CHAP. VI 
DIFFICULTIES AND OBJECTIONS 
127 
grounds for the objection above made, that such small and 
slight variations could be of no real use, and would not 
determine the survival of the individuals possessing them. AVe 
have seen, however, in our third chapter, that even Darwin’s 
terms were hardly justified; and that the variability of many im¬ 
portant species is of considerable amount, and may very often 
be properly described as large. As this is found to be the 
case both in animals and plants, and in all their chief groups 
and subdivisions, and also to apply to all the separate parts 
and organs that have been compared, we must take it as 
proved that the average amount of variability presents no 
difficulty whatever in the way of the action of natural selection. 
It may be here mentioned that, up to the time of the prepara¬ 
tion of the last edition of The Origin of Species, Darwin had 
not seen the work of Mr. J. A. Allen of Harvard University 
(then only just published), which gave us the first body of accu¬ 
rate comparisons and measurements demonstrating this large 
amount of variability. Since then evidence of this nature 
has been accumulating, and we are, therefore, now in a far 
better position to appreciate the facilities for natural selection, 
in this respect, than was Mr. Darwin himself. 
Another objection of a similar nature is, that the chances 
are immensely against the right variation or combination of 
variations occurring just when required; and further, that no 
variation can be perpetuated that is not accompanied by 
several concomitant variations of dependent parts—greater 
length of a wing in a bird, for example, would be of little use 
if unaccompanied by increased volume or contractility of the 
muscles which move it. This objection seemed a very strong 
one so long as it was supposed that variations occurred singly 
and at considerable intervals ; but it ceases to have any weight 
now we know that they occur simultaneously in various parts 
of the organism, and also in a large proportion of the in¬ 
dividuals which make up the species. A considerable number 
of individuals will, therefore, every year possess the required 
combination of characters; and it may also be considered 
probable that when the two characters are such that they 
always ad together, there will be such a correlation between 
them that they will frequently vary together. But there is 
another consideration that seems to show that this coincident 
