1 08 RE GENERA TION 



So firm a hold has the Darwinian doctrine of utility over the 

 thoughts of those who have been trained in this school, that whenever 

 it can be shown that a structure or a function is useful to an animal, 

 it is without further question set down as the result of the death 

 struggle for existence. A number of writers, being satisfied that the 

 process of regeneration is useful to the animal, have forthwith sup- 

 posed that, therefore, it must have been acquired by natural selection. 

 Weismann has been cited as an example, but he is by no means alone 

 in maintaining this attitude. It would be entirely out of place to 

 enter here into a discussion of the Darwinian theory, but it may be 

 well worth while to consider it in connection with the problem of 

 regeneration. 



We might consider the problem in each species that we find 

 capable of regenerating ; or, if we find this too narrow a field for our 

 imagination, we might consider the process of regeneration to have 

 been "acquired by selection in the lower and simpler forms," and 

 trace its subsequent progress as it decreased in the course of phylog- 

 eny " in correspondence with the increase in complexity of organiza- 

 tion," or with the decrease of exposure to injury. At the risk of 

 adopting the narrower point of view I shall confine the discussion to 

 the possibility of regeneration being acquired, or even augmented, 

 through a process of natural selection in any particular species. 



The opportunity to regenerate can only occur if a part is removed 

 by accident or otherwise. On the Darwinian theory we must suppose 

 that of all the individuals of each generation that are injured, /';/ 

 exactly the same part of the body, only those have survived or have 

 left more offspring that have regenerated. In order that selection may 

 take place, it must be supposed that amongst these individuals injured 

 in exactly the same region, regeneration has been better in some forms 

 than in others, and that this difference is, or may be, decisive in the 

 competition of the forms with each other. The theory does not 

 inquire into the origin of this difference between individuals, but 

 rests on the assumption of individual differences in the power to 

 regenerate, and assumes that these differences can be heaped up by 

 the survival and inbreeding of the successful individuals; i.e. it is 

 assumed that, by this picking out or selection through competition in 

 each generation of the individuals that regenerate best, the process 

 will become more and more perfectly carried out in the descendants, 

 until at last each part has acquired the power of complete regeneration. 



There are so many assumptions in this argument, and so many 

 possibilities that must be realized in order that the result shall follow, 

 that, even if the assumptions were correct, one might still remain 

 sceptical in regard to the possibilities ever becoming realized. If we 

 examine somewhat more in detail the conditions necessary to bring 



