CHAPTER VI 



SENSORY AND RATIONAL DISCRIMINATION 



COMPARATIVE biology places in contrast the sensory 

 discrimination possible to all life, and the rational 

 discrimination characteristic of man. We have now 

 to seek some closer acquaintance with this difference, 

 preparing for an instructed judgment upon the 

 theories concerning the history of life on the earth. 

 The test is reached here. Thus Darwin reasoned 

 concerning the data on which a theory of Evolution 

 must depend : If no organic being excepting man 

 had possessed any mental power, or if his powers had 

 been of a wholly different nature from those of the 

 lower animals, then we should never have been able 

 to convince ourselves that our high faculties had been 

 gradually developed. But it can be shown that there 

 is no fundamental difference of this kind. 1 



Thoroughness of treatment requires that we keep 

 in the first instance to broadly marked differences, so 

 that we may afterwards advance more surely upon 

 resemblances. The question of mental power, or 

 mind here attributed to animals, that is, to some 

 animals, Darwin names the higher mammals, 

 must therefore be held in reserve for separate 

 consideration. We start with a broad distinction, 

 universally recognised. It is the difference between 



1 The Descent of Man, ch. iii. p. 65. 

 122 



