TRANSFORMISM 229 



selected increase in amount. Elimination of the 

 weakest occurs. The idea is eminently clear and 

 simple, and possesses a great degree of generality : 

 it is self-evident, says Driesch, meaning that it cannot 

 be refuted, for it was certainly not clearly obvious 

 to the naturalists before Darwin and Wallace. But, 

 unless we choose to be dogmatic, we can hardly claim 

 that it is an all-sufficient cause for the evolutionary 

 process, and it is useless to attempt to minimise the 

 difficulties of the hypothesis. It is not easy to make 

 it account for the origin of instincts or tropisms, or 

 for restitutions and regenerations of lost parts, or for 

 the appearance of the first non-functional rudiments 

 of organs which later become functional and useful. 

 It is, indeed, possible to devise plausible hypotheses 

 accounting for all these things in terms of natural 

 selection, but each such subsidiary hypothesis loads 

 the original one and weakens it to that extent. 



Natural selection does not, of course, induce or 

 evoke variations ; these are given to its activity, and 

 they are the material on which it operates. What, then, 

 is the nature of the deviations from the specific types 

 of morphology that are selected or eliminated ? Not 

 those induced by the environment, and transmitted in 

 their nature and direction to the progeny of the 

 organisms first displaying them. It is not unproved 

 that such variations do occur, and it is even probable 

 that they do occur. But we may conclude that the 

 frequency of their occurrence is not great enough to 

 afford sufficient material for natural selection. It is 

 also clear that the ordinarily occurring variations that 

 we observe in any large group of organisms collected 

 at random are not alone the material for selection ; 

 for we have seen that experimental breeding from such 

 variations does not lead to the establishment of a 



