, storable paste: hickory milk. In the late 1700s John Bartram watched Creek families in North Carolina store hundreds of bushels of hickory nuts. While corn would transform life in aboriginal North America, the domestication of corn in highland Mexico took thousands of years. The plant that became corn was grown for several thousand years before its seeds became usable as a grain. Corn may have been first grown for its sweet stalks, fermented to make beer. (Modern maize stalks are 16% sugar.) An entire ear of Teosinte, the plant that was turned into corn by generations of middle American women, has less nutritional value than one kernal of modern maize. It took many more years for corn to change its daylength characteristics from tropical to temperate and move north. The advantages of corn over the native domesticates were immediately apparent, and when corn appeared, the tribes adopted it. Corn changed social structures; many societies became more hierarchical and their villages larger. In the Asian subtropics, the cultivation of paddy rice involved the invention of a method of cultivation. The method is not obvious. (The cultivation of upland rice is another matter.) In these cases the immediate advantages of agriculture were more difficult to see, and the process that led to a settled agricultural life more difficult to imagine.

In the Near East, irrigation societies and large cities (50,000 people and up), with their organized hierarchies of nobles, priests, courtiers, warriors, artisans and farmers; their massive public buildings of brick, mud-brick or stone; their calenders based on astronomical observation; their use of writing; and war for the purpose of gaining land and tribute, developed after some thousands of years of upland village agriculture. Early cities were storehouses for grain: a means of distributing food, trading for it, and storing it against a risk of crop failure. (One can regard modern cities as means of maintaining and distributing wealth.) These societies exploited a new environment: the flat and arid Mesopotamian plain, with its high summer temperatures (40º C., 104º F.), high evaporation rates and relatively impermeable soils. Initially agriculture here consisted of the cultivation of rainfed winter grains, but the shift of the Indian monsoon south about 5800 years ago reduced winter rainfall so that winter crops would no longer grow. The timing of high water meant that irrigated crops would have to be grown in the hot summer. So more water was needed and soils accumulated salts more quickly. Irrigation produced a more apparently controllable supply of water than rain (it depended on the reliabability of the river’s flow patterns), and a much larger harvest per unit of land. The agricultural work was seasonal. In the off seasons, farmers could extend and maintain the irrigation system. Thus the surplus per farmer was considerably more and the other levels of the society considerably richer than in the upstream societies that still depended on rainfed agriculture. Irrigation also made large areas of new land cultivable.

The Tigris and Euphrates took parallel courses across the Mesopotamian plain, but at slightly different elevations. The plain was essentially flat; the rivers dropped 30 meters over a distance of 700 kilometers. Overflow channels connected the rivers during spring floods, and the first irrigation schemes exploited these channels. The land between the rivers was a mix of swamps, stands of date palms, forest, shrubs and grassland. Large herds of gazelle, along with other herbivores and their feline and canine predators, originally occupied the plain. The Euphrates carried a lot of silt; its delta moved out into the Persian Gulf at 15 miles per 1000 years, so ancient trading cities near the gulf are now 50 to 70 miles inland. Irrigation agriculture would have had all the disadvantages of rainfed agriculture: a poorer diet (with sufficient calories, but less balanced, with less protein, and less calcium, potassium, and other minerals and vitamins, and thus leading to poorer overall health, more skeletal disease and shorter stature); the diseases and parasites that come from contact with water containing human excreta (various worms, including those that cause schistosomiasis), and those that come from close contact with domestic animals (many of the latter are also crowd diseases that require a sufficient density of human population to maintain themselves and so flourish in cities); the skeletal problems caused by hard physical labor; and earlier death. But at least at first, some of these irrigation societies were rich and grew a wide variety of crops, including pulses and some vegetables and fruits (such as onions and figs, sources of sugars, minerals and vitamins). Animal protein came from herds of goats and sheep that were pastured out on the plains in summer, along the rivers in winter. Wooden rafts supported by inflatable goatskins brought commodities down the Tigris in summer. Timber from the rafts and the commodities, including semi-precious stones and copper, were sold, and the goatskins packed back upstream. The actual extent of nutritional diseases would have depended on how well food was distributed; of waterborn diseases on the city’s organization of things like water supply and sanitation (whether drinking water and human excreta were separated). That is to say, depending on the political situation (the extent to which the needs of the people were taken into account), the jump in agricultural productivity associated with irrigation agriculture might have let these peoples raise their general levels of health (as well as raise the standard of living of their elites), at least for some time.

There were the usual advantages of agricultural societies: a higher birth rate and higher population; permanent dwellings; fine and varied craft work; the development of the sciences of mathematics, engineering and astronomy; the construction of large public buildings; improved methods of war; and writing. In the several times writing has been invented (Sumeria; Mexico; perhaps Egypt; probably China; perhaps Peru) it always flowed from irrigation, or quasi-irrigation, societies. Sumerians seem to have invented writing first, part of the great head start of Eurasia in cultural evolution. This was a gift of geography and biology, as a modern writer has explained. The easily domesticated plants and animals of southwest Asia could be grown without much adaptation north and west through Europe and east through much of Asia, an immense area, which led to societies influencing each other with ideas, new crops, new inventions; thus cultural development was rapid. Writing in Sumeria began, like the knotted strings of the Inca, from the need to keep agricultural accounts. By making possible the recording of knowledge (as well as that of wealth) writing made possible the accumulation of knowledge (in mathematics, biology, astronomy, physics, law, natural history, human history); that is, it made possible the modern world.

Irrigation societies in Mesopotamia would all eventually collapse because of the character of the landscape’s soils and the climate. Failure through saltation, accumulation of toxic minerals, or waterlogging is the fate of virtually all large-scale irrigation schemes in hot, dry climates. The muddy waters of the Tigris and Euphrates had a relatively high salt content. This was partly natural, partly the result of some thousands of years of agricultural erosion and deforestation upstream. The high summer temperatures of the Mesopotamian Plain meant a high rate of evaporation and of water use. The time of spring high water meant that crops, unlike the rainfed grains of the Mediterranean uplands or those in Egypt, where the Nile flood arrived in early autumn, allowing for a late autumn sowing, were grown in the summer heat. Thus they required a lot of water. The high salt content of the water and the relatively impermeable soils meant that the soils would inevitably begin to accumulate salt. Salt interferes with the ability of plants to take up water and thus reduces their growth. This soon became apparent and new land was brought into cultivation as the fertility of the old fields fell. (Modern irrigation schemes in impermeable soils sometimes solve this problem by installing drains to carry away the excess water.) The development of new lands maintained total agricultural productivity and accomodated the rising population for a long time. But the climatic drying that began 5800 years ago continued. As new land ran out, and population pressure prevented the use of long-term fallows, crops in Sumeria shifted from wheat to the more salt-tolerant barley. The cities also needed wood, which had to be within an economical hauling distance (some came down the Tigris in rafts), to smelt metal, fire pottery, brew beer, burn brick, cook the pulses and grains, and for building material. Deforestation added to the salts and silt carried by the river water. The irrigators kept cows, pigs, chickens, and goats, and so the cutover forests were grazed, which prevented their regrowth. Such use slowly transformed the whole landscape within the reach of the Sumerian cities and intensified the load of silts and salts that fed the rivers. Rising silt loads made keeping the canals open a constant problem, and sent the Euphrates migrating across its plain. Such problems take time to develop on a large scale, but unless dealt with, become (like our rising curve of carbon dioxide) more and more inexorable in their effects. About 5500 years ago equal amounts of wheat and barley were grown in Sumeria, by 4500 years ago wheat amounted to 15% of the crop, by 4100 years ago 2%, by 3700 years ago no wheat was grown. Crop yields remained high until 4400 years ago —that is, for 1100 years, far longer than we have been growing industrial grain in the American Middle West. After 4400 years ago, no new land was available and crop yields fell by 40% over the next 300 years. From 4200 to 3900 years ago there was a region-wide drought. Egypt’s Old Kingdom collapsed about 4200 years ago. Water levels in the Euphrates may have fallen below the beds of the canals. The drought was so severe that in fields near the Syrian border the earthworms died. The first external conquest of the region occurred almost concurrently with the end of new land, 4375 years ago. By 3800 years ago yields were less than 20% those of earlier times and the society had effectively collapsed.

Sumerian agriculture might have been sustainable if it had been handled differently, using fields over a long rotation (like the Hohokum of the American Southwest). Some ancient irrigation agricultures were sustainable: Egypt’s; the Mayas’ ditched swamps; the raised beds of the Tiahuanaco; paddy rice in Asia; floodplain agriculture along the lower Mississippi or Amazon. None of these are irrigation agricultures in the classic sense. In the Nile Valley the flood was usually high enough, and the soils beneath were more permeable, so the water washed the salts from the flooded land. Agriculture along the Nile was a sort of improved floodplain agriculture, much like that along the Mississippi and the Amazon. In the swamps of the Maya and the raised fields of Tiahuanaco, the water percolated up from below. Paddy rice involves a constant slow flow over a more or less impenetrable substrate.

Until the building of the dam at Aswan, Egypt’s Nile Valley was probably the most naturally productive agricultural landscape in the world. When invaded by Napolean in the 1790s, Egypt’s wheat yields were twice those of France. By then the valley had been cultivated continuously for 7000 years. Half or more of Egypt’s cultivable land is in the delta. The geology of the lower Nile Valley and the use of its natural overflow basins for agriculture removed the problems of saltation and waterlogging. After the flood, the water table would drop 10 feet below the valley bottom, letting the flood waters drain away. The timing of the overflow also helped. Water from the spring rains in the uplands of east Africa (present-day Ethiopia and Uganda) reached the Nile Delta in September, so crops were sown in late fall and matured in the cooler temperatures of winter. Spring and summer irrigation was restricted by the available technology to areas near the river, which the floods would leach clean of salts every year. Fertility was provided annually by the silt, and also by human and animal manure. Fertilising minerals came with the river water from the highlands of Abyssinia, humus from the jungles of central Africa. As in Mesopotamia, the volume of silt may have been increased by deforestation for agriculture in Ethiopia and for metal smelting in the Ugandan uplands. But the river was also cleaned and regulated by its passage through the swamps of Nubia, before it fell to the lower valley. The Nile also provided fish, both in the river and off the delta. The nutrients and fresh water brought down by the Nile supported fisheries throughout the eastern Mediterranean. The problem with the Nile flood was its unpredictability. Low floods occurred about twice a decade. The heights of Nile floods are connected to El Nino Events, which influence the northward reach of the Indian Ocean monsoon, and thus the extent of spring rains in Ethiopia. Two low floods in a row were a disaster. A flood can also be too great, remaining on the land too long and preventing the sowing of the winter crops. So, loosely speaking, the agricultural area would have supported a population that could store sufficient grain for 2 years. But population control is not the point of high civilisations, the timing of low or high floods wasn’t predictable, and since Early Dynastic times the population kept rising above the food supply. Periodic starvation was common. Of course over such a long period of time Egypt also had more severe climatic disasters. The end of the Old Kingdom was caused by 300 years of low floods. A drought in the eastern Mediterranean 3200 years ago stressed all the civilizations of the area. It helped in the collapse of Mycenaen Crete, already half-destroyed by a tsunami from the volcanic eruption on Santorini. The earthquakes that accompanied the eruption apparently compromised the island’s aquifers. The Cretans traded olive oil and wine for grain from the mainland; they also grew some wheat themselves; the drought reduced their crops and meant less grain was available from the mainland. Even in this lucky landscape, the Egyptians were caught between the constant increase in the human population and the behavior of the river.

Paddy rice constitutes another sustainable agricultural system. Tropical soils in humid climates, once cleared of their natural vegetation, are in general impervious and nutrient poor. The soils are old, and have been depleted by rainfall, plant respiration, and internal erosion. Most of their nutrients are concentrated in the vegetation that is removed. In paddy rice cultivation, the nitrogen that feeds the rice plant comes largely from blue-green algae that colonize the warm, slowly moving water that covers the paddy. The water itself, descending from the uplands, provides some nutrients (phosphorus and other minerals). Trampling and working of the paddy bottom makes the soil more or less watertight, so water and nutrients are retained. Fish and freshwater invertebrates grow in the paddies and the feeder canals. In the Lake Biwa basin of Japan, very old paddy fields are used by the lake’s catfish as a spawning area and nursery: that is, as an extension of the lake itself. This use is a benefit both to the farmers, who harvest some of the fish and whose rice is more productive, and to the fish. In some cases the nutrient-rich overflow from the paddies is led to duck ponds, whose algal and insect life (food for the ducks) is supplemented by grain. The ponds, their bottom muds fertilized by the algal and bacterial growth and by that cycled through the ducks, are periodically drained and planted to vegetables. Fertility of the paddies is also maintained by adding manure from the animals that plow them, human manure, ashes, the walls of demolished mud-brick houses impregnated with soot and grease from cooking.

The water buffalo whose manure ends up on the paddy and increases its yield of rice, is fed from forage cut in the nearby forest. Irrigation water also comes from the forest. So the forest is part of the paddy system. It also provides firewood, small game, material for building and basketry. Lowland rice-growing systems, irrigated by large rivers, also depend on a predictable supply of good quality water. These systems can be overwhelmed by timber cutting in the watershed and the change in the quality, timing and amount of water delivered to the paddies that this causes.

So some agricultural systems of “high” civilizations were sustainable, some not; some landscapes could stand more human development, some less. Any human civilization is a outgrowth of an existing landscape and climate, that is, of levels of rainfall and temperature, of sea levels, flood levels, the likelihood of extreme weather events. All agricultural systems can be pushed over the edge by too much development about them or by small climatic changes. Increase in population is often the problem, though technology also matters, in that technology magnifies the effects of population. In the 1800s, perennial irrigation to grow cotton (three crops a year) began to salinize Egyptian fields. The building of the dam at Aswan, which cut off the natural flow of water and silt, turned the Nile Valley into an unsustainable agricultural system. Salinization is now a problem, the fishery for sardines off the delta has collapsed, and without a yearly influx of silt, the land in the delta is receding.