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1859
1860
1861
1866
1869
1872

Compare with:
1860
1861
1866
1869
1872

conditions 1859
physical conditions at least 1860
physical conditions 1861 1866

most affect those animals 1859 1860 1861 1866
affect those animals most 1869
chiefly affect those animals 1872

so that whatever intercrossing took place would be chiefly between 1859 1860 1861 1866
and afterwards spread, so that the crossing would be chiefly between 1869
and afterwards spread, so that 1872

same new variety. 1859 1860 1861 1866
new variety living together in the same place. 1869
new variety would chiefly cross together. 1872

same variety, as the 1859 1860 1861 1866
OMIT 1869 1872

with other varieties 1859 1860 1861 1866
OMIT 1869 1872

in the case of slow-breeding 1859 1860 1861 1866
in the case of 1869
with 1872

unite 1859 1860 1861 1866 1872
breed slowly and unite 1869

we 1859 1860 1861 1866 1869
and which do not propagate rapidly, we 1872

overrate 1859 1860 1861 1866
assume that 1869
assume that free intercrossing would always eliminate 1872

intercrosses in retarding 1859 1860 1861 1866
OMIT 1869 1872

for 1859 1860 1861 1866 1872
will always be immediately overpowered by free intercrossing; for 1869

a considerable catalogue 1859 1860 1861 1866
a considerable body 1869
forward a considerable body 1872

varieties of the same kind 1859 1860 1861 1866 1869
the individuals of each variety 1872

counterbalanced
terbalanced
by natural selection always tending to modify all the individuals in each district in exactly the same manner to the conditions of each; for in a continuous area, the conditions will generally graduate away insensibly from one district to another.
The
The
Intercrossing
intercrossing
will most affect those animals which unite for each
birth
birth,
and
which
wander much, and which do not breed at a very quick rate. Hence
with
in
animals of this nature, for
instance,
instance
in
in
birds, varieties will generally be confined to separated countries; and this I
find
believe
to be the case.
With
In
hermaphrodite organisms which cross only occasionally, and likewise
with
in
animals which unite for each birth, but which wander little and
which
which
can increase at a
very
very
rapid rate, a new and improved variety might be quickly formed on any one spot, and might there maintain itself in a
body
body,
so that whatever intercrossing took place would be chiefly between the individuals of the same new variety. A local variety when once thus formed might subsequently slowly spread to other districts. On
this
the above
principle, nurserymen always prefer
saving
getting
seed from a large body of
plants,
plants
as
of
the same variety, as the chance of intercrossing with other varieties is thus lessened.
Even in the case of slow-breeding
animals
animals,
which unite for each birth, we must not overrate the effects of intercrosses in retarding natural
selection
selection;
for I can bring a considerable catalogue of
facts
facts,
showing that within the same area,
two varieties
varieties
of the same animal
may
can
long remain distinct, from haunting different stations, from breeding at slightly different seasons, or from varieties of the same kind preferring to pair together.
Intercrossing plays a very important part in nature
by
in
keeping the individuals of the same species, or of the same variety, true and uniform in character. It will obviously thus act far more efficiently with those animals