158 
LAWS OF VARIATION. 
Chap. V. 
the several species to their several places in the eco¬ 
nomy of nature, and likewise to fit the two sexes of the 
same species to each other, or to fit the males and 
females to different habits of life, or the males to 
struggle with other males for the possession of the 
females. 
Finally, then, I conclude that the greater variability 
of specific characters, or those which distinguish species 
from species, than of generic characters, or those which 
the species possess in common ;—that the frequent ex¬ 
treme variability of any part which is developed in a 
species in an extraordinary manner in comparison with 
the same part in its congeners ; and the slight degree 
of variability in a part, however extraordinarily it may 
be developed, if it be common to a whole group of spe¬ 
cies ;—that the great variability of secondary sexual 
characters, and the great amount of difference in these 
same characters between closely allied species;—that 
secondary sexual and ordinary specific differences are 
generally displayed in the same parts of the organisa¬ 
tion,—are all principles closely connected together. All 
being mainly due to the species of the same group hav¬ 
ing descended from a common progenitor, from whom 
they have inherited much in common,—to parts which 
have recently and largely varied being more likely still 
to go on varying than parts which have long been inhe¬ 
rited and have not varied,—to natural selection having 
more or less completely, according to the lapse of time, 
overmastered the tendency to reversion and to further 
variability,—to sexual selection being less rigid than 
ordinary selection,—and to variations in the same parts 
having been accumulated by natural and sexual selec¬ 
tion, and having been thus adapted for secondary sexual, 
and for ordinary specific purposes. 
