Many animals have been greatly changed in form, size and habits by
domestication, especially the dog, sheep, pig, donkey, pigeon and
chicken, so that a great variety of breeds and strains have been
developed. Many kinds of dogs are incapable of existence apart from
human care. The donkey does not run wild, and chickens are never found
at a great distance from human habitations. Others, though much varied
in form and size, are still capable of independent existence, such as
the horse, goat, ox, cat, and goose, but a group like the cheetah, water
buffalo, and swan are only partially domesticated, and little changed by
association with man.