INSTINCT. 67 



would expect from the inheritance of habits acquired in refer- 

 ence to definite objects. If the instinct to follow in chicks 

 came from the habit of following (acquired, of course, with a 

 hen as the object followed), we would expect it to require as 

 its object something at least like a hen. As a matter of fact 

 it does not. 



Professor Whitman's fourth contention, that, since instinc- 

 tive activities are the results of gradual development, they 

 should be, not merely enumerated, described, and explained as 

 to their utility, but also explained as to their development and 

 relationships, comes as a timely piece of advice. Even if 

 students of instinct should never succeed in working out the 

 genealogy of one instinct out of a hundred, the genetic method 

 of study would be valuable by preventing mythologizing and 

 reminding the student that instinctive activities are expressions 

 of organic structure as truly as are the activities of digestion 

 or excretion. And, in closing this lecture, I wish to give some 

 samples of development among instincts. Professor Whitman 

 has traced the ancestry of some particular acts. Let us look 

 at some instinctive activities which persist, with modifications 

 of course, over a wide range of forms, which correspond in a 

 way to the notochord, or brain-eye, or arthropod appendages 

 among physical organs. The frog, lizard, chick, and cat all 

 react to irritation of the head by scratching with the hind leg 

 with a quick, repetitive motion that is startlingly alike in the 

 last three. Here we have an instinct which apparently ranges 

 nearly over a subkingdom. In the primates it is modified, the 

 monkeys (at least some of them) using either hind or front 

 limb for the purpose, while man uses only the front. Distaste 

 at confinement is another widely prevalent instinct, which may 

 be a foundation-stone laid by germinal variation once for all. 

 The instinct to follow is another. It might be that the grega- 

 rious instincts originated as exaggerations of it by the selection 

 of individuals in whom the impulse to follow varied in the line 

 of greater intensity. 



