96 DIVERGENCE OF CHARACTER. 



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 differences ; 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 witb 

 shorter and shorter beaks. Again, we may suppose thau 

 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- 

 ferior animals with intermediate characters, being neither 

 very swift nor very strong, would not have been used for 

 breeding, and will thus have tended to disappear. Here, 



