Figure 3. Map of the Middle East.

      The climate shift of the Younger Dryas was not the only factor that influenced the adoption of agriculture. Population growth during the preceding several thousand years led to the advent of sedentary communities of hunter-gatherers and contributed to the effect of this climate shift on human populations. Still, the starving people of Abu Hureyra could never have imagined that their attempt to adapt to a drying world would transform the planet.

      Such adaptation may have occurred around the region. The end of the Younger Dryas coincides with changes in culture and settlement patterns throughout much of the Middle East. Neolithic settlements that emerged after the Younger Dryas were located at sites ideally suited for agriculture with rich soils and ample water supplies. Charred remains of domesticated wheat dating from 10,000 years ago are found in sites near Damascus, in northwestern Jordan, and on the Middle Euphrates River. Domesticated crops then spread south to Jericho in the Jordan Valley and northwest into southern Turkey.

      Although tradition places agriculture in the Middle East long before any parallel activity in Asia and the Americas, recent research suggests that people in South America, Mexico, and China may have domesticated plants long before the first signs of settled villages in these regions. Sediments in a cave called Diaotonghuan along China's Yangtze River tell a story similar to that of Abu Hureyra in which wild rice was domesticated around the time of the Younger Dryas. Perhaps the abrupt climate changes of the Younger Dryas pushed semisettled people with declining resource bases into agricultural experimentation.

      Once the climate improved, groups adapted to growing grains had an advantage. Increasing reliance on domesticated crops spread across the region. The Natufian culture that flourished along the Mediterranean coast in modern Israel, Lebanon, and Syria from 9000 until 7500 BC was based on harvesting wild grain and herding goats and gazelles. Neither plants nor animals were fully domesticated when Natufian culture arose, yet by the end of the era, hunting accounted for just a fraction of the food supply.

      The regional population began to grow dramatically as domestication of wheat and legumes increased food production. By about 7000 BC small farming villages were scattered throughout the region. Communities became increasingly sedentary as intensive exploitation of small areas discouraged continuing the annual cycle of moving among hunting camps scattered around a large territory. By about 6500 BC large towns of up to several thousand people became common. The seasonal rhythm of an annual trek to follow resources was over in the Middle East.

      Populations able to wrest more food from their environment could better survive periods of stress—like droughts or extreme cold. When bad times came, as they inevitably did, chance favored groups with experience tending gardens. They better endured hardships and prospered during good times. And agricultural success upped the ante. Development of more intensive and effective subsistence methods allowed human populations to grow beyond what could be supported by hunting and gathering. Eventually, communities came to depend on enhancing the productivity of natural ecosystems just to stay even, let alone grow. Early cultivators became tied to a place because mobility did not allow for tending and harvesting crops. Once humanity started down the agricultural road there was no turning back.

      Learning to support more people on less land once they settled into a region, farmers could always marshal greater numbers to defeat foragers in contests over territory. As their numbers grew farmers became unbeatable on their own turf. Field by field, farms expanded to cover as much of the land as could be worked with the technology of the day.

      Most farm animals were domesticated from about 10,000 to 6000 BC. My favorite exception, the dog, was brought into the human fold more than twenty thousand years earlier. I can easily imagine the scenario in which a young wolf or orphaned puppies would submit to human rule and join a pack of human hunters. Watching dogs run in Seattle's off-leash parks, I see how hunters could use dogs as partners in the hunt, especially the ones that habitually turn prey back toward the pack. In any case, dogs were not domesticated for direct consumption. There is no evidence that early people ate their first animal allies. Instead, dogs increased human hunting efficiency and probably served as sentries in early hunting camps. (Cats were relative latecomers, as they moved into agricultural settlements roughly four thousand years ago, soon after towns first overlapped with their range. As people settled their habitat, cats faced a simple choice: starve, go somewhere else, or find food in the towns. No doubt early farmers appreciated cats less for their social skills than for their ability to catch the small mammals that ate stored grain.)

      Sheep were domesticated for direct consumption and economic exploitation sometime around 8000 BC, several hundred years before domestication of wheat and barley. Goats were domesticated at about the same time in the Zagros Mountains of western Iran. It is possible that seeds for the earliest of these crops were gathered to grow livestock fodder.

      Cattle were first domesticated in Greece or the Balkans about 6000 B.C. They rapidly spread into the Middle East and across Europe. A revolutionary merger of farming and animal husbandry began when cattle reached the growing agricultural civilizations of Mesopotamia. With the development of the plow, cattle both worked and fertilized the fields. Conscription of animal labor increased agricultural productivity and allowed human populations to grow dramatically. Livestock provided labor that freed part of the agricultural population from fieldwork.

      The contemporaneous development of crop production and animal husbandry reinforced each other; both allowed more food to be produced. Sheep and cattle turn parts of plants we can't eat into milk and meat. Domesticated livestock not only added their labor to increase harvests, their manure helped replenish soil nutrients taken up by crops. The additional crops then fed more animals that produced more manure and led in turn to greater harvests that fed more people. Employing ox power, a single farmer could grow far more food than needed to feed a family. Invention of the plow revolutionized human civilization and transformed Earth's surface.

      There were about four million people on Earth when Europe's glaciers melted. During the next five thousand years, the world's population grew by another million. Once agricultural societies developed, humanity began to double every thousand years, reaching perhaps as many as two hundred million by the time of Christ. Two thousand years later, millions of square miles of cultivated land support almost six and a half billion people—5 to 10 percent of all the people who ever lived, over a thousand times more folks than were around at the end of the last glaciation.

      The new lifestyle of cultivating wheat and barley and keeping domesticated sheep spread to central Asia and the valley of the Nile River. The same system spread to Europe. Archaeological records show that between 6300 and 4800 BC adoption of agriculture spread steadily west through Turkey, into Greece, and up the Balkans at an average pace of about half a mile per year. Other than cattle, plants and animals that form the basis for European agriculture came from the Middle East.

      The first farmers relied on rainfall to water their crops on upland fields. They were so successful that by about 5000 BC the human population occupied virtually the entire area of the Middle East suitable for dryland farming. The pressure to produce more food intensified because population growth kept pace with increasing food production. This, in turn, increased pressure to extract more food from the land. Not long after the first communities settled into an agricultural lifestyle, the impact of top-soil erosion and degraded soil fertility—caused by intensive agriculture and goat grazing—began to undermine crop yields. As a direct result, around 6000 BC whole villages in central Jordan were abandoned.

      When upland erosion and the growing population in the Zagros Mountains pushed agricultural communities into lowlands with inadequate rainfall to grow crops, the urgent need to cultivate these increasingly marginal areas led to a major revolution in agricultural methods: irrigation. Once farmers moved into the northern portion of the floodplain between the Tigris and Euphrates rivers and began irrigating their crops, they reaped bigger harvests. Digging and maintaining canals to water their fields, settlements spread