XIV THE ORIGIN OF SPECIES AND GENERA 289 



Darwin has himself admitted that there are these unknown 

 causes at work, and that " natural selection is the most 

 important but not the exclusive means of modification." 

 There may be some question as to the term " most im- 

 portant," if, as is not improbable, the most radical differ- 

 ences in animals and their most important organs could 

 not have been produced by it alone in the same way as 

 the specific modifications of a genus or family may be 

 produced. This, however, is a ftiir matter for discussion 

 and research, and will probably continue to be so for 

 many generations ; and even if it should be ever proved 

 that higher laws than " natural selection " have brought 

 about the more fundamental divergences of the animal 

 and vegetable kingdoms, this will not be held to detract 

 in any way from the greatness and the value of Mr. 

 Darwin's work, any more than it will be held to detract 

 from the greatness of Newton, if it should some day be 

 demonstrated that the law of gravitation as expressed by 

 him is not absolutely true, but that (as some physicists 

 now suppose) it should be found to be subject to a higher 

 law for remote stellar distances, or in the case of such 

 exceptional phenomena as those presented by comets. 



No thoughtful person can contemplate without amaze- 

 ment the phenomena presented by the development of 

 animals. We see the most diverse forms — a mollusc, a 

 frog, and a mammal — arising from apparently identical 

 primitive cells, and progressing for a time by very similar 

 initial changes, but thereafter each pursuing its highly 

 complex and often circuitous course of development, Avith 

 unerring certainty, by means of laws and forces of which 

 we are almost totally ignorant. It is surely a not im- 

 probable supposition that the unkno^vn power which 

 determines and regulates this marvellous process may also 

 determine the initiation of those more important changes 

 of structure and those developments of new parts and 

 organs which characterise the successive stages of the 

 evolution of animal forms. In so far as Mr. Darwin denies 

 the necessity of any such power, and maintains that the 

 origin of all the diverse fotms and types and all the 

 complex structures of the organic world are due to identi- 

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