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1859
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allied species, 1859 1860 1861 1866
the several species belong- ing to the same genus, 1869
the several species belonging to the same genus, 1872

(generally of the more dominant forms of life), 1859 1860 1861 1866
OMIT 1869 1872

which separate our 1859 1860 1861 1866
in not only separating, but in apparently forming the 1869 1872

sub-genera, genera, and families; 1859 1860 1861 1866
related species within the same areas; 1869 1872

in 1859 1860 1861 1866
linked together in 1869 1872

linked together by affinity, 1859 1860 1861
linked together, 1866
OMIT 1869 1872

region; according to the nature of the 1859 1860 1861
of the regions, or both; according to the nature of the 1866 1869 1872

different 1859 1860 1861 1866
the two or more 1869 1872

as we do find, 1859 1860 1861 1866 1869
OMIT 1872

If the difficulties be not insuperable in admitting that in the long course of time
all the
the
individuals of the same species, and likewise of allied species, have proceeded from some one source; then
I think
I think
all the grand leading facts of geographical distribution are explicable on the theory of
migration,
migration
(generally of the more dominant forms of life), together with subsequent modification and the multiplication of new forms. We can thus understand the high importance of barriers, whether of land or water, which separate our several zoological and botanical provinces. We can thus understand the
concentration
localisation
of sub-genera, genera, and families; and how it is that under different latitudes, for instance in South America, the inhabitants of the plains and mountains, of the forests, marshes, and deserts, are in so mysterious a
manner,
manner
linked together by affinity, and are likewise linked to the extinct beings which formerly inhabited the same continent. Bearing in mind that the mutual
relations
relation
of organism to organism
are
is
of the highest importance, we can see why two areas having nearly the same physical conditions should often be inhabited by very different forms of life; for according to the length of time which has elapsed since
new colonists
the colonists
new inhabitants
entered one region; according to the nature of the communication which allowed certain forms and not others to enter, either in greater or lesser numbers; according or not, as those which entered happened to come
into
in
more or less direct competition with each other and with the
aborigines:
aborigines;
and according as the immigrants were capable of varying more or less rapidly, there would ensue in different regions, independently of their physical conditions, infinitely diversified conditions of life,— there would be an almost endless amount of organic action and reaction,— and we should
find
find,
as we do find, some groups of beings greatly, and some only slightly
modified;—
modified,—
some
developed
deve- loped