What is Intelligence, and What is Instinct? 31 



The human mind has made great inventions and dis- 

 coveries by arriving through speculation at the knowl- 

 edge of facts which were not known from experience. 

 No one will, on that account, ascribe these discoveries 

 to instinct and not to intelligence. Thus it is like- 

 wise a wrong and one-sided proceeding on the part of 

 modern zoology to assign individual sense experience 

 as the essential criterion of intelligent, in contradis- 

 tinction to instinctive actions. 



Nevertheless, we do not intend to deny that other 

 auxiliary criteria of instinctive actions exist beyond the 

 essential criterion which we have just established. One 

 of these secondary marks is the complete perfection 

 with which many instinctive actions are performed, 

 without previous practice or experience on the part of 

 the animal, so that they need not be learnt, but depend 

 almost entirely on inherited dispositions. Another auxil- 

 iary character of instinctive actions is the constant uni- 

 formity with which they are performed by almost every 

 individual of the same species. Yet, these two auxiliary 

 marks are by no means essential criteria. For there 

 are a few hereditary instincts that require previous 

 practice and hence individual experience for their per- 

 fect development. Thus the so-called "raptorial" in- 

 stincts of cats must be gradually developed through 

 the instinctive "playfulness" of the kitten, which does 

 not so far perceive the purpose of an amusement that 

 is meanwhile only pleasant to it. 1 Moreover, the exer- 

 cise of hereditary instincts in members of the same 

 species is modified by the variety of individual dispo- 



) See Gross, "The Play of Animals" (German, 2d edition. Yena, 

 1896). 



