THE ORIGIN OF INSTINCT 117 



higher vertebrates, such as the act of sucking performed 

 so perfectly without any education or practice by the 

 newly-born mammal. But in the lower animals true 

 instincts are relatively far more numerous and play 

 a most prominent part in the life of the individual. In 

 these cases of true instinct I would suggest that we are 

 dealing with actions which have never been intelligent at 

 any time in the past history of the species, but have 

 arisen through the operation of Natural Selection upon 

 the nervous system. Certain activities which are most 

 strongly held to be the outcome of the transmission of 

 experience and the acquired results of practice obviously 

 cannot be explained in this way. 



For instance, how upon any such hypothesis can you 

 explain the wonderful structure of the cocoon spun by the 

 larva of an insect ? The view would be, I suppose, that 

 the ancestral larva spun a cocoon which was not much of 

 a success and was in consequence attacked by enemies ; 

 that the larva observed these attacks, and accordingly 

 improved its cocoon. But that is not the way in which 

 the struggle for existence is waged with insects. If the 

 larva failed, it failed, and that would be the end of the 

 matter. It has no chance of improvement ; it has no 

 opportunity of learning by experience. Its only chance 

 of survival is to avoid experience of foes altogether ; 

 experience is the most dangerous thing in the world to 

 an edible insect. This becomes still more obvious when 

 we remember that failure or success is almost always 

 determined long after the cocoon is made. The cater- 

 pillar perhaps spins the cocoon in autumn, but the real 

 stress of competition will come in winter, when insect- 

 eating animals are pressed hard with hunger and search 

 high and low for food. But the caterpillar by this time 

 is a chrysalis and of course has no opportunity of im- 

 proving the cocoon. The selective test is applied long 

 after the operation has been performed, and when there 

 is no possibility of gaining by experience. We are thrown 

 back, then, solely upon Natural Selection, which acts on 

 the nervous system of the caterpillar, and thus compels 

 it to make the cocoon in a certain way. In other words, 



