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1859
1860
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1869
1872

Compare with:
1859
1861
1866
1869
1872

but 1859 1860
or on the gradual acclimatisation of new species to the various climates through which they must pass, but 1861
or on the gradual acclimatisation of new species to the various climates through which they have to pass, but 1866
and on the gradual acclimatisation of new species to the various climates through which they might have to pass, but 1869 1872

long run 1859 1860 1861
course of time 1866 1869 1872

spreading. 1859 1860 1861 1866
spreading and would ultimately prevail. 1869 1872

sea. 1859 1860 1861 1866
land than with those of the sea. 1869 1872

new 1859 1860 1861
any one new 1866

varying, and far-spreading species, which
have already
already have
invaded to a certain extent the territories of other species, should be those which would have the best chance of spreading still further, and of giving rise in new countries to
other new
new
varieties and species. The process of diffusion
would
may
often be very slow,
being
being
depending
dependent
on climatal and geographical changes,
or
or
on strange accidents, but in the long run the dominant forms
would
will
generally succeed in spreading. The diffusion would, it is probable, be slower with the terrestrial inhabitants of distinct continents than with the marine inhabitants of the continuous sea. We might therefore expect to find, as we
apparently
apparently
do find, a less strict degree of
parallelism
parallel
succession
succession
in the
succession
productions
of the
productions
land than
of the sea.
Dominant species spreading from any region might encounter still more dominant species, and then their triumphant course, or even their existence, would cease. We know not at all precisely what are all the conditions most favourable for the multiplication of new and dominant species; but we can, I think, clearly see that a number of individuals, from giving a better chance of the appearance of favourable variations, and that severe competition with many already existing forms, would be highly favourable, as would be the power of spreading into new territories. A certain amount of isolation, recurring at long intervals of time, would probably be also favourable, as before explained. One quarter of the world may have been most favourable for the production of new and dominant species on the land, and another for those in the waters of the sea. If two great regions had been for a long period favourably circumstanced in an equal degree, whenever their inhabitants met, the battle would be prolonged and severe; and some from one birthplace and some from the other might be victorious. But in the course of time, the