The Descent of Man

denly, are often, as I have elsewhere shewn (42.
'Variation of Animals and Plants under Domestication,'
vol. ii. p. 92.), transmitted either unaltered
or not at all. We thus see that two distinct
forms of the same species may co-exist in the
same district, and we cannot doubt that if the
one had possessed any advantage over the other,
it would soon have been multiplied to the
exclusion of the latter. If, for instance, the male
pied ravens, instead of being persecuted by
their comrades, had been highly attractive (like
the above pied peacock) to the black female
ravens their numbers would have rapidly increased.
And this would have been a case of
sexual selection.
With respect to the slight individual differences
which are common, in a greater or less degree,
to all the members of the same species, we have
every reason to believe that they are by far the
most important for the work of selection. Secondary
sexual characters are eminently liable