The Making of Species 
may indirectly be responsible for characteristics 
which in themselves are injurious to the in- 
dividual. This is probably the case as regards 
the decorative plumage of some male birds. 
The phenomenon of correlation was recognised 
by Darwin, and has, we believe, played an 
important part in the making of species. We 
shall deal more fully with the subject in a later 
chapter. 
5. An oft-urged objection to the theory of natural 
selection, and one which weighed very strongly 
with Huxley, is that breeders have hitherto not 
succeeded in breeding a variety which is infertile 
with the parent species. If, Huxley asked, 
breeders cannot produce such a thing, how 
can we say we consider it proved that natural 
selection produces new species in nature? This 
objection, however, loses much of its force in 
view of the fact that many perfectly distinct 
species are quite fertile when bred together. We 
shall recur to this in Chapter IV. 
6. The fact that paleontology has hitherto failed 
to yield links connecting many existing species is 
a classical objection to the theory of the origin 
of species by gradual evolution. 
Wallace states this objection as follows, on 
page 376 of his Darwinism: ‘‘Many of the 
gaps that still remain are so vast that it seems 
incredible to these writers that they could ever 
have been filled up by a close succession of 
4o 
