Evidences of Theory of Natural Selection. 287 



be proved to be of exclusive use to any species other 

 than the one presenting it. He even went so far as to 

 say that if any one such instance could be shown he 

 would surrender his whole theory on the strength of 

 it so assured had he become, by his own prolonged 

 researches, that natural selection was the true agent 

 in the production of adaptive structures, and, as such, 

 could never have permitted such a structure to occur 

 in one species for the benefit of another. Now, as this 

 invitation has been before the world for so many years, 

 and has not yet been answered by any naturalist, we 

 may by this time be pretty confident that it never will 

 be answered. How tremendous, then, is the significance 

 of this fact in its testimony to Darwin's theory ! The 

 number of animal and vegetable species, both living 

 and extinct, is to be reckoned by millions, and every 

 one of these species presents on an average hundreds of 

 adaptive structures, at least one of which in many, 

 possibly in most, if not actually in all cases, is peculiar 

 to the species that presents it. In other words, there 

 are millions of adaptive structures (not to speak of in- 

 stincts) which are peculiar to the species presenting 

 them, and also many more which are the common 

 property of allied species : yet, notwithstanding this 

 inconceivable profusion of adaptive structures in 

 organic nature, there is no single instance that has 

 been pointed out of the occurrence of such a structure 

 save for the benefit of the species that presents it. 

 Therefore, I say that this immensely large and general 

 fact speaks with literally immeasurable force in favour 

 of natural selection, as at all events one of the main 

 causes of organic evolution. For the fact is precisely 

 what we should expect if this theory is true, while 



