The ExpUuialioii of Adaptations. hOl 



may be of interest to show that the prevailing view, ac- 

 cording to which A\'allace's form of the theory of selec- 

 tion is the only one which will account for adaptations, 

 is erroneous. 



The \iew that all the characters of organisms varv 

 in everv desired direction, and tliat tlie sliHitest deviation 

 may be subjected to the struggle for existence, and can 

 be accentuated to, and finally fixed at, the necessary de- 

 gree of development, is certainly an extremelv convenient 

 one. I willinHv adnn"t that almost anvthin^- can he 

 squared with this theory in a very plausible wav, and 

 that explanations of this kind are very attractive to the 

 student ; but this is not science. The contradictions in 

 such a system must be satisfactorily explained before it 

 is accepted ; and if we attempt to do this, we soon come to 

 the conclusion that the hypothesis itself is not in harmonv 

 with the available evidence. 



The limits of the a])])licability of the theory of selec- 

 tion, as applierl to this question, are known to evervbody ; 

 and without doubt they are extremely wide. How mucli 

 the theory of mutation has to offer in this respect we 

 do not know, because no attempt to estimate this has as 

 yet been made, but everything points to the conclusion 

 that this theory will explain adaptations just as com- 

 pletely, or rather just as incompletely, as the present 

 view. It will, however, always have the special feature 

 of emphasizing the hypothetical ])arts (^f the argument, 

 rather tlian of dismissing" them into the backciround. 



At the present time the theory of selection has still 

 the larger number of adherents ; but amongst the ycMinger 

 investigators a train of th(^ught is dex'eloping whicli. as 

 we have seen above, ascribes a greater importance to 

 discontinuous changes. For them fluctuating variability 



