A hominid is a primate in the family of Hominidae of which Homo sapiens are the only surviving member. Hominids are bipedal (walk on two legs), have an enlarged brain capacity, a flattened face, and reduction of size of the jaw. According to evolutionary theory, the australopithecines, homos (homo habilis, homo erectus), and homo sapiens are all hominids. Hominids are supposed to be common ancestors of humans but not apes.