SENSES, INSTINCTS, AND INTELLIGENCE 337 



not require to be " learned," that it is definite and related 

 to particular circumstances, that it is shared equally by 

 all members of the species of the same sex, that it exhibits 

 considerable tyranny of routine. Among birds there is 

 much instinctive behaviour in courtship, nest-building, 

 and brooding, in dealing with food, and in achievements 

 of locomotion. 



On the initiative side, but higher than instinctive 

 behaviour, we must now rank intelligent behaviour, which 

 demands inferential learning. There is some degree of 

 perceptual inference, some " picture-logic " at least, some 

 ** putting two and two together." 



The frequent repetition of an intelligent action in the 

 lifetime of the individual leads to individual habituation — 

 but there is no conclusive evidence that this can be entailed 

 so as to enrich the hereditary racial equipment. 



It is highly characteristic of birds that intelligence and 

 intelHgent habits may mingle with instinctive behaviour 

 in subtle ways ; as we see in the individualities of nests 

 in difficult situations or in the utilisation of difficult food- 

 material. 



The inclined plane ends on its initiative side in rational 

 conduct, which implies conceptual inference or experi- 

 menting with abstract ideas. So far as we know, this kind 

 of activity is restricted to man and is only occasionally 

 exhibited. 



On the enregistration side, it may be suggested that the 

 highest grade is that of unconscious cerebration, where a 

 result is reached, not by controlled experimenting, nor by 

 attending the mind thereunto, but more intuitively or 

 instinctively — as the spontaneous outcome of racial and 

 individual engraining. The " inspiration " may take the 

 form of a sudden action in a crisis, of solving an arith- 

 metical or a mathematical problem without knowing how, 

 or of a work of art. Perhaps the nightingale's song may be 

 an illustration. 



