46 PHYSICAL BASIS OF CIVILIZATION 



demands from a race having suitable bodies adjust- 

 ments to an infinite variety of ever-changing con- 

 ditions, then even the smallest improvement in brain 

 mass or quality is certain to be naturally selected, 

 and brains ever increasing in mass and quality must, 

 caeteris paribus, necessarily emerge in that race. If 

 a race, species or genus, however, is physically well 

 adapted to its environment, and if its organisms are 

 not adapted to an infinite variety of highly complex 

 concerted movements, and if the changes in its 

 environment can ordinarily be met by its natural 

 physical adaptations, then increasing intelligence has 

 comparatively little if any survival value. 



The conditions first mentioned, prevailed among 

 the upright brute ancestry of man, those described 

 in the last sentence among brutes below him. 



The almost unchanging sameness of the relation 

 which has existed during thousands and thousands 

 of years between brutes below man, including apes 

 and elephants, and their environment, indicates the 

 excessively slow rate at which the number and variety 

 of new adjustments of their organisms to environ- 

 ment makes progress, and the enormously long period 

 of time required before even the slightest percepti- 

 ble addition is made to their brain mass or intellec- 

 tual power. 



Differences in brain quality come still more slowly. 

 For while the increase of mass progresses by the 

 smallest quantitative addition, differences in quality 

 can only come into existence after whole tracts or 



