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1859
1860
1861
1866
1869
1872

Compare with:
1859
1861
1866
1869
1872

be 1859 1860
have been 1861 1866 1869
have been very 1872

Its action depends on there being 1859 1860 1861 1866
The result depends on there being 1869
It can act only when there are 1872

polity of nature, 1859 1860 1861 1866 1869
natural polity of a district 1872

some of the inhabitants of the country undergoing 1859 1860 1861
some of the inhabitants of the country under- going 1866
some of the inhabitants of the country under-going 1869
the 1872

kind. 1859 1860 1861 1866 1869
of its existing inhabitants. 1872

1 blocks not present in 1859 1860 1861 1866 1872; present in 1869
But the effects of natural selection will probably still oftener depend on some few of the inhabitants becoming slowly modified; the mutual relations of the other inhabitants being thus disturbed.

On the other hand, 1859 1860 1861 1866
But 1869 1872

often only at 1859 1860 1861
generally at only 1866
in effecting changes, at 1869
only at 1872

prevented,
vented,
so that new places in the polity of each island will have
had to
to
be filled up by
the modification
modifications
of the old inhabitants; and time will
have been
be
allowed for the varieties in each to become well modified and perfected. When, by renewed elevation, the islands
were
shall be
reconverted
re-converted
into a continental area, there will again be severe competition: the most favoured or improved varieties will
have been
be
enabled to spread: there will
have been
be
much extinction of the less improved forms, and the relative proportional numbers of the various inhabitants of the
reunited
renewed
continent will again
have been
be
changed; and again there will
have been
be
a fair field for natural selection to improve still further the inhabitants, and thus
to produce
produce
new species.
That natural selection
always
generally
will always
will always
acts
act
with extreme
slowness
slowness,
I fully admit. Its action depends on there being places in the polity of nature, which can be better
filled through
occupied by
some of the inhabitants of the country undergoing
modifications
modification
of some kind. The existence of such places will often depend on physical changes, which are generally very slow, and on the immigration of better adapted forms
being
having been
checked. But the action of natural selection will probably still oftener depend on some
few of
of
the inhabitants becoming slowly modified; the mutual relations of many of the other inhabitants being thus disturbed. Nothing can be effected, unless favourable variations occur, and variation itself is apparently always a
very
very
slow process. The process will often be greatly retarded by free intercrossing. Many will exclaim that these several causes are amply sufficient
wholly
wholly
to
neutralise
stop
the
power
action
of natural selection. I do not believe so. On the other hand, I do believe that natural selection
will always
generally
will generally
always
act
acts
very
slowly
slowly,
often only at long intervals of time, and
only
generally
on
only
only
a
very
very
few of the inhabitants of the same
region.
region
at
at
the
the
same
same
time.
time.
I further
believe
believe,
that
this
these
this very
slow,
inter- mittent
intermittent
intermit- tent