l84 THE FOUNDATIONS OF ZOOLOGY 



by the preservation and accumulation of small inherited modifica- 

 tions, each profitable to the preserved being." This has seemed, 

 and still seems, to many, a valid reason for questioning its value 

 as a scientific explanation of the origin of species ; although no 

 one who makes Darwin's words an occasion of his own thinking 

 need be perplexed by this criticism. If peas are rolled down an 

 inclined board, the largest go fastest, the smallest slowest, and the 

 round ones go straight to the bottom, while the irregular ones run 

 off the sides. What if one were to assert that this device can have 

 no value as a means for sorting peas until we know what makes 

 one pea large and another small, one round and another irregular ? 

 Yet this is, in effect, asserted by those who declare that natural 

 selection has no value as an explanation of the origin of species, 

 because it does not show why there should be anything useful to 

 select. Without knowing why one horse is more fleet than another, 

 or even why horses exist, breeders have increased the speed of 

 horses by breeding from the most fleet; just as a pack of wolves 

 may increase it in nature by destroying, generation after genera- 

 tion, all the horses they can run down. If at every stage in the 

 ancestry of horses there has been need for greater speed, natural 

 selection accounts for the whole history of this power, and even 

 for the first vague beginnings of locomotion in sedentary or float- 

 ing animals, which may have found shelter from their enemies, 

 or more abundant food, by those slight changes of place which 

 may, at first, have been the incidental result of changes of 

 shape. 



While it is obvious that a useful quality must exist before it 

 can be useful, and before it can be influenced by selection, and 

 while no Darwinian holds natural selection to be an ultimate ex- 

 planation of fitness, all admit that horses do differ among them- 

 selves in speed, and that each may reasonably be expected to be 

 more like its parents in speed than like a horse selected at random. 

 As no one disputes the existence of these prerequisites to selec- 

 tion, the statement that selection could not act unless they existed 

 is childish. 



I have tried to show, page 178, that the work of Darwin and 

 Wallace teaches that the only path in which we can have any well- 

 founded hope of progress in the explanation of the origin of species 



