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and
and
therefore these same characters would be more likely
again
still
to
vary
be variable
than the generic characters which have been inherited without change for an
immense
enormous
period. It is inexplicable on the theory of creation why a part developed in a very unusual manner in
any
any
one species
alone of
of
a genus, and therefore, as we may naturally infer, of great importance to
that
the
species, should be eminently liable to variation; but, on
our
my
view, this part has
undergone
undergone,
since the several species branched off from a common progenitor, an unusual amount of variability and modification, and therefore we might expect
the
this
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.
Glancing at instincts, marvellous as some are, they offer no greater difficulty than
do
does
corporeal
structures
structure
on the theory of the natural selection of successive, slight, but profitable modifications. We can thus understand why nature moves by graduated steps in endowing different animals of the same class with their several instincts. I have attempted to show how much light the principle of
graduation
gradation
throws on the admirable architectural powers of the hive-bee. Habit no doubt
often
sometimes
comes into play in modifying instincts; but it certainly is not indispensable, as we
see
see,
in the case of neuter insects, which leave no progeny to inherit the effects of long-continued habit. On the view of all the species of the same genus having descended from a common parent, and having inherited much in common, we can understand how it is that allied species, when placed under
widely
considerably
different conditions of life,