103 DIVERGENCE OF OHABACTEB. 



species. Nevertheless 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 differ- 

 ence 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 of future well-marked species, present slight and 

 ill-defined differences. Mere chance, as we may call it, 

 might cause one variety to differ in some character 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 a degree of difference as that between the species 

 of the same genus. 



As has always been my practice, I have sought light on 

 this head from our domestic productions. We shall here 

 find something analogous. It will be admitted that the 

 production of races so different as short-horn and Here- 

 ford cattle, race and cart horses, the several breeds of 

 pigeons, etc., could never have been effected by the mere 

 chance accumulation of similar variations during many 

 successive generations. In practice, a fancier is, for in- 

 stance, 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 

 the sub-breeds of the tumbler-pigeon) choosing and breed- 

 ing from birds with longer and longer beaks, or with 

 shorter and shorter beaks. Again, we may suppose that 

 at an early period of history, the men of one nation or dis- 

 trict required swifter horses, while those of another re- 

 quired stronger and bulkier horses. The early differences 

 would be very slight; but, in the course of time, from the 

 continued selection of swifter horses in the one case, and 

 of stronger ones in the other, the differences would become 

 greater, and would be noted as forming two sub-breeds. 

 Ultimately after the lapse of centuries, these sub-breeds 

 would become converted into two well-established and dis- 

 tinct breeds. As the differences became greater, the in- 



