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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. 
. . . 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. . . . 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.”—(Darwin and After Darwin, fp. 286-7.) 
It might seem a simple act of prudence to leave un 
noticed so powerful an argument as this; and bearing 
in mind the warning that “ fools rush in where angels fear 
to tread,” it might be well to give up an attempt which no 
one has been rash enough to make. But if this un 
answered challenge constitutes “ a general consideration of 
the largest possible significance in the present connection,” 
one would have supposed that the advocates of the theory 
would have frequently employed so powerful an argument. 
But curiously enough it is not so. Mr. Romanes says :— 
“ It is somewhat remarkable that the enormous importance of this 
argument in favour of Natural Selection as a prime factor of organic 
evolution has not received the attention which it deserves. Even 
Darwin himself, with his characteristic reserve, has not presented its 
incalculable significance, nor do I know any of his followers who have 
made any approach to an adequate use of it in their advocacy of his 
views.”—(.Darwin and After Day win. pp. 291-2.) 
That the opponent should avoid and ignore an argument 
of so much importance—an argument which, it might be 
assumed, he could not answer satisfactorily—is intelligible 
enough ; but that the advocate should hesitate to use such 
an argument is simply astonishing, when we consider the 
very great acumen, sometimes almost amounting to genius, 
which characterises those who have defended this theory. 
Let us see if there are any reasons why this strong 
argument has not been employed.