One extra advantage to animals for agriculture was milk. People from the Stone Age figured out cows, goats and sheep gave milk as well as meat. Ancient Arctic Eurasian Natives domesticated reindeer for milk. Sherpas domesticated yaks for milk. Ancient South American Natives domesticated llamas for milk. Huns domesticated horses for milk. Ancient Arabs domesticated camels for milk. Yaks, cows, sheep, reindeer, goats, and even camels are still bred for milk. Only some large mammals which could be easily bred in captivity for agriculture already could give milk