XVII THE METHOD OF ORGANIC EVOLUTION 353 



It is therefore necessary to give some account of the 

 nature of the facts themselves, as well as of the particular 

 theories they are held to support. 



Darwin distinguished two classes of variations, which 

 he termed " individual differences " and " sports." The 

 former are small but exceedingly numerous, the latter 

 large but comparatively rare, and these last are the 

 " discontinuous variations " of Mr. Bateson to which re- 

 ference has been already made. Darwin, while always 

 believing that individual differences played the most 

 important part in the origin of species, did not altogether 

 exclude sports or discontinuous variations, but he soon 

 became convinced that these latter were quite unim- 

 portant, and that they rarely, if ever, served to originate 

 new species ; and this view is held by most of his 

 followers. Mr. Bateson, however, seems to believe that 

 the exact contrary is the fact, and that sports or dis- 

 continuous variations are the all-important, if not the 

 exclusive, means by which the organic world has been 

 modified. Such a complete change of base as to the 

 method of organic evolution deserves, therefore, to be 

 considered in some detail. 



The difficulty which seems to have struck Mr. Bateson 

 most, and which he declares to be of " immense sig- 

 nificance," is, that while specific forms of life constitute a 

 discontinuous series, the diverse environments on which 

 these primarily depend shade into each other insensibly, 

 and form a continuous series {j>. 5). Further on, this 

 objection is again urged in stronger language : " We have 

 seen that the differences between Species are Specific, 

 and are differences of kind, forming a discontinuous Series, 

 while the diversities of environment to which they are 

 subject are on the whole differences of degree, and form a 

 continuous Series ; it is therefore hard to see how the en- 

 vironmental differences can thus be in any sense the 

 directing cause of Specific differences, which by the Theory 

 of Natural Selection they should be" (p. 16). Again, at 

 p. 69, he urges that the essential character of species is 

 that they constitute a discontinuous series, and he asks — 

 " Is it not then possible that the Discontinuity of Species 



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