The Descent of Man

valuable, as Mr. Riley here discusses all the
objections which have been raised against Mr.
Bates's theory.)
As some writers have felt much difficulty in
understanding how the first steps in the process
of mimicry could have been effected
through natural selection, it may be well to
remark that the process probably commenced
long ago between forms not widely dissimilar
in colour. In this case even a slight variation
would be beneficial, if it rendered the one species
more like the other; and afterwards the
imitated species might be modified to an extreme
degree through sexual selection or other
means, and if the changes were gradual, the
imitators might easily be led along the same
track, until they differed to an equally extreme
degree from their original condition; and they
would thus ultimately assume an appearance
or colouring wholly unlike that of the other
members of the group to which they belonged.