Humans belong to the class known as Mammalia of the Animalia, or animal, kingdom. Members of the Mammalian class are often called mammals. They have spines and hair - except for whales older than fetuses - and in natural circumstances, they feed their offspring milk from maternal mammary glands.
Unlike other classes of vertebrates, the red blood cells of mammals do not have a nucleus, and their lower jaw bones are attached directly to the skull instead of to a connecting bone. The babies of mammals develop in a mother's womb until birth, with the exception of the duck-billed platypus and a few other egg-layers.