Comparison with 1866 |
|
occasional intercross with a
distinct individual
is a law
of nature. I am well aware that there are, on this view, many cases of difficulty, some of which I am trying to investigate. Finally then, we may conclude that in many organic beings, a cross between two individuals is an obvious necessity for each birth; in many others it occurs perhaps only at long intervals; but in none, as I suspect, can self-fertilisation go on for perpetuity. |
Circumstances
favourable
to Natural Selection.
to Natural Selection. 1866 |
to Natural Selection
.—
1859 |
to Natural Selection.
—
1860 1861 |
for the production of new forms through Natural Selection.
1869 |
for the production of new forms through Natural Selection. 1872 |
|
This is an extremely intricate subject. A
large large 1859 1860 1861 1866 | great 1869 1872 |
amount of
variability will evidently be favourable for the work of natural selection, but mere variability will evidently be favourable for the work of natural selection, but mere 1861 1866 |
inheritable and diversified variability is favourable, but I believe mere 1859 1860 |
variability, under which term 1869 1872 |
individual differences
probably suffice. probably suffice. 1861 1866 |
suffice for the work. 1859 1860 |
are always included, will evidently be favourable. 1869 1872 |
A large number of individuals, by giving a better chance
for the appearance within any given period of profitable variations, 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 |
within any given period for the appearance of profitable variations, 1872 |
will compensate for a lesser amount of variability in each individual, and is, I believe, an extremely
important element of success. Though nature
grants
vast vast 1859 1860 1861 1866 | long 1869 1872 |
periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are striving,
it may be said,
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 soon 1859 1860 1861 1866 | soon 1869 1872 |
be exterminated. Unless favourable variations be inherited by some at least of the offspring, nothing can be effected by natural selection. 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.
If the
tendency to reversion
has has 1861 1866 |
may often check or prevent the work; but as this tendency has 1869 |
not prevented man from
creating innumerable hereditary races in the animal and vegetable kingdoms, creating innumerable hereditary races in the animal and vegetable kingdoms, 1861 1866 |
forming by selection numerous domestic races, 1869 |
why should it
have stopped the process of have stopped the process of 1861 1866 |
prevail against 1869 |
natural selection? |
|
In
man's man's 1859 1860 1861 1866 |
the case of 1869 1872 |
methodical selection, a breeder selects for some definite object, and free intercrossing will wholly stop
|
occasional intercross
with a with a 1859 1860 1861 1866 1869 | between 1872 |
distinct
individual individual 1859 1860 1861 1866 1869 | individuals 1872 |
is a
law law 1859 1860 1861 1866 1869 |
very general, if not universal, law 1872 |
of nature. I am well aware that there are, on this view, many cases of difficulty, some of which I am trying to investigate. Finally then, we may conclude that in many organic beings, a cross between two individuals is an obvious necessity for each birth; in many others it occurs perhaps only at long intervals; but in none, as I suspect, can self-fertilisation go on for perpetuity. |
Circumstances
Circumstances
1866 1869 1872 |
Circumstances
1859 1860 1861 |
favourable
favourable
1866 1869 1872 |
favourable
1859 1860 1861 |
for the production of new forms through Natural Selection.
for the production of new forms through Natural Selection.
1869 |
to Natural Selection
.—
1859 |
to Natural Selection.
—
1860 1861 |
to Natural Selection. 1866 |
for the production of new forms through Natural Selection. 1872 |
|
This is an extremely intricate subject. A
great great 1869 1872 | large 1859 1860 1861 1866 |
amount of
variability, under which term 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 |
individual differences
are always included, will evidently be favourable. are always included, will evidently be favourable. 1869 1872 |
suffice for the work. 1859 1860 |
probably suffice. 1861 1866 |
A large number of individuals, by giving a better chance
for the appearance of profitable variations within any given period, for the appearance of profitable variations within any given period, 1869 |
for the appearance within any given period of profitable variations, 1859 1860 1861 1866 |
within any given period for the appearance of profitable variations, 1872 |
will compensate for a lesser amount of variability in each individual, and is, I believe,
an extremely an extremely 1859 1860 1861 1866 1869 | a highly 1872 |
important element of success. Though
Nature Nature 1861 1866 1869 1872 | nature 1859 1860 |
grants
long long 1869 1872 | vast 1859 1860 1861 1866 |
periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are
striving striving 1861 1866 1869 1872 | striving, 1859 1860 |
...OMIT 1861 1866 1869 1872 |
it may be said, 1859 1860 |
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
....... 1869 1872 | soon 1859 1860 1861 1866 |
be exterminated. Unless favourable variations be inherited by some at least of the offspring, nothing can be effected by natural
selection. selection. 1861 1866 1869 |
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 |
↑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
tendency to reversion
may often check or prevent the work; but as this tendency has may often check or prevent the work; but as this tendency has 1869 |
has 1861 1866 |
not prevented man from
forming by selection numerous domestic races, forming by selection numerous domestic races, 1869 |
creating innumerable hereditary races in the animal and vegetable kingdoms, 1861 1866 |
why should it
prevail against prevail against 1869 |
have stopped the process of 1861 1866 |
natural selection? |
|
In
the case of the case of 1869 1872 |
man's 1859 1860 1861 1866 |
methodical selection, a breeder selects for some definite object, and
free intercrossing will wholly stop free intercrossing will wholly stop 1859 1860 1861 1866 1869 |
if the individuals be allowed freely to intercross, 1872 |
|