CHAPTER XXVI 



THE MUTATION THEORY 



It will be recalled that Darwin, although depending upon the 

 ever-present fluctuating variations as the material for natural selection 

 to work upon, recognized the occasional occurrence of "sports" or 

 "saltatory variations." These, however, seemed to him to be so rare 

 in nature as to offer no adequate basis for selection. During the latter 

 part of the nineteenth century several investigators, feeling the 

 inadequacy of fluctuating variations to produce qualitatively new 

 characters, decided to make a more careful examination of animals 

 and plants in nature in order to discover whether saltatory variations 

 might not be of more frequent occurrence than Darwin had supposed. 



In England William Bateson collected a large number of instances 

 of a type of variation which he called discontinuous in contradistinc- 

 tion to the continuous type which we have been calling fluctuations. 

 Such variations, instead of being in a closely graded series with the 

 typical variations of a species, were frequently quite sharply different 

 from the majority. Although no experiments were conducted in 

 order to test the hereditability of these "discontinuous variations," 

 it is probable that some of them were "mutations" in the sense of 

 De Vries. 



At about the same time Hugo De Vries in Holland, partially as 

 the result of his rediscovery of Mendel's work and his confirmation of 

 the latter's laws of heredity, became convinced that new species arise 

 not by the accumulation, through natural selection, of minute fluc- 

 tuating variations, but by the sudden appearance in one generation 

 of fully formed new elementary species. He began a systematic 

 research for species of plants in nature that were giving rise to new 

 species. Many species were examined in their natural surroundings 

 and were then brought into the experimental garden for more careful 

 observation, but for a long time the search for a species throwing off 

 new elementary species was unsuccessful. Finally, however, in a 

 field near Hilversum, in the vicinity of Amsterdam, he found what 

 seemed to him to be just the kind of plant he had been looking for in 

 the evening primrose {Oenothera lamarckiana) . 



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