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those which do not change will 1859 1860 1861 1866
otherwise they would 1869 1872

long-enduring fossiliferous formations 1859 1860 1861 1866
long-enduring formations, 1869
enduring formations, rich in fossils, 1872

depends 1859 1860 1861 1866 1872
rich in fossils, depends 1869

areas whilst subsiding, 1859 1860 1861 1866
subsiding areas, 1869 1872

consequently 1859 1860 1861
of time; consequently 1866 1869 1872

progenitors. 1859 1860 1861 1866
progenitors, and organisms already differing would vary in a different manner. 1869
progenitors; and organisms already differing would vary in a different manner. 1872

our fantail-pigeons were all 1859 1860 1861 1866
all our fantail pigeons were 1869 1872

by striving during long ages for the same object, 1859 1860 1861 1866
OMIT 1869 1872

would
will
be liable to
be
be
extermination.
exterminated.
Hence we
can
can
see why all the species in the same region do at last, if we look to
long
wide
enough intervals of time, become
modified,
modified;
for those which do not change will become extinct.
In members of the same class the average amount of change, during long and equal periods of time, may, perhaps, be nearly the same; but as the accumulation of long-enduring fossiliferous formations depends on great masses of sediment
being
having been
deposited on areas whilst subsiding, our formations have been almost necessarily accumulated at wide and irregularly intermittent
intervals
intervals;
consequently the amount of organic change exhibited by the fossils embedded in consecutive formations is not equal. Each formation, on this view, does not mark a new and complete act of creation, but only an occasional scene, taken almost at hazard, in
an ever
a
slowly changing drama.
We can clearly understand why a species when once lost should never reappear, even if the very same conditions of life, organic and inorganic, should recur. For though the offspring of one species might be adapted (and no doubt this has occurred in innumerable instances) to fill the
exact
exact
place of another species in the economy of nature, and thus supplant it; yet the two forms— the old and the new— would not be identically the same; for both would almost certainly inherit different characters from their distinct progenitors. For instance, it is
just
just
possible, if our fantail-pigeons were all destroyed, that
fanciers
fanciers,
by striving during long ages for the same object, might make a new breed hardly distinguishable from
the
our
present
breed;
fantail;
but if the parent rock-pigeon were
likewise
also
destroyed, and
under
in
nature we have every reason to believe that
the
the
parent-forms
parent-form
are
will
generally
be
be
supplanted and exterminated by
their
its
improved offspring, it is
quite
quite
incredible
in- credible