The Descent of Man

the adults—On the increase of beauty in the
birds of the world—Protective colouring—
Conspicuously coloured birds—Novelty appreciated—Summary
of the four chapters on Birds.
We must now consider the transmission of characters,
as limited by age, in reference to sexual
selection. The truth and importance of the principle
of inheritance at corresponding ages need
not here be discussed, as enough has already
been said on the subject. Before giving the several
rather complex rules or classes of cases, under
which the differences in plumage between
the young and the old, as far as known to me,
may be included, it will be well to make a few
preliminary remarks.
With animals of all kinds when the adults differ
in colour from the young, and the colours of the
latter are not, as far as we can see, of any special
service, they may generally be attributed,
like various embryological structures, to the
retention of a former character. But this view