486 THE GENERAL PRINCIPLES OF ZOOLOGY 



majority who hold to it believe that though we can explain by it 

 many phenomena of instinctive behavior, yet our knowledge of 

 the subject is so very imperfect that it certainly leaves much 

 unexplained ; there may very well be, then, some other principle 

 which acts in conjunction with natural selection. 



The various forms of animal behavior which we have noted 

 thus far have several points in common ; they are all inherited ; 

 all are performed without previous experience and in the same 

 way by similar individuals ; they have not been learned ; they 

 are involuntary. But for most animals such simple methods of 

 organic response are insufficient to meet the varying conditions 

 of their environment. Instinctive acts, the highest form of 

 inherited automatic activity, are early modified by experience. 

 The experiment was made of placing before a very young chick 

 some finely cut bits of bright yellow orange rind; the chick 

 pecked at them as it did instinctively at any attractive object, 

 but found them distasteful and let them alone. Then a part of 

 a finely chopped, hard-boiled egg was placed before the chick; 

 it ate the white of the egg but left the yolk untouched, its yel- 

 low color recalling the experience of the orange rind, and the 

 young bird could not distinguish between them by sight or 

 smell. Thus it had learned to profit by experience and so 

 manifested the presence of an effective consciousness in a 

 distinctly volitional act, — a manifestation of intelligence. Here 

 the association of the disagreeable taste with the yellow color 

 was sufficiently vivid to prevent the chick from pecking at a 

 similar object. 



The intimate association of intelligence with instinctive acts 

 may be brought about by the necessity for a choice between 

 several instincts which may be presented to the animal's con- 

 sciousness at one and the same time. The cat sunning herself 

 at the bottom of the house steps is suddenly confronted by a 

 small terrier. She may follow her instinct to run and seek 

 shelter in the house ; she may stand her ground and follow 

 her instinct to scratch ; or she may climb the neighboring fence 

 or tree. Thus several instincts, any one of which may be effec- 

 tive, present themselves at the sight of the young dog, and the 

 necessity for choosing between them makes her action, which 

 would otherwise be purely instinctive, an intelligent one ; but 





