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South 1859 1860 1861
tropical and temperate South 1866 1869 1872

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

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

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 intervals of time, is widely different in different groups. The extinction of species and of whole groups of species, which has played so conspicuous a part in the history of the organic world, almost inevitably follows
from
on
the principle of natural selection; for old forms
are
will be
supplanted by new and improved forms. Neither single species nor groups of species
re-appear
reappear
when the chain of ordinary generation
is
has
once
been
been
broken. The gradual diffusion of dominant
forms
forms,
with the slow modification of their descendants, causes the forms of life, after long intervals of time, to appear as if they had changed simultaneously throughout the world. The fact of the fossil remains of each formation being in some degree intermediate in character between the