Agriculture involves the active production of plants and animals in human-created ecosystems. It includes cultivating soil, growing and harvesting crops, and raising livestock. Agriculture developed independently in many places around the world starting around 14,500-12,000 years ago. Early domesticated crops include barley in the Middle East, millet in China, and squash in the Americas. Domesticated livestock developed during this same period, although dogs were domesticated earlier. Agriculture can be viewed as a farming system involving inputs like seeds, fertilizers, machinery and labor and outputs like crops, wool, dairy and poultry products.