232 INTRODUCTION TO EVOLUTION 



projecting chin. In modern Homo sapiens with his shortened tooth row, the 

 lower margin of the jaw extends forward as a chin (see Fig. 11.15). This 

 chin may have evolved as an external buttress against the active stresses to 

 which the broad human jaw is subjected in use (Du Brul and Sicher, 

 1954). 



Modern Homo sapiens lacks heavy ridges of bone projecting over the 

 eyes (supraorbital torus) possessed by apes and earlier hominids. In apes 

 the eyebrow ridges are part of a series of ridges providing attachment 

 (origin) for powerful chewing muscles. In modern Homo sapiens the chew- 

 ing apparatus is reduced and the skull is expanded, providing origin for the 

 chewing muscles without development of the ridges. 



In summary we may characterize the striking features of the skeletal 

 anatomy of modern Homo sapiens as follows: (1) cranial capacity vary- 

 ing from 900 to 2300 cc; (2) high forehead without projecting eyebrow 

 ridges; (3) upright posture, reflected in structure of skull, vertebral col- 

 umn, pelvis, and legs; (4) dental arch a smoothly rounded parabola; (5) 

 canine teeth not projecting beyond the level of the other teeth; (6) no 

 simian gap; (7) first lower premolar not sectorial; (8) lower jaw with a 

 projecting chin; (9) no simian shelf; (10) face orthognathous. 



Having reviewed some of the skeletal features of the end-product of 

 human evolution we now turn our attention to earlier hominids, discuss- 

 ing them in chronological order, starting with the beginning of the 

 Pleistocene period. 



Australopithecines 



The first known fossil of these primates was the skull of a child discov- 

 ered in South Africa in 1924 (for a fascinating account by the discoverer 

 see Dart, 1959). Dr. Dart christened the owner of this skull Australo- 

 pithecus africanus, a name which taken literally signifies that it belongs to 

 a different genus and species from Homo sapiens. (The name written first 

 and capitahzed is that of the genus; the name written second and not 

 capitalized is that of the species, see p. 308.)" Australopithecus" means 

 "southern ape"; this original child and fossils of adults subsequently dis- 

 covered were grouped together into a subfamily, Australopithecinae, of 

 Family Pongidae (apes). Subsequent discoveries and thorough investiga- 

 tion revealed, however, that these South African forms have many char- 

 acteristics of man combined with an ape-sized brain and some other ape- 

 like characteristics. Their resemblance to apes has been emphasized by 

 some writers (e.g., Zuckerman, 1954), their hominid characteristics by 



