64 CREATIVE EVOLUTION CHAP. 



finitely complex eye of the vertebrates, it may just as 

 well be alleged that the result has been brought about 

 by natural selection perfecting the organ automatically. 

 In short, if there is a case in which it seems justifiable 

 to invoke adaptation, it is this particular one. For 

 there may be discussion about the function and mean 

 ing of such a thing as sexual generation, in so far as 

 it is related to the conditions in which it occurs ; but 

 the relation of the eye to light is obvious, and when 

 we call this relation an adaptation, we must know what 

 we mean. If, then, we can show, in this privileged 

 case, the insufficiency of the principles invoked on both 

 sides, our demonstration will at once have reached a 

 high degree of generality. 



Let us consider the example on which the advocates 

 of finality have always insisted : the structure of such 

 an organ as the human eye. They have had no diffi 

 culty in showing that in this extremely complicated 

 apparatus all the elements are marvellously co 

 ordinated. In order that vision shall operate, says the 

 author of a well-known book on Final Causes, &quot; the 

 sclerotic membrane must become transparent in one 

 point of its surface, so as to enable luminous rays to 

 pierce it . . . ; the cornea must correspond exactly 

 with the opening of the socket . . . ; behind this 

 transparent opening there must be refracting media 

 . . . ; there must be a retina 1 at the extremity of the 

 dark chamber . . . ; perpendicular to the retina there 

 must be an innumerable quantity of transparent cones 

 permitting only the light directed in the line of their 

 axes to reach the nervous membrane,&quot; 2 etc. etc. In 

 reply, the advocate of final causes has been invited to 



1 Paul Janet, Les Causes finales, Paris, 1876, p. 83. 

 2 Ibid. p. 80. 



