l68 THE FOUNDATIONS OF ZOOLOGY 



sufficient. Not only is it impossible to substantiate a claim for 

 natural selection that it is the sole agent in forming genera, but 

 it seems, from the experience of artificial selection, that it is 

 scarcely competent to do so by favoring mere varieties in the 

 sense in which I understand the term. Mere varieties from a 

 common typical centre blend freely in the offspring, and the off- 

 spring of every race where statistical characters are constant, neces- 

 sarily tend, as I have shown, to regress toward their common 

 typical centre. A mere variety can never establish a sticking 

 point in the forward course of evolution." 



Gallon therefore holds that, while specific stability is due to 

 inheritance from a long line of ancestors, the transmutation of 

 species is due to the sudden appearance of "sports," which, if use- 

 ful, are seized upon and perpetuated by selection. 



He says that a sport is a substantial change of type effected 

 by a number of small changes of typical centre, each more or less 

 stable, and each being in its turn favored and established by natural 

 selection to the exclusion of its competitors. 



"The distinction between a mere variety and a sport is real 

 and fundamental." 



This generalization, based upon numerical data, is so funda- 

 mental and far-reaching that a critical discussion of the evidence 

 is most important. 



