204 ANIMAL BEHAVIOUR 



there are different grades of instinctive behaviour. There 

 are three main theories at present in the field. (A) Some 

 investigators rank instinctive behaviour as closely comparable 

 to chains of reflex actions, and as due to non-cognitive hered- 

 itary predispositions to follow a certain routine when a 

 number of stimuli present themselves. (B) Others regard 

 instinctive behaviour as quite inseparable from intelligent be- 

 haviour. (C) According to a third view, instinct and in- 

 telligence are two radically different though often co-opera- 

 tive kinds of knowing, which have evolved along divergent 

 lines. 



(A) Some investigators rank instinctive behaviour as near 

 compound reflex actions, as the outcome of non-cognitive 

 hereditary impulsions or predispositions to enter upon a 

 certain routine when a certain trigger is pulled, and to follow 

 on in a perfectly definite manner, the result of one trigger- 

 pulling leading to another trigger, and so on. This may be 

 called the reflex theory of instinctive behaviour, and it is 

 often held by mechanists in the strict sense. It may, how- 

 ever, be held by biologists who admit that vital processes 

 cannot be adequately re-described in terms of chemistry and 

 physics, who are, however, unwilling to admit in instinctive 

 behaviour any reality beyond the physiological processes of 

 the animal's nervous system. We shall call it, therefore, the 

 reflex theory, rather than the mechanistic theory of instinc- 

 tive behaviour. 



Instinctive behaviour agrees with reflex acts in not re- 

 quiring to be learned, in being dependent on hereditary 

 nervous predispositions, and in being exhibited approxi- 

 mately in the same way by all similar individuals of the 

 species. 



It differs from reflex acts in being the activity of the 



