Wheat and wild pigs existed in the Fertile Crescent, but not in the Americas; wheat and wild pigs existed in the Andes area, but not in Africa or Asia. Furthermore, just a few hundred of the world's 200,000 plant species have been domesticated, and only five of them — wheat, corn, rice, barley, and sorghum — have provided more than half of the calories needed to maintain human life in recent decades.
Some suggest that a cold and dry period between 11,000 and 9500 B.C.E., a very fast but brief pause in the main trend of global warming, was the catalyst for the shift to agriculture.
According to archeological evidence, the shift to an agricultural way of life in portions of this region occurred quite fast, maybe within 500 years. Large expansions in the size of towns, which now housed several thousand people, were signs of that transition.
In the Americas, a new pattern of agricultural growth emerged. Plant domestication in the Americas happened in a variety of areas, similar to the Agricultural Revolution in Africa, including the coastal Andean regions of western South America.