The Descent of Man

not more strange than that the tails of many
birds should be especially decorated.
With mammals we do not at present possess
any evidence that the males take pains to display
their charms before the female; and the
elaborate manner in which this is performed by
male birds and other animals is the strongest
argument in favour of the belief that the females
admire, or are excited by, the ornaments
and colours displayed before them. There is,
however, a striking parallelism between mammals
and birds in all their secondary sexual
characters, namely in their weapons for fighting
with rival males, in their ornamental appendages,
and in their colours. In both classes,
when the male differs from the female, the
young of both sexes almost always resemble
each other, and in a large majority of cases resemble
the adult female. In both classes the
male assumes the characters proper to his sex
shortly before the age of reproduction; and if