EVOLUTION OF MAN 229 



cranium of the skull to have an average capacity of about 1350 cc. Normal 

 human brains vary greatly in size, however, with the result that cranial 

 capacities vary all the way from 900 to 2300 cc. (Le Gros Clark, 1959). 

 And, significantly, within this rcnge there is no correlation between brain 

 size and degree of intelligence. As extremes among notable men of letters 

 we may cite Anatole France, with a brain volume of 1 100 cc, and Jonathan 

 Swift, with a brain volume of about 2000 cc. 



The large size of brain, particularly of the frontal lobes of the cerebral 

 hemispheres, has resulted in development of a relatively high forehead. 



2. Upright Posture. The upright posture of Homo sapiens entails a 

 whole series of anatomical changes as compared to the structure of pri- 

 mates which do not have this posture. The skull is balanced on the upper 

 end of the vertebral column instead of projecting anteriorly from it. This 

 change, plus, probably, other factors such as expansion of the brain case, 

 has resulted in the shifting forward of the foramen magnum (the opening 

 through which the spinal cord exits from the skull and enters the vertebral 

 column), changing from the posterior position it occupies in forms which 

 walk on all fours. Apes, with their partially upright posture, show an inter- 

 mediate condition in this respect (Fig. 11.5). 



The upright posture in Homo sapiens is made possible by a lumbar 

 curve in the vertebral column — a forward bending of that column in the 

 "small" of the back. Apes lack such a curve (Fig. 11.5). 



One of the greatest changes in the skeletal system connected with upright 

 posture concerns the pelvic girdle. In Homo sapiens the ilium bones are 

 expanded to form a sort of basin supporting the internal organs of the body 

 cavity. In forms which do not walk upright the ilia lack this supportive 

 function and have a much more elongated shape (Fig. 11.5). 



The legs of Homo sapiens are elongated, with relatively straight bones 

 in upper and lower segments, and they terminate in a characteristic foot, 

 most of the lower surface of which is in contact with the ground (planti- 

 grade). 



3. Teeth and Associated Structures. Of the numerous distinguishing 

 characteristics possessed by the teeth of Homo sapiens, we shall list only a 

 few outstanding ones, emphasizing those in which human teeth and jaws 

 contrast with those of apes. 



Homo sapiens differs from apes in the arrangement of the teeth. In apes 

 the incisors are large and the front of the jaw is broad in consequence 

 (Figs. 11.6 and 11.7). The canines are large, projecting tusks; and the 

 premolars and molars extend backward from them in straight rows. The 

 whole effect is that of a straight-sided "U." By contrast the human tooth 



