ARTIFICIAL SELECTION 



83 



have almost always small curved horns which are white, not 

 black, as in the still more primitive Irish breed. Most of these 

 distinctive traits offer neither advantages nor disadvantages 

 either to the sheep or its owner. They are nonadaptive or 



FIG. 48. Typical Dorset ewe, horned. (After Shaw.) 



FIG. 49. Polled Welsh sheep, a primitive type, lean and scant wooled. (After Youatt.) 



indifferent characters. These characters are therefore asso- 

 ciated with the hereditary traits of the original stock. They 

 are preserved through segregation and they are lost when herds 

 from different counties freely intermingle. Free interbreeding 

 would give a new and relatively uniform race of sheep over the 

 whole area occupied by these separate breeds. 



