Wild camels sometimes breed with domesticated or feral camels. It occurs in humans and certain breeds of domesticated animals. Feral cattle are defined as being 'cattle that are not domesticated or cultivated'. However, an animal merely bred in captivity is not necessarily domesticated. Several bovid species have been domesticated by human beings. Goats were first domesticated as livestock more than 10,000 years ago. Unlike most horses and donkeys, onagers have never been domesticated. Unlike their closest relatives, horses and donkeys, zebras have never been truly domesticated. Einkorn wheat was one of the first plants to be domesticated and cultivated. It was among the first plants to be domesticated and cultivated. Cattle have been domesticated since approximately 10,500 years ago. Pigs were domesticated in Mesopotamia around 13,000 BC. It is believed that pigs were first domesticated there. Pigs were initially domesticated in North Africa and Eurasia. Sheep were domesticated in Mesopotamia between 13,000 and 11,000 years ago.