ORGANIC POLARITY AND MUTATION 111 



experience goes, they occur at random — that is, in the most diverse 

 directions." 



"The new species is at once such, and originates from the former 

 species without apparent preparation and without graduation. 

 Each attribute, of course, arises from one previously present, not 

 by their normal variation, but by one small yet sudden change. 

 Provisionally one may compare these changes, but only in the 

 simplest manner, with chemical substitution." 



Then in regard to the Darwinian view that "species have 

 originated by natural selection in the struggle for existence," he 

 says, " whenever the contest occurs between individuals of one and 

 the same elementary species, it also occurs between the different 

 species as such. The first-mentioned contest pertains to the 

 doctrine of variability, the second to that of mutation. In the first- 

 mentioned case those individuals survive which find their life 

 conditions most favourable, and they are therefore generally the 

 most vigorous. By this process local races originate, and by it 

 acclimatisation is made possible. If the new life conditions cease, 

 then the adapted races revert to the original type. . . . Natural 

 selection in the struggle for existence between the newly originated 

 elementary species is quite different. These originate suddenly, 

 unmediated, and multiply themselves if nothing stands in the way, 

 because they are for the most part completely, or in a high degree, 

 heritable. If then the increase leads to a struggle for existence, 

 the weaker succumb and are rooted out. According as the older or 

 the younger form happens to be the better suited for the life 

 conditions will one or the other survive. . . . The contest decides 

 which of them shall survive and which shall perish. These 'species 

 selections,' in the course of their evolution, have, without doubt, 

 rooted out immense numbers and retained only a small proportion. 

 Briefly stated, I assert, of course on the ground of the mutation 

 theory, that by the struggle for existence and natural selection 

 species do not originate, but perish." 



As a factor in Evolution, therefore, it is clear that the 'mutation' 

 theory of de Vries is intended by its author actually to replace the 

 theory of 'natural selection.' To what extent it will do so cannot 

 be decided till much additional work has been done and many 

 years have elapsed. In many respects his views are in accord 

 with those of Cope, Packard, and Hyatt already referred to. 



De Vries beUeves that all species and genera, while always 

 subject to the full range of fluctuating variability, exist at 



