98 THE LESSON OF EVOLUTION 



sufficiently strong to overcome all obstacles. The 

 greatest obstacle is free intercrossing with individuals 

 which do not possess the variation. This is over- 

 come, either 1 by the isolation of a few individuals, or 

 by a large number of individuals changing together in 

 the same direction, and so forming a group by them- 

 selves. This last is the necessary foundation of 

 Lamarckism ; and the term "determinate variation" 

 might be restricted to it , provided it was well under- 

 stood that determinate variation was only a special 

 form of definite variation. The first is the founda- 

 tion of modern Darwinism ; but that theory does not 

 exclude definite variation, or even that particular 

 form of it which we have just called determinate 

 variation, if it should be shown that such variations 

 can be transmitted from one generation to another. 

 Indeed, it is well known that Mr. Darwin allowed 

 far more influence to use-inheritance than the new 

 Darwinians are inclined to do. 



Discontinuous Variation. Another point to be 

 investigated is whether variations are continuous or 

 discontinuous. That is, are they small and 

 numerous, or are they large and abrupt, without any 

 intermediate links? 



The whole tendency of the experience of breeders 

 and horticulturists is in favour of continuous varia- 

 tion ; but several cases are known of the opposite. 

 These were called " Sports " by Darwin, who came 

 to the conclusion that they rarely originated new 

 species. Mr. Bateson, in his " Materials for the 

 study of Variations " (1894), takes exactly the oppo- 

 site view : namely, that the sports are the most 



