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See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1869
1872

↑ 2 blocks not present in 1859 1860 1861 1866; present in 1869 1872
Or take the case of two species which in their present state when crossed, produce few and sterile offspring; now, what is there which could favour the survival of those individuals which happened to be endowed in a slightly higher degree with mutual infertility, and which thus approached by one small step towards absolute sterility? Yet an advance of this kind, if the theory of natural selection be brought to bear, must have incessantly occurred with many species, for a multitude are mutually quite barren.
→ have 1866
and fertility have 1869 1872
→ if 1866
not belonging to a social community, if 1869 1872
→ to its nearest relatives or to any 1866
or indirectly give any advantage to the 1869 1872
↑ 3 blocks not present in 1859 1860 1861 1866 1869; present in 1872
But it would be superfluous to discuss this question in detail; for with plants we have conclusive evidence that the sterility of crossed species must be due to some principle, quite independent of natural selection. Both Gärtner and Kölreuter have proved that in genera including numerous species, a series can be formed from species which when crossed yield fewer and fewer seeds, to species which never produce a single seed, but yet are affected by the pollen of certain other species, for the germen swells. It is here manifestly impossible to select the more sterile individuals, which have already ceased to yield seeds; so that this acme of sterility, when the germen alone is affected, cannot have been gained through selection; and from the laws governing the various grades of sterility being so uniform throughout the animal and vegetable kingdoms, we may infer that the cause, whatever it may be, is the same or nearly the same in all cases.
→ same or of other varieties to the 1866
OMIT 1869
→ any one 1866
a variety, when deposited on the stigma of the same 1869
→ so that, when deposited by any means on the stigmas of the flowers of 1866
this would certainly be an advantage to the variety; for 1869
→ variety, it 1866
pollen would thus 1869
→ this would certainly be an advantage to the variety; for it would thus escape being bastardised and deteriorated in 1866
and prevent deterioration of 1869
to that high degree which is common with so many species, and which is universal with species which have been differentiated to a generic or family rank, will find the subject extraordinarily complex. After mature reflection it seems to me that this could not have been effected through natural
selection.
selection;
for
for
it
it
could
could
not
not
not
have
have
been
been
of
of
no
any
any
direct
direct
advantage
advantage
to
to
an
an
individual
individual
animal
animal
to
to
breed
breed
badly
poorly
poorly
with
with
another
another
individual
individual
of
of
a
a
different
different
variety,
variety,
and
and
thus
thus
to
to
leave
leave
few
few
offspring;
offspring;
consequently
consequently
such
such
individuals
individuals
could
could
not
not
have
have
been
been
preserved
preserved
or
or
selected.
selected.
↑ With sterile neuter insects we have reason to believe that modifications in their structure →have been slowly accumulated by natural selection, from an advantage having been thus indirectly given to the community to which they belonged over other communities of the same species; but an individual
animal
animal,
→if rendered slightly sterile when crossed with some other variety, would not thus
itself gain
indirectly give
any advantage →to its nearest relatives or to any other individuals of the same variety, thus leading to their preservation. From these considerations I infer, as far as animals are concerned, that the various degrees of lessened fertility which occur with species when crossed cannot have been slowly accumulated by means of natural selection. ↑
With plants, it is possible that the case may be
some-what different.
different.
With
very
very
many kinds, insects constantly
carry
bring
pollen from neighbouring plants
to
of
the →same or of other varieties to the
stigmas
stigma
of each flower; and with some
species this
this
is effected by the wind.
Now
Now,
if the pollen of →any one
variety,
variety
should become by spontaneous variation in ever so slight a degree prepotent over the pollen of other varieties, →so that, when deposited by any means on the stigmas of the flowers of its own →variety, it
obliterate
obliterated
the effects of
the
previously placed
pollen of other varieties, →this would certainly be an advantage to the variety; for it would thus escape being bastardised and deteriorated in