The active production of useful plants or animals in ecosystems that have been created by people. Agriculture may include cultivating the soil, growing and harvesting crops, and raising livestock. Agriculture was independently developed in many places, including the Middle East, East Asia, South Asia, and the Americas. The earliest evidence for agriculture has been found in the Middle East and dates to between 14,500 and 12,000 BP. Early cultivars include wild barley (Middle East), millet (China), and squash (the Americas). The domestication of many animals now considered to be livestock occurred during roughly the same period, although dogs were domesticated considerably earlier. Slash-and-burn land-clearing methods and crop rotation were early agricultural techniques. Steady improvements in tools and methods over the centuries increased agricultural output, as did mechanization, selective breeding and hybridization, and, beginning in the 20th century, the use of herbicides and insecticides.