For over 40 years South Africa and for over 25 years East Africa have been yielding fossilized remains of creatures identified on their bony structure as lowly members of the Hominidae or human family. From five sites in the Republic of South Africa (Taung, Sterkfontein, Kromdraai, Makapansgat and Swartkrans) and from three sites in the Republic of Tanzania (Garusi, Olduvai and Peninj) have emerged a considerable number of hominid fossils of the Lower and Middle Pleistocene. Most of them have been classified as members of an extinct hominid genus called by R. A. Dart, the discoverer of the first specimen, Australopithecus. Although variable among themselves, the structural features which aligu these fossils with the Hominidae, rather than with the family of the apes or Pongidae, are as follows:—
(1) Australopithecus showed modifications of his skeleton—especially the pelvis, femur, ankle and foot—which permit us to infer that he walked upright, even though such modifications had not progressed as far as in hominids of the genus Homo.
(2) The calvaria or brain-case of Australopithecus was characterized by a number of hominid features, such as marked flexion of the axis of the cranial base; forward displacement of the occipital condyles by which the skull articulates with the vertebral column; a small, low nuchal area at the back of the base of the cranium, for the attachment of those muscles which tether the back of the cranium to the trunk—the last two features suggesting a different, more man-like poise of the cranium on the spine; the consistent development, early in life, of a pyramidal mastoid process as in man, and unlike the apes in which this process develops inconsistently and then only later in life (Schultz 1950).
(3) The canine teeth of Australopithecus, like those of Homo, lacked the enlargement and marked interlocking which characterizes the upper and lower teeth of the apes—correspondingly, Australopithecus lacked the diastemata or gaps which, in apes, lodge the projecting tips of the enlarged canines.
(4) Another dental characteristic shared by Australopithecus with Homo was the bicuspid structure of the first lower premolar tooth: in apes, this tooth does not possess two sub-equal cusps but is a cutting or sectorial tooth with one predominating cusp, like a canine tooth.
(5) Although the brain-size of Australopithecus (as inferred from the volumetric capacity of the brain-case) was no bigger than that of some largerbrained apes, the shape or morphology of the brain, as preserved in endocranial casts, approached more closely to that of early Homo than to that of the apes. We have, however, no direct evidence whether these external observable differences between the brains of Australopithecus and of apes were paralleled by internal, microscopic, structural differences such as those which have been demonstrated between modern man and modern apes.
(6) Many other detailed morphological features of the skull, the teeth and other bones of Australopithecus showed human resemblances.