Because of its rich resources of wild foods, the Fertile Crescent supported a relatively dense population of semi-nomadic hunter-gatherers during the last Ice Age. As the Ice Age came to an end approximately 10,000 years ago, the climate of the Near East became drier, reducing the availability of wild foods. The hunter-gatherers living in the region responded to these changes by deliberately planting the seeds of their favorite food plants close to their campsites to improve the security of their food supply. they also began to control and manage herds of wild cattle, sheep and goats, achieving this by penning them up and selectively slaughtering young male animals while releasing females of breeding age. In herd animals, only dominant males get to mate, so large numbers of young males can be taken without depleting the breeding stock. From these simple beginnings there followed a long process of selective breeding to produce fully domesticated crops and farm animals best suited to supplying grain, meat, milk and skins for clothing and shelter. The need for vessels to store and prepare food spurred the development of pottery technology.
In the Fertile Crescent, the transition from hunting and gathering to complete reliance on agriculture and settlement in permanent villages took around 2,000 years and, once complete, there could be no going back. With hunter-gatherers, population is limited by the natural productivity of the environment. If the population rises to an unsustainable level, starvation soon restores the natural balance. Hunter-gatherers who survived into the modern age often took extreme measures to limit population growth, for example, by killing or abandoning unwanted babies. Farming broke this link, though perhaps not permanently. Even simple subsistence farming can support a much denser population than hunting and gathering. The human population began to rise, and, as it did so, it inevitably became more reliant on farming for its food supply. However, more mouths also meant more hands, enabling more land to be brought into cultivation and worked more intensively, so increasing the food supply even more. More people also meant more brainpower and the pace of cultural and technological change began to increase too.
Except for brief pauses resulting from plagues and famines, the global population has risen inexorably ever since the introduction of agriculture, aided by ever more efficient farming methods and technology.
As the population in the Fertile Crescent grew, settlers moved out of established villages to create new villages on virgin land. As the ever-growing numbers of farmers encroached on thier hunting grounds, the remaining hunter-gatherers in the region were forced to take up farming too in order to survive. By around 6000 B.C.E., the farming way of life had become widespread in the Near East, but only in areas with sufficient rainfall for dry farming. Around 5900 B.C.E. , farmers in the foothills of the Zagros mountains began to dig canals to carry water from rivers to their fields to irrigate them during the dry season. This was the key development that allowed farmers to settle in Sumer and unlock the tremendous fertility of its alluvial soils.
The Ancient World, John Haywood, Quercus Books, Massachusetts, 2010