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1859
1860
1861
1866
1869
1872

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1859
1860
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1869
1872

the several islands in the same archipelago, 1866
outlying islands, 1869 1872

1 blocks not present in 1866 1869 1872; present in 1859 1860 1861
Let it be observed how naturalists differ in the rank which they assign to the many representative forms in Europe and North America.

animals and plants do vary, let it be ever so slowly or so little, 1866
we have under nature variability and a powerful agent always ready to act and select, 1859 1860
we have variability as well as a powerful agent always ready to act, 1861
animals and plants do vary, let it be ever so little or so slowly, 1869
animals and plants do vary, let it be ever so slightly or slowly, 1872

we doubt that variations 1859 1860 1861 1866
we doubt that the variations or individual differences, which are 1869
not variations or individual differences, which are 1872

useful to them under their extremely complex relations of life would 1866
useful to beings, under their excessively complex relations of life, would 1859 1860 1861
beneficial would 1869
beneficial, 1872

occasionally occur, and then be preserved and accumulated by natural selection? 1866
be preserved, accumulated, and inherited? 1859 1860 1861
be preserved and accumulated through natural selection, or the survival of the fittest? 1869 1872

himself, should nature fail in preserving or selecting variations useful, 1866
himself, should nature fail in selecting variations useful, 1859 1860 1861
him, why, 1869 1872

conditions 1859 1860 1861 1866
and complex conditions 1869 1872

to her 1859 1860 1861 1866
should not variations useful to natures 1869
should not variations useful to nature's 1872

products? 1859 1860 1861 1866
products often arise, and be preserved or selected? 1869 1872

itself 1859 1860 1861 1866 1869
the highest degree 1872

divided by barriers of any kind, and on the several islands in the same archipelago, what a
multitude
host
of forms exist, which some experienced naturalists rank as
varieties,
mere varieties,
others as geographical races or sub-species, and others as distinct, though closely allied species!
If
then,
then
animals and plants do vary, let it be ever so slowly or so little, why should we doubt that variations in
any
some
way useful to them under their extremely complex relations of life would occasionally occur, and then be preserved and accumulated by natural selection?
If
Why, if
man can by patience select variations
most
most
useful to himself, should nature fail in preserving or selecting variations useful, under changing conditions of life, to her living products? What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature,— favouring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life. The theory of natural selection, even if we
look
looked
no
further
farther
than this, seems to
me to
me to
be in itself probable. I have already recapitulated, as fairly as I could, the opposed difficulties and objections: now let us turn to the special facts and arguments in favour of the theory.
On the view that species are only strongly marked and permanent varieties, and that each species first existed as a variety, we can see why it is that no line of demarcation can be drawn between species, commonly supposed to have been produced by special acts of creation, and varieties which are acknowledged to have been produced by secondary laws. On this same view we can understand how it is that in
a
each
region where many species of a genus have been produced, and where they now flourish, these same species should