324 THE THEORIES OF EVOLUTION 



"Paragraphs 3 and 4 point out obstacles to this 

 possible intercrossing which are as real in fluctuating 

 variation as in mutation. 



"Paragraphs 5 and 6, relative to indifferent or even 

 slightly injurious characters, establish a fact which is 

 not accounted for by mutation any more than by 

 natural selection, the origin of variations. Both the- 

 ories simply take them for granted. Neither in fluc- 

 tuation nor in mutation, do isolated variations have 

 any importance; what really counts is plural varia- 

 tions which are more likely to occur in fluctuation than 

 in mutation." 5 



Many other arguments have been presented by va- 

 rious authors for or against (more for than against), 

 the theory of mutation, but we shall not refer to them. 

 The claims sometimes made that the new doctrine 

 furnished a general explanation of phylogenetic evo- 

 lution and could supersede all other hypotheses is not 

 well founded. The theory of mutation only points 

 out one of the various lines followed by evolution. 

 That evolution may follow this line is amply proved 

 by De Vries' many and accurate experiments. 



In one respect the new theory appears unsatisfac- 

 tory: it does not account in any way for the general 

 and important phenomenon of adaptation. De Vries 

 does not seem to have attached any importance to this 



s L. Plate. Darwinism us contra Mutationstheorie, quoted in German 

 in V. L. Kellogg, Darwinism To-day, pp. 368-372. 



