Criticisms of Theory of Natiiral Selection. 347 



human species furnishes the worst example that could 

 have been chosen. 



Hitherto I have been consldeiing objections which 

 arise from misapprehensions of Darwin's theory. I 

 will now go on to consider a logically sound ob- 

 jection, which nevertheless is equally futile, because, 

 although it does not depend on any misapprehension 

 of the theory, it is not itself supported by fact. 



The objection is the same as that which we have 

 already considered in relation to the general theory of 

 descent — namely, that similar organs or structures 

 are to be met with in widely different branches of the 

 tree of life. Now this would be an objection fatal to 

 the theory of natural selection, supposing these organs 

 or structures in the cases compared are not merely 

 analogous, but also homologous. For it would be 

 incredible that in two totally different lines of descent 

 one and the same structure should have been built up 

 independently by two parallel series of variations, and 

 that in these two lines of descent it should always and 

 independently have ministered to the same function. 

 On the other hand, there would be nothing against 

 the theory of natural selection in the fact that two 

 structures, ;/(?/ homologous, should come by inde- 

 pendent variation in two different lines of descent to 

 be adapted to perform the same function. For it 

 belongs to the very essence of the theory of natural 

 selection that a useful function should be secured by 

 favourable variations of whatever structural material 

 may happen to be presented by different organic 

 t}'pes. Flying, for instance, is a very useful function, 

 and it has been developed independently in at least 



