186 THE PROBLEMS OF EVOLUTION 



to avoid the unfavorable and to attain favorable 

 surroundings. 



In the higher animals with well developed nerv- 

 ous systems the same result is equally evident. 

 The organism recognizes unfavorable circumstances 

 and turns away from them if possible, or moves 

 toward a favorable condition, or selects the best of 

 an average assortment of alternatives. The activ- 

 ity of the nervous system reaches a higher plane 

 with the elaboration of memory and association. 

 Animals profit by past experience, so that an un- 

 favorable stimulus leaves an impress on the organ- 

 ism which leads to its avoidance in the future. 

 The conditioned reflex appears. An animal may 

 taste unpalatable food and later recognize it by 

 sight or smell and avoid it without tasting again. 

 And the squirrel, without any immediate need for 

 nuts, stores them up for the coming winter. 



What is memory .^^ What is foresight.^ What are 

 the instincts which lead so surely to a given action 

 without any previous experience to guide the in- 

 dividual.^ Without being able to answer these 

 questions simply and directly we find many sig- 

 nificant facts in the manifestation of various de- 

 grees of mental development in the animal 

 world. 



The insects are primarily governed by instincts; 

 indeed, instincts so largely explain their behavior 

 and irregularities are so rare that it is difficult to 



