82 



EVOLUTION AND ANIMAL LIFE 



areas. In the beginning men are satisfied with sheep as sheep. 

 Little attention is paid to the distinction among individuals. 

 Those which are feeble, ill nourished, untamable, scant-fleeced, 

 or otherwise unfit will be eliminated, a process which will tend 

 to improve the stock, without giving the race distinctive quali- 

 ties, except as compared with the wild original. To form dis- 

 tinct races, the factor of isolation must enter. Those in one 

 county, for example, will be, at the beginning, somewhat 



different from those in an- 

 other. Each herd will show 

 its own traits in time, these 

 due primarily to differences 

 in the original stock, 

 secondarily to the pre- 

 dominance of one form of 

 variation over others. Ex- 

 changes of sheep will, by 

 cross-breeding, tend to 

 unify the type of sheep in 

 some one county, or on 

 some side of a barrier across 

 which sheep are not driven. 

 With this, there will be also 

 variations in the character 

 of the unconscious selec- 

 tion. One type of sheep 

 will flourish in a meadow 

 county, another on a moor, 

 and still another on the 

 rocky hills. At any rate, 

 as the environment varies, 

 so will the character of the 



selection. Thus as a final result, in Southern England, the 

 Southdown sheep of Sussex have tawny faces and legs; the 

 sheep of Hampshire have black faces, ears, and legs, with a 

 black spot under the tail; this black spot is lacking in the sheep 

 of Devon. In the Cheviot sheep the face and ears are white, the 

 head free from wool, while the ears, unlike those of most of the 

 others, stand erect. In the dun-faced Shropshire sheep, the 

 faces are more or less covered by wool. All these are hornless, 

 while the more primitive Dorset sheep with white face and ears 



FIG. 47. Silver-laced Wyandotte cockerel. 

 (After photograph.) 



