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1859
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1866
1869
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1859
1860
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1869
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the changed conditions of 1859 1860 1861 1866
OMIT 1869 1872

there are at least 1859 1860 1861 1866
species present 1869 1872

have admitted the existence of varieties, which they have considered 1861 1866
have admitted the existence of varieties, which they think 1859 1860
admit that varieties exist, which are considered 1869
admit that natural varieties exist, which are considered 1872

1 blocks not present in 1859 1860 1861; present in 1866 1869 1872
On separate continents, and on different parts of the same continent when divided by barriers of any kind, and on outlying islands, what a multitude of forms exist, which some experienced naturalists rank as varieties, others as geographical races or sub-species, and others as distinct, though closely allied species!

we have variability as well as a powerful agent always ready to act, 1861
we have under nature variability and a powerful agent always ready to act and select, 1859 1860
animals and plants do vary, let it be ever so slowly or so little, 1866
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 beings, under their excessively complex relations of life, would 1859 1860 1861
useful to them under their extremely complex relations of life would 1866
beneficial would 1869
beneficial, 1872

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

himself, should nature fail in selecting variations useful, 1859 1860 1861
himself, should nature fail in preserving or selecting variations useful, 1866
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

nature, in the same way as they
generally
generally
have varied under the changed conditions of domestication. And if there
has been
be
any variability under nature, it would be an unaccountable fact if natural selection
did
had
not come into play. It has often been asserted, but the assertion is
quite
quite
incapable of proof, that the amount of variation under nature is a strictly limited quantity. Man, though acting on external characters alone and often capriciously, can produce within a short period a great result by adding up mere individual differences in his domestic productions; and every one admits that there are at least individual
differences.
differences
in
in
species
species
under
under
nature.
nature.
But, besides such differences, all naturalists have admitted the existence of varieties, which they have considered sufficiently distinct to be worthy of record in
systematic
their systematic
works. No one
has
can
drawn
draw
any clear distinction between individual differences and slight varieties; or between more plainly marked varieties and sub-species, and species. Let it be observed how naturalists differ in the rank which they assign to the many representative forms in Europe and North America.
If
then,
then
we have variability as well as a powerful agent always ready to act, why should we doubt that variations in
some
any
way useful to beings, under their excessively complex relations of life, would be preserved, accumulated, and inherited?
If
Why, if
man can by patience select variations
most
most
useful to himself, should nature fail in 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