The Descent of Man

statement is too strong.) Calling to my recollection
the desert-birds of South America, as well
as most of the ground-birds of Great Britain, it
appeared to me that both sexes in such cases
are generally coloured nearly alike. Accordingly,
I applied to Mr. Tristram with respect to
the birds of the Sahara, and he has kindly given
me the following information. There are twenty-six
species belonging to fifteen genera,
which manifestly have their plumage coloured
in a protective manner; and this colouring is all
the more striking, as with most of these birds it
differs from that of their congeners. Both sexes
of thirteen out of the twenty-six species are
coloured in the same manner; but these belong
to genera in which this rule commonly prevails,
so that they tell us nothing about the protective
colours being the same in both sexes of desertbirds.
Of the other thirteen species, three belong
to genera in which the sexes usually differ
from each other, yet here they have the sexes
alike. In the remaining ten species, the male