578 Professor 0. Lloijd Morgan [Jan. 28, 



And Eomanes, to whose ever-kindly sympathy I am deeply indebted, 

 adhered to this view in spite of modern criticism. There is not much 

 in my own observational work which has any decisive bearing on the 

 question. But there are one or two points which are perhaps worthy 

 of consideration. The part played by acquisition in the field of 

 behaviour is the establishment of definite relations between particular 

 groups of stimuli and adaptive responses. If this be so, and if 

 acquired modifications of brain-structure be transmitted, we might 

 reasonably expect that the sight of a dog would have a similar effect 

 on young pheasants to that which it has on their parents. But this 

 does not appear to be the case. Again, one might reasonably expect 

 that the sight of water would evoke a drinking response in recently 

 hatched birds, just as the sight or scent of a Yucca flower excites a 

 definite response in the Yucca moth. But here, too, this is not so. 

 Thirsty chicks and ducklings seem to be uninfluenced by the sight 

 of water in a shallow tin. They may even run through the liquid 

 and remain unaffected by its presence. But if they chance to peck at 

 a grain at the bottom of the tin or a bubble on the water, as soon as 

 the beak touches the liquid, this stimulus at once evokes a drinking 

 response again and again repeated. Why does the touch of water in 

 the beak excite a congenital response, while the sight of water fails 

 to do so? I believe it is because under natural conditions the chicks 

 peck at tbe water in imitation of the mother, who thus shields them 

 from the incidence of natural selection. Under these circumstances 

 there is no opportunity for the elimination of those who fail to 

 respond at the mere sight of water, and consequently no selective 

 survival of those who do thus respond. Bat though the hen can 

 lead her young to peck at the water, she cannot teach them the 

 essential movements of beak, mouth and gullet which are necessary 

 for the completed act of drinking. In this matter she cannot shield 

 them from the incidence of natural selection. Those which, on 

 pecking the water, failed to respond to the stimulus by drinking, 

 would assuredly die of thirst and be eliminated ; the rest would 

 survive and transmit the congenital instinctive tendency. Thus it 

 would seem that when natural selection is excluded, a special mode 

 of behaviour has not become congenitally linked with a visual 

 stimulus ; but where natural selection is in operation, this behaviour 

 has become so linked with a touch or taste stimulus in the beak. 

 Similarly in the case of the pheasants and the dog. The parent birds 

 warn the young of his approach, and thus prevent the incidence of 

 natural selection. Hence there is no instinctive response to the sight 

 of a terrier. 



No doubt there are many cases of complex behaviour, seemingly 

 instinctive, which are difficult to explain by natural selection alone, 

 and which have the appearance of being due to the inheritance of 

 acquired habits. I have, however, elsewhere suggested that acquired 

 modifications may, under the conditions of natural selection, foster 

 the development of " coincident " variations of like nature and direc- 



