Chap. VIII. 
SEXUAL SELECTION. 
287 
and developed in the adult males alone. When, on the 
other hand, the adult male closely resembles the young 
of both sexes (these, with rare exceptions, being alike), 
he generally resembles the adult female ; and in most of 
these cases the variations through which the young and 
old acquired their present characters, probably occurred 
in conformity with our rule during youth. But there is 
here room for doubt, as characters are sometimes trans- 
ferred to the offspring at an earlier age than that at 
which they first appeared in the parents, so that the 
parents may have varied when adult, and have trans- 
ferred their characters to their offspring whilst young. 
There are, moreover, many animals, in which the two 
sexes closely resemble each other, and yet both differ 
from their young ; and here the characters of the adults 
must have been acquired late in life ; nevertheless, 
these characters in apparent contradiction to our rule, 
are transferred to both sexes. We must not, however, 
overlook ‘the possibility or even probability of succes- 
sive variations of the same nature sometimes occurring, 
under exposure to similar conditions, simultaneously in 
both sexes at a rather late period of life ; and in this case 
the variations would be transferred to the offspring of 
both sexes at a corresponding late age ; and there would 
be no real contradiction to our rule of the variations 
which occur late in life being transferred exclusively to 
the sex in which they first appeared. This latter rule 
seems to hold true more generally than the second rule, 
namely, that variations which occur in either sex early 
in life tend to be transferred to both sexes. As it was 
obviously impossible even to estimate in how large a 
number of cases throughout the animal kingdom these 
two propositions hold good, it occurred to me to inves- 
tigate some striking or crucial instances, and to rely 
on the result. 
