80 
NATURAL SELECTION. 
Chap. IV. 
CHAPTEE IV. 
Natukal Selection. 
Natural Selection — its power compared with man’s selection — its 
power on characters of trifling importance—its power at all ages 
and on both sexes—Sexual Selection—On the generality of inter¬ 
crosses between individuals of the same species — Circumstances 
favourable and unfavourable to Natural Selection, namely, 
intercrossing, isolation, number of individuals—Slow action— 
Extinction caused by Natural Selection — Divergence of Cha¬ 
racter, related to the diversity of inhabitants of any small area, 
and to naturalisation — Action of Natural Selection, through 
Divergence of Character and Extinction, on the descendants from 
a common parent—Explains the Grouping of all organic beings. 
How will tlie struggle for existence, discussed too briefly 
in the last chapter, act in regard to variation? Can 
the principle of selection, which we have seen is so 
potent in the hands of man, apply in nature ? I think 
we shall see that it can act most effectually. Let it be 
borne in mind in what an endless number of strange 
peculiarities our domestic productions, and, in a lesser 
degree, those under nature, vary; and how strong the 
hereditary tendency is. Under domestication, it may be 
truly said that the whole organisation becomes in some 
degree plastic. Let it be borne in mind how infinitely 
complex and close-fitting are the mutual relations of all 
organic beings to each other and to their physical con¬ 
ditions of life. Can it, then, be thought improbable, 
seeing that variations useful to man have undoubtedly 
occurred, that other variations useful in some way to 
each being in the great and complex battle of life, 
should sometimes occur in the course of thousands of 
generations ? If such do occur, can we doubt (remem- 
