THE GLOBAL AGRICULTURAL REVOLUTION

Southwest Asia: Cereals and Mammals

The first agricultural revolution occurred in Southwest Asia in an area bounded by the Mediterranean Sea and the Zagros Mountains. Because of its rich soils and regular rainfall, this area played a leading role in the domestication of wild grasses and the taming of animals important to humans. Six large mammals—goats, sheep, pigs, cattle, camels, and horses—have been vital for meat, milk, skins (including hair), and transportation. Southwest Asians domesticated all of these except horses.

Around 9000 BCE, in the southern corridor of the Jordan River valley, humans began to domesticate the wild ancestors of barley and wheat. (See Map 1.5.) Various wild grasses were abundant in this region, and barley and wheat were the easiest to adapt to settled agriculture and the easiest to transport. Although the changeover from gathering wild cereals to regular cultivation took several centuries and saw failures as well as successes, by the end of the ninth millennium BCE, cultivators were selecting and storing seeds and then sowing them in prepared seedbeds. Moreover, in the valleys of the Zagros Mountains on the eastern side of the Fertile Crescent, similar experimentation was occurring with animals around the same time.

East Asia: Rice and Water

A revolution in food production also occurred among the coastal dwellers in East Asia, although under different circumstances. (See Map 1.6.) Throughout this region, the spread of lakes, marshes, and rivers created habitats for population concentrations and agricultural cultivation. Two newly formed river basins became densely populated areas that were focal points for intensive agricultural development. These were the Yellow River, which deposited the fertile soil that created the North China plain, and the Yangzi River, which fed a land of streams and lakes in central China.

Rice in the south and millet in the north were for East Asia what barley and wheat were for Southwest Asia—staples adapted to local environments that humans could domesticate to support a large, sedentary population. Archaeologists have found evidence of rice cultivation in the Yangzi River valley in 6500 BCE and of millet cultivation in the Yellow River valley in 5500 BCE. Innovations in grain production spread through internal migration and wider contacts. When farmers migrated east and south, they carried domesticated millet and rice. In the south, they encountered strains of faster-ripening rice (originally from Southeast Asia), which they adopted. Rice was a staple in wetter South China, but millet and wheat (which spread to drier North China from Southwest Asia) were also fundamental to the food-producing revolution in East Asia.

Africa: The Race with the Sahara

The evidence for settled agriculture in the various regions of Africa is less clear. Most scholars think that the Sahel area (spanning the African landmass just south of the Sahara Desert) was likely where hunters and gatherers became settled farmers and herders without any borrowing. In this area, an apparent move to settled agriculture, including the domestication of large herd animals, occurred two millennia before it did along the Mediterranean coast in North Africa. From this innovative heartland, Africans carried their agricultural breakthroughs across the landmass.

It was in the wetter and more temperate locations of the vast Sahel, particularly in mountainous areas and their foothills, that villages and towns developed. These regions were lush with grassland vegetation and teeming with animals. Before long, the inhabitants had made sorghum, a cereal grass, their principal food crop. Residents constructed stone dwellings, underground wells, and grain storage areas. In one such population center, fourteen circular houses faced each other to form a main thoroughfare, or street. Archaeological investigations have unearthed remarkable rock engravings and paintings, often one composed on top of another, filling the cave dwellings’ walls. Many images portray in fascinating detail the changeover from hunting and gathering to pastoralism. Caves abound with pictures of cattle, which were a mainstay of these early men and women. The cave illustrations also depict daily activities of men and women living in conical huts, doing household chores, crushing grain on stone, and riding bareback on oxen (with women always sitting behind the men, potentially an early example of male superiority in some African societies).

The Sahel was colder and moister 10,000 years ago than it is today. As the world became warmer and the Sahara Desert expanded, around 4,000 years ago, this region’s inhabitants had to disperse and take their agricultural and herding skills into other parts of Africa. (See Map 1.7.) Some went south to the tropical rain forests of West Africa, while others trekked eastward into the Ethiopian highlands. In their new environments, farmers searched for new crops to domesticate. The rain forests of West Africa yielded root crops, particularly the yam and cocoyam, both of which became the principal life-sustaining foodstuffs. The ensete plant, similar to the banana, played the same role in the Ethiopian highlands. Thus, the beginnings of agriculture in Africa involved both innovation and diffusion.

The Americas: A Slower Transition to Agriculture

The shift to settled agriculture occurred more slowly in the Americas. When people entered the Americas around 16,000 years ago (14,000 BCE), they set off an ecological transformation but also adapted to unfamiliar habitats. The flora and fauna of the Americas were different enough to induce the early settlers to devise ways of living that distinguished them from their ancestors in Afro-Eurasia. Then, when the glaciers began to melt around 12,500 BCE and water began to cover the land bridge between East Asia and America, the Americas and their peoples truly became a world apart.

CLIMATIC CHANGE AND ADAPTATION The traditional narrative has been that early humans in America, called “Clovis people” after an archaeological site near Clovis, New Mexico (dating to around 11,000 BCE), used chipped blades and pointed spears to pursue their prey. New excavations, however, are unearthing even earlier evidence for human occupation in the Americas, with “pre-Clovis” sites ranging from Idaho to Pennsylvania and the southeastern United States to Brazil and Chile. (See Map 1.2 for the complicated picture of human migration in the Americas.) Although scientists once thought that early hunting and gathering communities in the Americas had wiped out the large ice-age mammals in the Americas, recent research suggests that climatic change destroyed indigenous plants and trees—the feeding grounds of large prehistoric mammals. This left undernourished mastodons, woolly mammoths, bison, and other mammals vulnerable to human and animal predators. As in Afro-Eurasia, the arrival of a long warming cycle compelled those living in the Americas to adapt to different environments and to create new ways to support themselves. Thus, in the woodland area of the present-day northeastern United States, hunters learned to trap smaller wild animals for food and furs. To supplement the protein from meat and fish, these people also dug for roots and gathered berries. Even as most communities adapted to the settled agricultural economy, they did not abandon basic survival strategies of hunting and gathering.

Food-producing changes in the Americas were different from those in Afro-Eurasia because the Americas did not undergo the sudden cluster of innovations that revolutionized agriculture in Southwest Asia and elsewhere. Tools ground from stone, rather than chipped implements, appeared in the Tehuacán Valley in present-day eastern central Mexico by 6700 BCE, and evidence of plant domestication there dates back to 5000 BCE. But villages, pottery making, and sustained population growth came later. For many early American inhabitants, the life of hunting, trapping, and fishing went on as it had for millennia.

On the coast of what is now Peru, people found food by fishing and by gathering shellfish from the Pacific. Archaeological remains include the remnants of fishnets, bags, baskets, and textile implements; gourds for carrying water; stone knives, choppers, and scrapers; and bone awls (long, pointed spikes often used for piercing) and thorn needles. Thousands of villages likely dotted the seashores and riverbanks of the Americas. Some communities made breakthroughs in the management of fire, which enabled them to manufacture pottery; others devised irrigation and water sluices in floodplains; and some even began to send their fish catches inland in return for agricultural produce.

DOMESTICATION OF PLANTS AND ANIMALS The earliest evidence of plant experimentation in Mesoamerica (the region now known as Mexico and Central America) dates from around 8000 BCE, and it went on for a long time. Maize (corn), squash, and beans (first found in what is now central Mexico) became dietary staples. The early settlers foraged small seeds of maize, peeled them from ears only a few inches long, and planted them. Maize offered real advantages because it was easy to store, relatively imperishable, nutritious, and easy to cultivate alongside other plants. Nonetheless, it took 5,000 years for farmers to complete its domestication. Over the years, farmers had to mix and breed different strains of maize for the crop to evolve from thin spikes of seeds to cobs rich with kernels, with a single plant yielding big, thick ears to feed a growing permanent population. Thus, the agricultural changes afoot in Mesoamerica were slow and late in maturing. The pace was even more gradual in South America, where early settlers clung to their hunting and gathering traditions.

Across the Americas, the settled, agrarian communities found that legumes (beans), grains (maize), and tubers (potatoes) complemented one another in keeping the soil fertile and offering a balanced diet. Unlike the Afro-Eurasians, however, the settlers did not use domesticated animals as an alternative source of protein. In only a few pockets of the Andean highlands is there evidence of the domestication of tiny guinea pigs, which may have been tasty but unfulfilling meals. Nor did people in the Americas tame animals that could protect villages (as dogs did in Afro-Eurasia) or carry heavy loads over long distances (as cattle and horses did in Afro-Eurasia). Although llamas could haul heavy loads, they were uncooperative and only partially domesticated, and thus mainly useful only for their fur, which was used for clothing.

Nonetheless, the domestication of plants and animals in the Americas, as well as the presence of villages and clans, suggests significant diversification and refinement of technique. At the same time, the centers of such activity were many, scattered, and more isolated than those in Afro-Eurasia—and thus more narrowly adapted to local geographical climatic conditions, with little exchange between communities. This fragmentation in migration and communication was a distinguishing force in the gradual pace of change in the Americas, and it contributed to their taking a path of development separate from Afro-Eurasia’s.

Europe: Borrowing Agricultural Ideas

In some places, agricultural revolutions occurred through the borrowing of ideas from neighboring regions, rather than through innovation. Peoples living at the western fringe of Afro-Eurasia, in Europe, learned the techniques of settled agriculture through contact with other regions.

By 7000 BCE, people in regions of Europe close to the societies of Southwest Asia, such as those living in what are modern-day Greece and the Balkans, abandoned their hunting and gathering lifeways to become settled agriculturists. (See Map 1.8.) Places like the Franchthi Cave, in Greece, reveal that around 6000 BCE the inhabitants borrowed innovations from their neighbors in Southwest Asia, such as methods for herding domesticated animals and planting wheat and barley. From the Aegean and Greece, settled agriculture and domesticated animals expanded westward throughout Europe, accompanied by the development of settled communities.

The emergence of agriculture and village life occurred in Europe along two separate paths. The first and most rapid trajectory followed the northern rim of the Mediterranean Sea. Domestication of crops and animals moved westward, following the prevailing currents of the Mediterranean, from what is now Turkey through the islands of the Aegean Sea to mainland Greece, and from there to southern and central Italy and Sicily. Once the basic elements of domestication had arrived in the Mediterranean region, the speed and ease of seaborne communications aided astonishingly rapid changes. Almost overnight, hunting and gathering gave way to domesticated agriculture and herding.

The second trajectory took an overland route: from Anatolia, across northern Greece into the Balkans, then northwestward along the Danube River into the Hungarian plain, and from there farther north and west into the Rhine River valley in modern-day Germany. Change here likely resulted from the transmission of ideas rather than from population migrations, for community after community adopted domesticated plants and animals and the new mode of life. This route of agricultural development was slower than the Mediterranean route for two reasons. First, domesticated crops, or individuals who knew about them, had to travel by land, as there were few large rivers like the Danube. Second, it was necessary to find new groups of domesticated plants and animals that could flourish in the colder and more forested lands of central Europe. Agriculturalists here had to plant their crops in the spring and harvest in the autumn, rather than the other way around. Cattle rather than sheep became the dominant herd animals.

In Europe, the main cereal crops were wheat and barley, and the main herd animals were sheep, goats, and cattle—all of which had been domesticated in Southwest Asia. (Residents domesticated additional plants, such as olives, later.) These fundamental changes did not bring dramatic material progress, however. The typical settlement in Europe at this time consisted of a few dozen mud huts. These settlements, although few, often comprised large “long houses” built of timber and mud, designed to store produce and to shelter animals during the long winters. Some settlements had sixty to seventy huts—in rare cases, up to a hundred. Hunting, gathering, and fishing still supplemented the new settled agriculture and the herding of domesticated animals. The innovators were dynamic in blending the new ways with the old. Consider that around 6000 BCE, hunters and gatherers in southern France adopted the herding of domesticated sheep, but not the planting of domesticated crops—that would have conflicted with their preference for a life of hunting, which was a traditional part of their economy.

By about 5000–4000 BCE, communities living in areas around rivers and in the large plains had embraced the new food-producing economy. Elsewhere (notably in the rugged mountain lands that still predominate in Europe’s landscape), hunting and foraging remained humans’ primary way of subsisting. Thus, across Afro-Eurasia, humans changed and were changed by their environments. While hunting and gathering remained firmly entrenched as a way of life, certain areas with favorable climates and plants and animals that could be domesticated began to establish settled agricultural communities, which were able to support larger populations than hunting and gathering could sustain.

The Environmental Impact of the Agricultural Revolution and Herding

From the moment humans began to farm and herd on a large scale, they began to have a warming effect on the climate. The burning of forests, the cultivation of the major grain crops, and the amassing of large herds of domesticated animals caused methane and carbon dioxide (today called greenhouse gases) to escape from the earth and be trapped in the earth’s atmosphere. As a result, cooling cycles that occurred as the earth tilted away from the sun were not as severe as they would have been. Of course, it was only in the last 200 years that these gases have caused the severe warming of the planet that threatens our planet’s existence.