INSTINCT AND REASON 251 



In these regards, the nest-building and home-making 

 animals have the advantage over those that have not these 

 instincts. The animals that mate for life have the advan- 

 tage over polygamous animals, and those whose social or 

 mating habits give rise to a division of labor over those 

 with instincts less highly specialized. 



The interesting instincts and habits connected with nest 

 or home building and the care of the young are discussed 

 in the next chapter. 



139. Variability of instincts. When we study instincts 

 of animals with care and in detail, we find that their regu- 

 larity is much less than has been supposed. There is as 

 much variation in regard to instinct among individuals as 

 there is with regard to other characters of the species.' 

 Some power of choice is found in almost every operation of 

 instinct. Even the most machine-like instinct shows some 

 degree of adaptability to new conditions. On the other 

 hand, in no animal does reason show entire freedom from 

 automatism or reflex action. " The fundamental identity 

 of instinct with intelligence," says an able investigator, " is 

 shown in their dependence upon the same structural mech- 

 anism (the brain and nerves) and in their responsive adap- 

 tability." 



140. Reason. Reason or intellect, as distinguished from 

 instinct, is the choice, more or less conscious, among re- 

 sponses to external impressions. Its basis, like that of in- 

 stinct, is in reflex action. Its operations, often repeated, 

 become similarly reflex by repetition, and are known as 

 habit. A habit is a voluntary action repeated until it be- 

 comes reflex. It is essentially like instinct in all its mani- 

 festations. The only evident difference is in its origin. 

 Instinct is inherited. Habit is the reaction produced with- 

 in the individual by its own repeated actions. In the 

 varied relations of life the pure reflex action becomes inade- 

 quate. The sensorium is offered a choice of responses. To 

 choose one and to reject the others is the function of intel- 



