NATURAL SELECTION 101 



(I quote the words of an agricultural writer) { as if by 

 some murderous pestilence.' 



Divergence of Character. — The principle, which I have 

 designated by this term, is of high importance on my 

 theory, and explains, as I believe, several important 

 facts. In the first place, varieties, even strongly- 

 marked ones, though having somewhat of the character 

 of species — as is shown by the hopeless doubts in many 

 cases how to rank them — yet certainly differ from each 

 other far less than do good and distinct species. Never- 

 theless, according to my view, varieties are species in 

 the process of formation, or are, as I have called them, 

 incipient species. How, then, does the lesser difference 

 between varieties become augmented into the greater 

 difference between species ? That this does habitually 

 happen, we must infer from most of the innumerable 

 species throughout nature presenting well-marked differ- 

 ences ; whereas varieties, the supposed prototypes and 

 parents oTTuture well-marked species, present slight 

 and ill-defined differences. Mere chance, as we may 

 call it, might cause one variety to differ in some char- 

 acter from its parents, and the offspring of this variety 

 again to differ from its parent in the very same character 

 and in a greater degree ; but this alone would never 

 account for so habitual and large an amount of differ- 

 ence as that between varieties of the same species and 

 species of the same genus. 



As has always been my practice, let us seek light on 

 this head from our domestic productions. We shall 

 here find something analogous. A fancier is struck 

 by a pigeon having a slightly shorter beak ; another 

 fancier is struck by a pigeon having a rather longer 

 beak ; and on the acknowledged principle that ' fanciers 

 do not and will not admire a medium standard, but 

 like extremes,' they both go on (as has actually occurred 

 with tumbler-pigeons) choosing and breeding from birds 

 with longer and longer beaks, or with shorter and 

 shorter beaks. Again, we may suppose that at an 

 early period one man preferred swifter horses ; another 



