300 Habit and Instinct. 



they be of suitable size and at suitable distance, are 

 indifferently pecked at ; their value as food has to be 

 individually learnt. It may be, however, that the trans- 

 mission of association links is an organic impossibility, 

 and is not to be expected on any theory. 



On the other hand, particular stimuli do unquestion- 

 ably give rise congenitally to particular and hereditary 

 responses. The transmissionist contends that this is due 

 to the repetition of the activity, in response to the given 

 stimulus, and the transmission of the acquired habit. The 

 natural-selectionist regards the congenital connection 

 between stimulus and response as the result of the gradual 

 elimination of those in whom this connection was not 

 adequately established. What is needed in order to dis- 

 tinguish between the rival hypotheses is some really crucial 

 case. If we could in some way exclude natural selection 

 in some instances, and allow it to act in others, we 

 should obtain such crucial cases. And if the habit were 

 equally transmitted, whether natural selection be present 

 or absent, that would present an exceedingly strong point 

 for the transmissionist. 



The nearest approach to such a crucial case which my 

 own observations have afforded me, is that of the reaction 

 of young birds to water. As I have already stated, there 

 does not seem to be any instinctive reaction to the sight of 

 still water, even on the part of ducklings. But so soon as 

 the bill incidentally touches the water, the appropriate 

 drinking response is at once called forth. It may be said 

 that most young birds probably drink first by pecking at 

 dew-drops or rain-drops on the vegetation. Still, ducks, 

 chickens, and other birds have surely had much ex- 

 perience for many generations of drinking from the water 

 of pools and ponds. Now, why does not a chick or 

 duckling respond instinctively to the sight of something 



