136 ZOOLOGY 



Similarly in the history of any species those individuals 

 which respond in suitable or advantageous ways to the stimuli 

 brought to bear on them are selected from generation to gen- 

 eration in preference to those not so responding, and in the 

 course of time certain modes of action become characteristic 

 of the species, even without the necessity of individual ex- 

 perience. In other words the protoplasm has become so modi- 

 fied in a series of generations that responses of a definite kind 

 may be expected of it, which cannot be looked upon as in- 

 dividually acquired habits. These are instincts and embrace 

 many of the most interesting activities which have been men- 

 tioned as characteristic of animals. The instincts of feeding, 

 mating, and the like are examples. If instincts are in conflict, 

 that which is momentarily the stronger prevails. In this possi- 

 bility of situations arising in which the instincts are in conflict, 

 or are unequal to a correct solution, lies the advantage of intelli- 

 gence and choice based upon memory and reason, as adapta- 

 tions whereby experience may contribute to correct responses 

 to external conditions. Of the utmost importance in the devel- 

 opment of intelligence is the introduction of imitation, of train- 

 ing, of experience, of memory, of imagination — factors more or 

 less represented in the activities of all the higher animals. It 

 is necessary to remember that what we call intelligence does 

 not arise suddenly in the animal kingdom and is not confined 

 to the highest animals. Many of the acts usually spoken of as 

 instinctive are not purely so, but are the results, in part of imi- 

 tation, parental or social training, and individual trial and 

 error, and are therefore to be classed as habitual or intelligent. 



167. The Dispersal of Animals and the Formation of 

 Special Faunas. — In section 140 we see that every point occu- 

 pied by the individuals of any species becomes, under natural 

 influences, a centre of distribution from which the species will 

 spread in all directions, unless kept back by adequate barriers. 

 Thus we should expect all animals to be found all over the 

 earth if all the conditions were equally suitable and all animals 

 were equally adaptable to varying conditions. This, however, 

 is not so. Species have unequal powers of adaptation. to the 

 different conditions and thus it comes to be that certain groups 



