THE STRUGGLE FOR EXISTENCE. 65 



Darwinian theory still stands unassailable as the one 

 and only rational scientific explanation of evolution by 

 "natural" forces, whose action can be observed, tested, 

 and measured. Nevertheless, the critics are quite right 

 in demanding convincing evidence for every step in the 

 argument. 



The modern developments of the study of heredity and 

 variation on mendelian lines, far from weakening the 

 case for natural selection, seem to have definitely disposed 

 of the only rival theory, the doctrine of Lamarck founded 

 on the supposed "inheritance of acquired characters." 

 Fortuitous changes in the inherited organisation are left 

 as the only elements of primary importance, the only 

 stones of which the edifice is built. 



Misunderstanding lies at the root of many of the ob- 

 jections urged against Darwinism. For instance, almost 

 every detractor of natural selection has brought forward 

 with wearisome reiteration the criticism that the theory 

 does not account for the origin of variations. Of course 

 it does not ; it was never meant to do so. No one has 

 tried to drive this point home more persistently than 

 Darwin himself : " Some have even imagined that natu- 

 ral selection induces variability, whereas it implies only 

 the preservation of such variations as arise ;"..." un- 

 less such occur natural selection can do nothing " (Origin 

 of Species). What selection alone can do is to preserve 

 these variations, and to pile one individual difference on 

 the top of another in the direction of adaptation, leading 

 to ever increasing changes along divergent lines. 



Another "criticism" is that natural selection is nov 

 the means whereby adaptation is brought about because 

 organisms must have the desired structure before ths^ 

 are chosen, must be preadapted. But if by adaptation 

 we merely mean the appearance of a favourable variation, 

 the statement amounts to an obvious truism. Further, 

 if by adaptation we merely mean that an organism has 

 such a structure that it will live, all living things are 



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