66 PHYSICAL BASIS OF CIVILIZATION 



The argument may, therefore, be resumed with 

 increased confidence where it was interrupted. 



Since the brutes below man are adjusted to the 

 conditions of existence by their natural physical 

 attributes, conduct plays but a small and unimpor- 

 tant part in their survival. But it was very different 

 with the upright brute ancestors of man. For since 

 they were physically unadapted to the struggle for 

 existence and afflicted with many special infirmities, 

 conduct was the only means by which they possibly 

 could escape extermination. No other faculty is 

 of such universal, infinite applicability in adjusting 

 the conduct of a creature to its environment as in- 

 telligence. To creatures having organisms adapted 

 to an infinitely great variety of compound concerted 

 motions, intelligence must therefore be of great im- 

 portance. Therefore, to show the overwhelming 

 survival value of intelligence in the case of the primi- 

 tive brute ancestry of the human race, it only 

 remains necessary to ascertain whether or not, dur- 

 ing the long interval referred to above, there existed 

 anything in their organisms which acted as a natural 

 and continuous incentive for the exercise and use 

 of their intelligence. 



the ground is approached, therefore the real ratio of increase 

 is much greater than the ratio above stated, and probably at least 

 equal to the cube of the altitude. 



No observer of four-footed animals can have failed to notice 

 that the mentally energetic and intellectually superior among 

 them make frequent efforts to elevate their heads for the purpose 

 of hearing and seeing, more especially when their curiosity or 

 apprehension is aroused, having learned, by experience no 

 doubt, the advantage of this mode of conduct. 



