c iUp. VIII. 
SEXUAL SELECTION. 
297 
When variations occur late in life in one sex, and are 
transmitted to the same sex at the same age, the other 
s ex and the young are necessarily left unmodified. 
When they occur late in life, but are transmitted to 
koth sexes at the same age, the young alone are left un- 
modified. Variations, however, may occur at any period 
of life in one sex or in both, and be transmitted to both 
sp Xes at all ages, and then all the individuals of the 
species will be similarly modified. In the following 
chapters it will be seen that all these cases frequently 
°ccur under nature. 
Sexual selection can never act on any animal be- 
fore the age for reproduction has arrived. From 
the great eagerness of the male it has generally 
ac ted on this sex and not on the females. The males 
We thus become provided with weapons for fight- 
Ojg with their rivals, or with organs for discovering 
au d securely holding the female, or for exciting and 
charming her. When the sexes differ in these respects, 
] t is also, as we have seen, an extremely general law 
tl»at the adult male differs more or less from the young 
male; and we may conclude from this fact that the 
Recessive variations, by which the adult male became 
modified, have not generally occurred much before the 
for reproduction. Whenever some or many of the 
Variations have occurred early in liie, the young males 
"nil partake in a less or greater degree of the dia- 
meters of the adult males. Differences of this kind 
between the old and young males may be observed 
"ith many animals, for instance with birds. 
It is probable that young male animals have often 
tended to vaiy in a manner which would not only have 
Wn of no use to them at an early age, but would have 
men actually injurious,— as in the acquisition of bright 
e °lours, which would have rendered them conspicuous 
