ORIGIN OF THE LIVING MACHINE: ADAPTATION 357 



The Mutation Theory. One of the essential factors of the 

 Darwinian theory was that the change of species was produced 

 by the selection of minute diversities, such as the slight differ- 

 ences found among animals and plants of the same species. It 

 was argued by Darwin that in the struggle for existence, when 

 the majority must be exterminated that the few may live, even 

 the slightest differences in structure, shape, body, color, or habits 

 would be sufficient to determine the question of life or death. 

 If these slight differences could accumulate, generation after 

 generation, they would in time become great; and thus, accord- 

 ing to Darwin, the great differences between type were produced 

 by the accumulation and heaping up of minute variations. To 

 many of the more recent students of this subject it has not 

 seemed plausible that such minute differences could accomplish 

 all that Darwin claimed for them. Many objections to Darwin's 

 ideas on this line have been expressed, and have finally found 

 voice in a more recent conception of the conditions which have 

 produced the evolution of the living world. This new idea is the 

 mutation theory (Lat. mutare = to change), and is commonly 

 associated with the Dutch naturalist, DeVries, although a num- 

 ber of others have shared in its origin and development. DeVries 

 based his views upon observations made in a field of primroses, 

 where he kept thousands of individuals under observation. 

 As the result of these observations, he came to the conclusion 

 that new types of plants are appearing constantly in nature; 

 but that they do not arise, as Darwin had supposed, by the accu- 

 mulation of little changes one generation after another, but 

 suddenly, and, as a rule, in single steps. In his field of primroses, 

 growing side by side, he found several distinct types, abso- 

 lutely different from each other and with no intermediate 

 steps between them. They came, not as the result of the ac- 

 cumulation of little steps, but suddenly, in a single generation. 

 Moreover, by isolating and experimenting with them, he found 

 that the new characters, which had thus appeared, bred true, 

 i. e., remained fixed in the race. 



