The principle included in these remarks may be extended. It is
notorious that specific characters are more variable than generic. To
explain by a simple example what is meant. If some species in a large
genus of plants had blue flowers and some had red, the colour would be
only a specific character, and no one would be surprised at one of the
blue species varying into red, or conversely; but if all the species
had blue flowers, the colour would become a generic character, and its
variation would be a more unusual circumstance. I have chosen this
example because an explanation is not in this case applicable, which
most naturalists would advance, namely, that specific characters are
more variable than generic, because they are taken from parts of less
physiological importance than those commonly used for classing genera.
I believe this explanation is partly, yet only indirectly, true; I
shall, however, have to return to this subject in our chapter on
Classification. It would be almost superfluous to adduce evidence in
support of the above statement, that specific characters are more
variable than generic; but I have repeatedly noticed in works on
natural history, that when an author has remarked with surprise that
some IMPORTANT organ or part, which is generally very constant
throughout large groups of species, has DIFFERED considerably in
closely-allied species, that it has, also, been VARIABLE in the
individuals of some of the species.
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