CHAPTER V 



THE THEORY OF MUTATION 



MUTATION is the term applied by de Vries to express 

 the process of origination of a new species, or of a new 

 specific character, when this takes place by the dis- 

 continuous method at a single step a process which 

 he regards as the most important if not the sole 

 method by which new species or specific characters 

 arise. We shall see that although de Vries has 

 recently done much to forward the propagation of 

 this idea, the belief that such a discontinuous process 

 is the normal method by which new species come into 

 existence has been developing for a considerable time. 

 We have seen that those who accept the idea of 

 evolution by the action of natural selection upon a 

 series of minute and almost imperceptible variations 

 are confronted with the difficulty of explaining how 

 by this method there could arise a number of different 

 structures or parts so co-ordinated as to share in a 

 common function. Moreover, a closer examination 

 of the actual processes of variation and inheritance 

 render it doubtful whether the selection of continuous 

 variations of even a simple character can ever lead to 

 the development of a permanent new race. The 



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