294 The Morality of Nature 



tions of disuse. These abilities of animals are acquired as 

 the product of needs, and are in evolution sustained by the 

 same causes which made them, only to be relinquished when 

 they cease to be useful. The flight of the pigeon and the 

 speed of the horse we see year by year increasing even be- 

 yond nature's standard as man's urging permeates the in- 

 centive. And as they can be developed, so too we know 

 the cow could be evolved into the fleeter type of its wild 

 stock, if man or nature made it advantageous to its racial 

 life, and so we know the hen and the farm duck could be 

 bred into strong flying fowls, if such habits were demanded 

 as necessary to fitness. 



The most notable effects of evolutionary changes under 

 the special influence of man are perhaps seen in the amazing 

 variation of the dog. Animals of this species vary in size 

 at least a hundred fold, yet the dog of a pound weight and 

 another of a hundred pounds, are of the same fundamental 

 type, and preserve biological likeness as creatures of one 

 original stock, although they have reached such differences 

 that cross breeding is impossible. But this question of cross 

 breeding is no longer an acceptable means of defining dif- 

 ference of species. Many different species, as by man 

 classified, can breed together, and have fertile progeny; and 

 many specimens of admittedly single species cannot. The 

 fact is that fertility in sexual union as a test of species, 

 indicates a newer classification, and does not aid the old 

 methods. Many so called different species merge one into 

 the other imperceptibly; and others, where the differences 

 are perceptible, a link which has become extinct, has pre- 

 viously connected them. The similarities of certain sheep 



