Darwin Online
Publications
Manuscripts
Biography
Media
About Us
Advanced search

See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1859
1860
1861
1866
1869

→ for the production of new forms through Natural Selection. 1872
to Natural Selection .— 1859
to Natural Selection. — 1860 1861
to Natural Selection. 1866
for the production of new forms through Natural Selection. 1869
→ variability, under which term 1869 1872
inheritable and diversified variability is favourable, but I believe mere 1859 1860
variability will evidently be favourable for the work of natural selection, but mere 1861 1866
→ are always included, will evidently be favourable. 1869 1872
suffice for the work. 1859 1860
probably suffice. 1861 1866
→ within any given period for the appearance of profitable variations, 1872
for the appearance within any given period of profitable variations, 1859 1860 1861 1866
for the appearance of profitable variations within any given period, 1869
→ OMIT 1861 1866 1869 1872
it may be said, 1859 1860
→ selection. The tendency to reversion may often check or prevent the work; but as this tendency has not prevented man from forming by selection numerous domestic races, why should it prevail against natural selection? 1872
selection. 1861 1866 1869
↑ 1 blocks not present in 1859 1860 1869 1872; present in 1861 1866
Non-inheritance of any new character is, in fact, the same thing as reversion to the character of the grandparents or more remote ancestors; and no doubt the tendency to reversion may often have checked or prevented the action of natural selection; but its importance has been greatly exaggerated by some writers.
→ the case of 1869 1872
man's 1859 1860 1861 1866
→ if the individuals be allowed freely to intercross, 1872
free intercrossing will wholly stop 1859 1860 1861 1866 1869
→ work will completely fail. 1872
work. 1859 1860 1861 1866 1869
→ that there is no separation of selected individuals. 1872
a large amount of crossing with inferior animals. 1859 1860 1861 1866 1869
→ OMIT 1872
as might be, natural selection will always tend to preserve 1859 1860 1861 1866
natural selection will always tend to preserve 1869
→ will tend to be preserved. 1872
so as better to fill up the unoccupied place. 1859 1860 1861 1866 1869
→ then, 1866 1869 1872
then 1859 1861
then if natural selection be modifying and improving a species in the several districts, there will be intercrossing with the other individuals of the same species on the confines of each. 1860
→ will in the long run generally be supplanted by one 1872
whether the result 1869
→ adjoining varieties. 1872
crossing of other varieties, or originally formed with an intermediate character, will in the long run generally be supplanted by one of the varieties on either hand. 1869
→ chiefly affect those animals 1872
most affect those animals 1859 1860 1861 1866
affect those animals most 1869
Circumstances
Circumstances
favourable
favourable
→ for the production of new forms through Natural Selection.
This is an extremely intricate subject. A
large
great
amount of →variability, under which term individual differences →are always included, will evidently be favourable. A large number of individuals, by giving a better chance →within any given period for the appearance of profitable variations, will compensate for a lesser amount of variability in each individual, and is, I believe,
an extremely
a highly
important element of success. Though
nature
Nature
grants
vast
long
periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are
striving,
striving
→OMIT to seize on each place in the economy of nature, if any one species does not become modified and improved in a corresponding degree with its competitors, it will
soon
....
be exterminated. Unless favourable variations be inherited by some at least of the offspring, nothing can be effected by natural →selection. The tendency to reversion may often check or prevent the work; but as this tendency has not prevented man from forming by selection numerous domestic races, why should it prevail against natural selection? ↑
In →the case of methodical selection, a breeder selects for some definite object, and →if the individuals be allowed freely to intercross, his →work will completely fail. But when many men, without intending to alter the breed, have a nearly common standard of perfection, and all try to
get
procure
and breed from the best animals,
much
....
improvement
and modification
....
surely but slowly
follow
follows
from this unconscious process of selection, notwithstanding →that there is no separation of selected individuals. Thus it will be
in
under
nature; for within a confined area, with some place in
its
the natural
polity not
so
....
perfectly
occupied
occupied,
→OMIT all the individuals varying in the right direction, though in different degrees, →will tend to be preserved. But if the area be
very large,
large,
its several districts will almost certainly present different conditions of life; and →then, if the same species undergoes modification in different
parts,
districts,
the newly-formed varieties will intercross on the confines of
each
each.
district.
....
But we shall see in the
seventh
sixth
chapter that intermediate varieties, inhabiting
an
....
intermediate
district,
districts,
→will in the long run generally be supplanted by one of the →adjoining varieties.
The
....
intercrossing
Intercrossing
will →chiefly affect those animals which unite for each
birth,
birth
which
and
wander much, and which do not breed at a very quick rate. Hence
in
with
animals of this nature, for
instance
instance,
in
....
birds, varieties will generally be confined to separated countries; and this I
believe
find
to be the case.
In
With
hermaphrodite organisms which cross only occasionally, and likewise
in
with
animals which unite for each