The Descent of Man

I. When the adult male is more beautiful or
conspicuous than the adult female, the young
of both sexes in their first plumage closely resemble
the adult female, as with the common
fowl and peacock; or, as occasionally occurs,
they resemble her much more closely than they
do the adult male.
II. When the adult female is more conspicuous
than the adult male, as sometimes though rarely
occurs, the young of both sexes in their first
plumage resemble the adult male.
III. When the adult male resembles the adult
female, the young of both sexes have a peculiar
first plumage of their own, as with the robin.
IV. When the adult male resembles the adult
female, the young of both sexes in their first
plumage resemble the adults, as with the kingfisher,
many parrots, crows, hedge-warblers.