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On the ordinary view of each species having been independently created, why should
specific
or those by which the species of the same genus differ from each other, be more variable than
generic characters in which they all agree? Why, for instance, should the colour of a flower be more likely to vary in any one species of a genus, if the other
→supposed to have been created independently, have
differently coloured flowers, than if all
→the species of the genus have
the same coloured flowers? If species are only well-marked varieties, of which the characters have become in a high degree permanent, we can understand this fact; for they have already varied since they branched off from a common progenitor in certain characters, by which they have come to be specifically distinct from each other;
therefore these same characters would be more likely
to
than the generic characters which have been inherited without change for an
period. It is inexplicable on the theory of creation why a part developed in a very unusual manner in
one species
a genus, and therefore, as we may naturally infer, of great importance to
species, should be eminently liable to variation; but, on
view, this part has
since the several species branched off from a common progenitor, an unusual amount of variability and modification, and therefore we might expect
part generally to be still variable. But a part may be developed in the most unusual manner, like the wing of a bat, and yet not be more variable than any other structure, if the part be common to many subordinate forms, that is, if it has been inherited for a very long period; for in this case it will have been rendered constant by long-continued natural selection. |
