OTHER THEORIES OF EVOLUTION 347 



stresses the difficulty of explaining it by selection. The par- 

 ticular difficulty which it encounters is discussed in the 

 summary of the theories below. 



All these theories, which differ from one another in 

 many essentials, agree in one important feature. They 

 reject the mechanistic view of evolution and insist on the 

 spontaneity and self-sufficiency of life. Adaptation may 

 canalise the evolutionary impulse, but its potentialities and 

 their expression are implicit in life itself and are not pro- 

 duced by a blind sieving of variation, by the direct effect 

 of the environment, by the conscious will of the organism 

 or by chance. How are we to criticise this viewpoint ? In 

 particular, how are we to relate it to the mechanism of evolu- 

 tion of which we have some certainty, viz. its production by 

 increments of the order of mutations ? These theories are in 

 fact accounts of evolution as a whole, and not explanations of 

 the destiny of variations. Of the theories under discussion 

 only that of Smuts realises the obligation to supply an account 

 of the steps in evolution. If indeed forces such as we have 

 been considering are operative and evolution proceeds by 

 them, and not by selection or the direct action of the environ- 

 ment, the stages by which they express themselves would 

 have to be achieved in the same way as the spread of non- 

 adaptive mutations (p. 318). The transformations of popula- 

 tions which are evolving under the influence of such forces 

 would have to be brought about in exactly the same way as 

 we have discussed there. The fact is that all observations on 

 adaptation, the regulation of the life processes of the individual 

 and the occurrence of internal impulsions seem to demand 

 some means by which mutations may spread. 



