238 PHYSICAL BASIS OF CIVILIZATION 



viously, have almost nothing to do with the move- 

 ments of the body. Their habitual occurrence is 

 mostly confined to the lives and labors of scientists, 

 philosophers, statesmen, professional persons, etc. 

 Since these processes are specialized in certain 

 limited areas of the cortex; since the cortex, by 

 weight, is the smaller part of the brain ; therefore is 

 high intellectuality along the line of these processes 

 perfectly compatible with the occurrence in the same 

 persons of comparatively small mass and light weight 

 of the white matter of the brain, which is the larger 

 part of the latter, and therefore determines, far 

 more than the gray cortical tissues, specialized to 

 purely intellectual processes, do, the rank of the 

 brain as a whole by weight. 



The variations observed in the brain weights of 

 civilized persons, and those of persons engaged in 

 purely intellectual occupations, can therefore in no 

 possible way militate against the validity or reliability 

 of the rule derived from observations on the brains of 

 creatures below man, up to and including primitive 

 man, that among them, under normal average 

 conditions, intelligence varies directly with brain 

 weight. 



