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South 1859 1860 1861
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On the other hand, these 1859 1860 1861 1866
This similarity 1869 1872

gives 1861
gives, 1859 1860
does give, strongly 1866 1869 1872

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, yet
should
should
follow nearly the same instincts; why the
thrushes
thrush
of South America, for instance,
line
lines
their
her
nests
nest
with mud like our British species. On the view of instincts having been slowly acquired through natural
selection,
selection
we need not marvel at some instincts being
apparently
apparently
not perfect and liable to mistakes, and at many instincts causing other animals to suffer.
If species be only well-marked and permanent varieties, we can at once see why their crossed offspring should follow the same complex laws in their degrees and kinds of resemblance to their parents,— in being absorbed into each other by successive crosses, and in other such points,— as do the crossed offspring of acknowledged varieties. On the other hand, these would be
a strange
strange
fact,
facts
if species
had
have
been independently
created
created,
and varieties
had
have
been produced
through
by
secondary laws.
If we admit that the geological record is imperfect
to
in
an extreme degree, then
the
such
facts,
facts
which
as
the record gives support the theory of descent with modification. New species have come on the stage slowly and at successive intervals; and the amount of change, after equal