DIMINUTION OF THE JA WS. 1 1 



The striking variability of the human jaw is 

 strongly opposed to the idea of its being under 

 the direct and dominant control of so uniform a 

 cause as ancestral use and disuse. Mr. Spencer 

 regards a variation of I oz. as a large one, but I 

 found that the English jaws in the College of 

 Surgeons varied from rg oz. to 4*3 oz. (or 5 oz. 

 if lost teeth were allowed for) ; Australian jaws 

 varied from 2 oz. to 4*5 oz. (with no lost teeth to 

 allow for) ; while in Negro jaws the maximum 

 rose to over $J oz. 1 I In spite of disuse some 

 European jaws were twice as heavy as the light- 

 est Australian jaw, either absolutely or (in some 

 cases) relatively to the cranium. ] The uniformity 

 of change relied upon by Mr. Spencer is scarcely 

 borne out by the facts so far as male jaws are 

 concerned. The great reduction in the weight 

 of female jaws and skulls evidently points to 



1 Inclusive in each case of fixed strengthening wire weighing 

 about a sixteenth of an ounce or less. 



