III PROTECTIVE RESEMBLANCES AMONG ANIMALS 35 
which it brought to light and made use of. The series of 
Natural History volumes in Lardner’s Cabinet Cyclopedia, in 
which Mr. Swainson developed it in most departments of the 
animal kingdom, made it widely known ; and in fact for a 
long time these were the best and almost the only popular 
text-books for the rising generation of naturalists. It was 
favourably received too by the older school; which was per- 
haps rather an indication of its unsoundness. A considerable 
number of well-known naturalists either spoke approvingly of 
it, or advocated similar principles, and for a good many years 
it was decidedly in the ascendant. With such a favourable 
introduction, and with such talented exponents, it must have 
become established if it had had any germ of truth in it; 
yet it quite died out in a few short years; its very existence 
is now a matter of history ; and so rapid was its fall that 
its talented creator, Swainson, perhaps lived to be the last 
man who believed in it. . 
Such is the course of a false theory. That of a true one 
is very different, as may be well seen by the progress of 
opinion on the subject of Natural Selection. In less than 
eight years The Origin of Species has produced conviction 
in the minds of a majority of the most eminent living men 
of science. New facts, new problems, new difficulties as they 
arise are accepted, solved, or removed by this theory ; and its 
principles are illustrated by the progress and conclusions of 
every well established branch of human knowledge. It is the 
object of the present chapter to show how it has recently been 
applied to connect together and explain a variety of curious 
facts which had long been considered as inexplicable anomalies. 
Importance of the Principle of Utility 
Perhaps no principle has ever been announced so fertile in 
results as that which Mr. Darwin so earnestly impresses upon 
us, and which is indeed a necessary deduction from the 
theory of Natural Selection, namely—that none of the 
definite facts or organic nature, no special organ, no char- 
acteristic form of marking, no peculiarities of instinct or of 
habit, no relations between species or between groups of 
species—can exist, but which must now be or once have been 
useful to the individuals or the races which possess them. 
