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by checking immigration and consequently competition, 1859 1860 1861 1866
OMIT 1869 1872

and 1859 1860 1861 1866 1869
at a slow rate; and 1872

importance in the production of new species. 1859 1860 1861 1866 1869
much importance. 1872

individuals supported on it will necessarily be very 1859 1860 1861 1866
inhabitants will be 1869 1872

fewness of individuals will greatly 1859 1860 1861 1866
this will 1869 1872

the appearance of 1859 1860 1861 1866 1869
OMIT 1872

4 blocks not present in 1859 1860; present in 1861 1866 1869 1872
The mere lapse of time by itself does nothing either for or against natural selection. I state this because it has been erroneously asserted that the element of time is assumed by me to play an all-important part in natural selection, as if all species were necessarily undergoing slow modification from some innate law. Lapse of time is only so far highly important, as it gives a better chance of beneficial variations arising, being selected, accumulated, and fixed, in relation to the slowly changing organic and inorganic conditions of life. It likewise favours the direct action of new or changed physical conditions of life.

species inhabiting it, will be found to be 1859 1860 1861
species inhabiting it will be found to be 1866
different species inhabiting it is 1869
species inhabiting it is 1872

else. 1859 1860 1861 1866
else in the world. 1869 1872

I do not doubt that 1859 1860
OMIT 1861 1866 1869 1872

in their structure and constitution. Lastly,
isolation
isolation,
by checking immigration and consequently competition, will give time for
a
any
new variety to be
slowly
slowly
improved
improved;
and this may sometimes be of importance in the production of new species. If, however, an isolated area be very small, either from being surrounded by barriers, or from having very peculiar physical conditions, the total number of the individuals supported on it will necessarily be very small; and fewness of individuals will greatly retard the production of new species through natural selection, by decreasing the
chances
chance
of the appearance of favourable
individual differences.
variations arising.
variations.
If we turn to nature to test the truth of these remarks, and look at any small isolated area, such as an oceanic island, although the
total
total
number of
the
the
species inhabiting it, will be found to be small, as we shall see in our chapter on
Geographical
geographical
Distribution;
distribution;
yet of
the
these
species a very large proportion are endemic,— that is, have been produced there, and nowhere else. Hence an oceanic island at first sight seems to have been highly favourable for the production of new species. But we may thus
greatly
greatly
deceive ourselves, for to ascertain whether a small isolated area, or a large open area like a continent, has been most favourable for the production of new organic forms, we ought to make the comparison within equal times; and this we are incapable of doing.
Although I do not doubt that isolation is of
great
considerable
importance in the production of new species, on the whole I am inclined to believe that largeness of area is
still
of
more
important,
importance,
more
more
especially
for
in
the production of
species
species,
which
shall
will
prove capable of enduring for a long period, and of spreading widely. Throughout a great and open area, not only will there be a better chance of favourable
variations,
variations
arising from the large number of individuals of the same species