It is, no doubt, extremely difficult even to conjecture by what gradations many structures have been perfected, more especially amongst broken and failing groups of organic
beings; beings; 1859 1860 | beings, 1861 1866 1869 1872 |
but but 1859 1860 |
which have suffered much extinction; but 1861 1866 1869 1872 |
we see so many strange gradations in nature,
as is proclaimed by the canon, "Natura non facit saltum," as is proclaimed by the canon, "Natura non facit saltum," 1859 |
OMIT 1860 1861 1866 1869 1872 |
that we ought to be extremely cautious in saying that any organ or instinct, or
any any 1859 1860 1861 1866 1872 | the 1869 |
whole
being, being, 1859 1860 1861 1866 | structure, 1869 1872 |
could not have arrived at its present state by many graduated steps. There are, it must be admitted, cases of special difficulty
on on 1859 1860 1861 1866 | opposed to 1869 1872 |
the theory of natural selection; and one of the most curious of these is the existence
of of 1859 1860 1861 1866 1869 |
in the same community of 1872 |
two or three defined castes of workers or sterile
females females 1859 1860 1861 1866 | female 1869 1872 |
in the same community of ants; in the same community of ants; 1859 1860 1861 1866 |
ants in the same community; 1869 |
ants; 1872 |
but I have attempted to show how
this this 1859 1860 | these 1861 1866 1869 1872 |
difficulty difficulty 1859 1860 | difficulties 1861 1866 1869 1872 |
can be mastered. |
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With respect to the almost universal sterility of species when first crossed, which forms so remarkable a contrast with the almost universal fertility of varieties when crossed, I must refer the reader to the recapitulation of the facts given at the end of the
eighth eighth 1859 1860 1861 1866 1869 | ninth 1872 |
chapter, which seem to me conclusively to show that this sterility is no more a special endowment than is the incapacity of two
trees trees 1859 1860 1861 |
distinct trees 1866 1869 |
distinct kinds of trees 1872 |
to be grafted
together, together, 1859 | together; 1860 1861 1866 1869 1872 |
but that it is incidental on
constitutional constitutional 1859 1860 1861 | constitutional 1866 1869 1872 |
differences
in in 1859 1860 1861 | confined to 1866 1869 1872 |
the reproductive systems of the intercrossed species. We see the truth of this conclusion in the vast difference in the
result, result, 1859 1860 1861 1866 | results 1869 1872 |
when when 1859 1860 1861 1866 | of crossing 1869 1872 |
the same two species
are crossed reciprocally; are crossed reciprocally; 1859 1860 1861 |
are crossed reciprocally,— 1866 |
reciprocally,— 1869 1872 |
that is, when one species is first used as the father and then as the
mother. mother. 1859 1860 1861 1872 | mother: 1866 1869 |
↑1 blocks not present in 1859 1860 1861; present in 1866 1869 1872 | Analogy
from the consideration of dimorphic and trimorphic plants clearly leads to
the same conclusion, for when the forms are illegitimately united, they yield few or no seed, and their offspring are more or less sterile; and these forms belong to
the same undoubted species,
and
differ from each other in no respect
except in their reproductive organs and functions.
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The The 1859 1860 | Although the 1861 1866 1869 1872 |
fertility of varieties when intercrossed and of their mongrel offspring
cannot cannot 1859 1860 |
has been asserted by so many authors to be universal, this cannot 1861 1866 1869 1872 |
be considered
as universal; nor is their very general fertility surprising when we remember that it is not likely that either their constitutions or their reproductive systems should have been profoundly modified. as universal; nor is their very general fertility surprising when we remember that it is not likely that either their constitutions or their reproductive systems should have been profoundly modified. 1859 1860 |
correct after the facts given on the authority of Gärtner and Kölreuter. 1861 1866 1869 |
as quite correct after the facts given on the high authority of Gärtner and Kölreuter. 1872 |
Moreover, most of the varieties which Moreover, most of the varieties which 1859 1860 1866 1869 |
Nor is the very general fertility of varieties, when crossed, surprising, when we remember that it is not likely that either their constitutions or their reproductive systems should 1861 |
Most of the varieties which 1872 |
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