Domestic cattle now outweigh every wild mammal on Earth combined
Taming an animal and domesticating it are different things. A hand-raised cheetah can be tame yet wild, while a Spanish fighting bull is domestic but far from docile. Domestication rewrites a lineage's genes over generations, and it has worked so well that cattle alone now outweigh all wild mammals together.
Dogs came first, descended from wolves at least 15,000 years ago in northern Eurasia, before farming existed. They crossed into the Americas with people before the Bering land bridge closed and may have reached Australia as the ancestors of dingoes. Unusually, early dogs were chosen for behaviour rather than meat or milk.
Livestock followed after the ice age. Warming after the Last Glacial Maximum, a harsh cold snap called the Younger Dryas 12,900 years ago, and then milder Holocene conditions pushed foragers to supplement hunting. Goats, pigs, sheep and cattle were domesticated in the Fertile Crescent 10,000 to 11,000 years ago, a separate pig lineage in East Asia about 8,000 years ago, horses on the Central Asian steppe 5,500 years ago and chickens in Southeast Asia 4,000 years ago. The Andes independently produced llamas, alpacas and guinea pigs, and Mesoamerica gave the world turkeys.
Researchers describe three routes in. Some animals, such as dogs and cats, drifted into human settlements on their own; others were sought for food, like sheep and yak; a third group, including horses and camels, was recruited for hauling and riding. Good candidates share traits such as social living, flexible diets, quick bonding between parents and young, and calm reactions to people and new surroundings. Breeding in captivity is not enough: tigers and gorillas reproduce readily in zoos without being domestic, and Asian elephants, though trained, still breed outside human control.
Charles Darwin was first to separate deliberate breeding from unconscious selection. Many domestic animals share a cluster of changes, including floppy ears, altered coat colours, smaller teeth and brains, and youthful behaviour that lasts into adulthood.
Source: Domestication of vertebrates
