TRANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 75 



play of a cat, ordinarily very clever at catching, as she attempted 

 to seize a peacock-butterfly {Vanessa lo), which settled several 

 times on the ground in front of her. Quietly and slowly she crept 

 within springing distance, but even during the spring the butterfly 

 flew up just before her nose and escaped every time, and the cat gave 

 it up after three attempts. 



In this case the beginning of the action cannot lie in a voluntary 

 action, for the insect cannot know what it means to be caught and 

 killed, and the same is true of innumerable still lower animal forms, 

 the hermit-crabs and the Serpulids, which withdraw with lightning 

 speed into their houses, and so forth. It seems to mo important 

 theoretically, that the same action can be liberated at one time 

 by the will, at another by the inborn instinct-mechanism. In both 

 cases quite similar association-changes in the nerve-centres must 

 lie at the root of the animal's action, but in the first case these 

 are developed only in the course of the individual life by exercise, 

 while in the second they are inborn. In the former, they are confined 

 to the individual, and must be acquired in each generation b}^ imita- 

 tion of older individuals (tradition) and by inference from experience, 

 in the latter they are inherited as a stable character of the species. 



It has been maintained by many that the origin of instincts 

 through processes of selection is not conceivable, because it is 

 improbable that the appropriate variations in the nervous system, 

 which are necessary for the selective establishment of the relevant 

 brain-mechanism, should occur fortuitously. But this is an objection 

 directed against the principle of selection itself, and one which points, 

 I think, to an incompleteness in it, as it was understood by Darwin 

 and Wallace. The same objection can be made to every adaptation 

 of an organ through natural selection : it is always doubtful whether 

 the useful variations will present themselves, as long as they are due 

 solely to chance, as the discoverers of the selective principle assumed. 

 We shall attempt later to fill up this gap in the theory, but, in the 

 meantime, I should like to point out that the process of selection 

 offers the only possible explanation of the origin of instincts, since 

 their origin through modifications of voluntary actions into instinc- 

 tive actions, with subsequent transmission of the instinct-mechanism 

 due to exercise in the individual life, has been shown to be untenable. 



If any one is still unconvinced of this, I can only refer to the 

 cases we have already discussed of instincts which are only exercised 

 once in a lifetime, since, in these, the only factor that can transform 

 a voluntary action into an instinctive one is absent, namely, the 

 frequent repetition of the action. In this case, if any explanation 



