An agrarian society, or agricultural society, is any community whose economy is based on producing and maintaining crops and farmland. Another way to define an agrarian society is by seeing how much of a nation's total production is in agriculture. In an agrarian society, cultivating the land is the primary source of wealth. Such a society may acknowledge other means of livelihood and work habits but stresses the importance of agriculture and farming. Agrarian societies have existed in various parts of the world as far back as 10,000 years ago and continue to exist today. They have been the most common form of socio-economic organization for most of recorded human history. Agrarian society were preceded by hunters and gatherers and horticultural societies and transition into industrial society. The transition to agriculture, called the Neolithic Revolution, has taken place independently multiple times. Horticulture and agriculture as types of subsistence developed among humans somewhere between 10,000 and 8,000 years ago in the Fertile Crescent region of the Middle East. The reasons for the development of agriculture are debated but may have included climate change, and the accumulation of food surplus for competitive gift-giving. Most certainly there was a gradual transition from hunter-gatherer to agricultural economies after a lengthy period when some crops were deliberately planted and other foods were gathered from the wild. An example of this transition can be found in the cultivation of wild cereals by hunter-gatherers in the Central Sahara. Between 7500 BCE and 3500 BCE, undomesticated central Saharan flora were farmed, stored, and cooked, and domesticated animals (e.g., Barbary sheep) were milked and managed, by hunter-gatherers near the Takarkori rockshelter, which is representative of the broader Sahara; this continued until the beginning of the Pastoral Neolithic in the Sahara. In addition to the emergence of farming in the Fertile Crescent, agriculture appeared: by at least 6,800 BCE in East Asia (rice) and, later, in Central and South America (maize and squash).