The mammalian family that originally included humans and immediately ancestral forms now extinct. Hominids were distinguished from the apes (Pongidae) (a) by the possession of a much larger brain, in which the frontal and occipital lobes are especially well developed, allowing more complex behaviour including communication by speech; (b) by a fully erect posture facilitated by the positioning of the foramen magnum beneath the skull so that the head is held upright; (c) by a bipedal gait; and (d) by the slow rate of post-natal growth and development, which favours complex social organization and the emergence of distinct cultures. However, the Pongidae is no longer considered to be a monophyletic group and most modern authorities include the chimpanzee (Pan troglodytes), bonobo (P. paniscus), gorilla (Gorilla gorilla), and probably the orang-utans (Pongo pygmaeus and P. abellii) in the Hominidae, on the ground that they are close to humans phylogenetically (see phylogeny). The Hominidae also includes the genera Paranthropus and Australopithecus (but see australopithecines) as well as Homo. Ramapithecus, once considered a possible human ancestor, is now known to be more closely related to the orang-utans.