134 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, 

 the stronger prevails. In this possibility of situations arising 

 in which the instincts are in conflict, or are unequal to a correct 

 solution, lies the advantage of intelligence and choice, as adap- 

 tations whereby correct responses may be made to external 

 conditions. Of the utmost importance in the development of 

 intelligence is the introduction of imitation, of training, of 

 experience, of memory, factors more or less represented in 

 the activities of all the higher animals. It is necessary to re- 

 member 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 imitation, parental 

 or social training, and individual trial and error, and are there- 

 fore to be classed as 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 



