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1859
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1869
1872

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1860
1861
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1869
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feel little curiosity, 1859 1860 1861 1866
be dull, 1869 1872

on my theory, 1859 1860 1861 1866
OMIT 1869 1872

or, 1859 1860 1861 1866
each other, or, 1869 1872

like each other. 1859 1860 1861 1866
alike. 1869 1872

natural 1859 1860 1861 1866 1869
variation and natural 1872

in a quite 1859 1860 1861 1866
in a 1869
probably in a 1872

and reaction, in their mutual struggles for life;— 1859 1860 1861 1866
of the inhabitants on each other in leading to the preservation of different modifications; 1869 1872

being, 1859 1860 1861 1866
in the struggle for life being, 1869 1872

the American continent and in the American seas. We see in these facts some deep organic bond,
prevailing
prevailing
throughout space and time, over the same areas of land and water,
and
and
independently
independent
of
their
their
physical conditions. The naturalist must feel little curiosity, who is not led to inquire what this bond is.
The
This
bond
bond,
on my theory, is simply inheritance, that cause which alone, as far as we positively know, produces organisms quite
like
like,
or, as we see in the case of
varieties,
varieties
nearly like each other. The dissimilarity of the inhabitants of different regions may be attributed to modification through natural selection, and in a quite subordinate degree to the
definite
direct
influence of different physical conditions. The
degrees
degree
of dissimilarity will depend on the migration of the more dominant forms of life from one region into another having been
prevented
effected with
effected with
more or less
effectually,
effectually prevented,
ease,
at periods more or less remote;— on the nature and number of the former
immigrants; —
immigrants;—
and on
the
their
action and reaction, in their mutual struggles for life;— the relation of organism to organism being, as I have already often remarked, the most important of all relations. Thus the high importance of barriers comes into play by checking migration; as does time for the slow process of modification through natural selection. Widely-ranging species, abounding in individuals, which have already triumphed over many competitors in their own widely-extended
homes,
homes
will have the best chance of seizing on new places, when they spread into new countries. In their new homes they will be exposed to new conditions, and will frequently undergo further modification and improvement; and thus they will become still further victorious, and will produce groups of modified descendants. On this principle of inheritance with modification, we can understand how it is that sections of genera, whole genera,