August 16, 1901.] 



SCIENCE. 



2il 



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 com- 

 petition in each generation of the indi- 

 viduals that regenerate best, the process 

 will become more and more perfectly car- 

 ried 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 skep- 

 tical in regard to the possibilities ever be- 

 coming realized. If we examine somewhat 

 more in detail the conditions necessary to 

 bring about this supposed process, we shall 

 find ample grounds for doubt, and even, I 

 think, for denial, that the results could ever 

 have been brought about in this way. 



In the first place the assumption that the 

 regeneration of an organ can be accounted 

 for as a result of the selection of those indi- 

 vidual variations that are somewhat more 

 perfect, rests on the grounds that such vari- 

 ations occur, for the injury itself that acts 

 as a stimulus is not supposed to have any 

 direct influence on the result, i. e., for bet- 

 ter or worse. All that natural selection 

 pretends to do is to build up the complete 

 power of regeneration by selecting the most 

 successful results in the right direction. In 

 the end this really goes back to the assump- 

 tion that the tissue in itself has a fuller 

 power to regenerate completely in some in- 

 dividuals than in others. It is just this 

 difference, if it could be shown to exist, that 

 is the scientific problem. But, even leav- 

 ing this criticism to one side, since it is 

 very generally admitted, it will be clear 

 that in many cases most of the less com- 

 plete stages of regeneration that are as- 

 sumed to occur in the phyletic series could 

 be, in each case, of very little use to the 



individual. It is onlj^ the completed organ 

 that can be used ; hence the very basis of 

 the argument falls to the ground. The 

 building up of the complete regeneration 

 by slowly acquired steps, that can not be 

 decisive in the battle for existence is not a 

 process that can be explained by the theory. 



There is another consideration that is 

 equally important. It is assumed that 

 those individuals, that regenerate better 

 than those that do not, survive, or at 

 least have more descendants ; but it should 

 not be overlooked that the individuals that 

 ai'e not injured (and thej'^ will belong to 

 both of the above classes) are in even a 

 better position than are those that have 

 been injured and have only incompletely 

 regenerated. The uninjured forms, even if 

 they did not crowd out the regenerating 

 ones, which they should do on the hypoth- 

 esis, would still intercross with them, and 

 in so doing bring back to the average the 

 ability of the organism to regenerate. Here 

 we touch upon a fatal objection to the 

 theory of natural selection that Darwin 

 himself came to recognize in the later edi- 

 tions of the ' Origin of Species,' viz., that 

 unless a considerable number of individuals 

 in each generation show the same variation 

 the result will be lost by the swamping ef- 

 fects of intercrossing. If this be granted, 

 there is left very little for selection to do 

 except to weed out a few unsuccessful com- 

 petitors, and if the same causes that gave 

 origin to the new variation on a large scale 

 should continue to act, it will by itself bring 

 about the result, and it seems hardly neces- 

 sary to call in another and questionable 

 hypothesis. 



Finally, a further objection may be stated 

 that in itself is fatal to the theory. We find 

 the process of regeneration taking place not 

 only at a few vulnerable points, but in a 

 vast number of regions, and in each case re- 

 generating only the missing part. The leg 

 of a salamander can regenerate from every 



