432 Mental Factors in Evolution 



treatment than Darwin's conception of an impelling force, and that 

 it is in line with the main trend of Darwin's thought. 



In a characteristic work, characteristic in wealth of detail, in 

 closeness and fidelity of observation, in breadth of outlook, in 

 candour and modesty, Darwin dealt with The Expression of the 

 Emotions in Man and Animals. Sir Charles Bell in his Anatomy 

 of Expression had contended that many of man's facial muscles had 

 been specially created for the sole purpose of being instrumental in 

 the expression of his emotions. Darwin claimed that a natural 

 explanation, consistent with the doctrine of evolution, could in many 

 cases be given and would in other cases be afforded by an extension 

 of the principles he advocated. "No doubt," he said 1 , "as long as 

 man and all other animals are viewed as independent creations, an 

 effectual stop is put to our natural desire to investigate as far as 

 possible the causes of Expression. By this doctrine, anything and 

 everything can be equally well explained.... With mankind, some 

 expressions... can hardly be understood, except on the belief that man 

 once existed in a much lower and animal-like condition. The com- 

 munity of certain expressions in distinct though allied species... is 

 rendered somewhat more intelligible, if we believe in their descent 

 from a common progenitor. He who admits on general grounds that 

 the structure and habits of all animals have been gradually evolved, 

 will look at the whole subject of Expression in a new and interesting 

 light." 



Darwin relied on three principles of explanation. " The first of 

 these principles is, that movements which are serviceable in gratifying 

 some desire, or in relieving some sensation, if often repeated, become 

 so habitual that they are performed, whether or not of any service, 

 whenever the same desire or sensation is felt, even in a very weak 

 degree 2 ." The modes of expression which fall under this head have 

 become instinctive through the hereditary transmission of acquired 

 habit. "As far as we can judge, only a few expressive movements 

 are learnt by each individual ; that is, were consciously and voluntarily 

 performed during the early years of life for some definite object, or 

 in imitation of others, and then became habitual. The far greater 

 number of the movements of expression, and all the more important 

 ones, are innate or inherited ; and such cannot be said to depend on 

 the will of the individual. Nevertheless, all those included under 

 our first principle were at first voluntarily performed for a definite 

 object, namely, to escape some danger, to relieve some distress, or 

 to gratify some desire 3 ." 



" Our second principle is that of antithesis. The habit of volun- 



1 Expression of the Emotions, p. 13. The passage is here somewhat condensed. 

 - Ibid. p. 368. 3 Ibid. pp. 373, 374. 



