Criticesms of Theory of Natural Selection. 247 
human species furnishes the worst example that could 
have been chosen. 
Hitherto I have been considcting 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, zo¢ homologous, should come by inde- 
pendent variation in two different lines of descent to 
be adaptcd to perform the same function. For it 
belongs to the very essence of the theory of natural 
selection that a uscful function should be secured by 
favourable variations of whatever structural material 
may happen to be presented by different organic 
types. Flying. for instance, is a very uscful function, 
and it has been developed independently in at least 
