VII 



THE COW TEIBES 



In those far-off centuries when herds of wild 

 cattle ranged through the forests of northern 

 Europe, the individuals were presumably very 

 much alike in type, size, and color markings. It 

 seems to be a law of biology that when any species 

 of plant or animal exists for a long period of time 

 under an unchanging environment, a general uni- 

 formity of type results. For example, among wild 

 deer, the American bison, robins, chipmunks or 

 woodchucks, with rare exceptions, every individual 

 of a species is so like every other member that one 

 exact zoological description suffices for all. On 

 the other hand, when the environment, or the daily 

 life conditions, is changed, immediately the ten- 

 dency to mutations is exhibited, the appearance of 

 individuals possessing new or unusual characters. 

 The cow has been wonderfully altered under do- 

 mestication, partly because new traits and charac- 

 ters have come unconsciously in response to new 

 surroundings, partly because her master and 

 owner has encouraged and preserved these new 

 developments by keeping and rearing especially 



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