ARTIFICIAL SELECTION 107 



new range of natural selection. Adaptive characters change 

 rapidly, and in ways more or less parallel, with similar altera- 

 tions in related species. Characters nonadaptive, often slight 

 in appearance and bearing no relation to the life of the animal, 

 become slowly but surely fixed as characters of the species. 

 As two closely allied breeds of animals are never found in the 

 same region unless purposely restrained from free interbreeding, 

 so two closely related species never develop in the same breeding 

 area. As the nearest relative of some given breed of domestic 

 animals is found in a given region nearly related geographically, 

 so is the nearest relative to any given wild species found, in 

 most cases, not far away. It is to be looked for on the other 

 side of some geographic, topographic, or climatic barrier. In 

 other words, the interrelation of variation, heredity, geographic 

 isolation and environmental features generally seems to be the 

 same in the formation of domestic races as in that of the 

 formation of natural species. The principal new element intro- 

 duced in the art of selective breeding is that of purposeful 

 crossing, the removal of the barriers which separate well- 

 differentiated forms, for the purpose of beginning a new series 

 to be selected toward a predetermined end. 



It has been recently repeatedly stated that most races of 

 domesticated animals or plants find their origin in a mutation 

 or saltation of some sort. In our judgment, there is not suffi- 

 cient evidence to prove this view. There are few cases of 

 either races or species known to have originated in this way. 

 That such is in fact the general law of race or species origin, 

 we see little reason to believe. One of the few well-known 

 illustrations of race-forming through saltation is that of the 

 Ancon sheep. In 1791, in Massachusetts, a ram was born with 

 unusually short legs. As this character was useful, preventing 

 the sheep from leaping over stone walls, the owner of this sheep 

 used the ram for breeding purposes, and succeeded in isolating 

 a short-legged strain of sheep known as the Ancon sheep. So 

 far as known to us, this type of sheep differed in this character 

 alone from the common sheep of Connecticut. With the later 

 advent of the more heavy-wooled, and therefore more profitable, 

 Merino, the Ancon sheep disappeared. A recent similar case of 

 race origin from a prepotent sport is that of the polled Here- 

 fords arising in Kansas from a hornless Hereford bull. 



