NATURAL SELECTION 19 



variations still shows a certain rather definite "species 

 mean," to which most of the variants rather closely conform, 

 but from which some considerably diverge. Mutation, ac- 

 cording to De Vries, establishes a new species with a new 

 species mean and a new series of fluctuating variations 

 gathered about the new mean. 



Similar phenomena have long been known to florists 

 and breeders of animals, the divergent individuals of the 

 new type having been called sports. To De Vries, how- 

 ever, belongs the credit of having studied these phenomena 

 in many thousands of individuals through many genera- 

 tions. Yet, careful and extensive as has been De Vries' 

 work, we cannot yet be assured that the appearance of 

 discontinuity in variation, by which new types are suddenly 

 established, is not due to insufficient observation, and that 

 the study of a still larger series of individuals would not 

 show forms completely bridging over the gap between the 

 old and new types. At present we can say only that De 

 Vries' work has shown the likelihood of there being a 

 real distinction between fluctuating variations and muta- 

 tions. Other features of De Vries' observations will be re- 

 ferred to later. 



The individuals of new character, arising by mutation, 

 must be subject to natural selection, and therefore those 

 which are not well adapted to their environment will be 

 destroyed, as in the case of divergent individuals arising 

 by fluctuating variation. 



Referring again to the illustration given above, ob- 

 serve that all the rabbits in the given region are sub- 

 ject to natural selection and the more perfectly adapted 

 individuals will be preserved. It makes no difference 



