Comparison with 1872 |
|
failed, after consultation with one of the highest authorities, namely, Professor Huxley, to discover a single
...OMIT 1872 |
case of an 1859 1860 1861 1866 1869 |
hermaphrodite animal with the organs of reproduction so perfectly enclosed
...OMIT 1872 |
within the body, 1859 1860 1861 1866 1869 |
that access from
without, without, 1872 | without 1859 1860 1861 1866 1869 |
and the occasional influence of a distinct
individual, individual, 1872 | individual 1859 1860 1861 1866 1869 |
can be shown to be physically impossible. Cirripedes long appeared to me to
present, present, 1872 | present 1859 1860 1861 1866 1869 |
...OMIT 1872 |
a case of very great difficulty 1859 1860 1861 1866 1869 |
under this point of
view, view, 1872 | view; 1859 1860 1861 1866 1869 |
a case of great difficulty; but a case of great difficulty; but 1872 |
but 1859 1860 1861 1866 1869 |
I have been enabled, by a fortunate chance,
....... 1872 | elsewhere 1859 1860 1861 1866 1869 |
to prove that two individuals, though both are self-fertilising hermaphrodites, do sometimes cross. |
|
It must have struck most naturalists as a strange anomaly that,
both with both with 1872 |
in the case of both 1859 1860 1861 1866 1869 |
animals and plants,
some species some species 1872 | species 1859 1860 1861 1866 1869 |
of the same family and even of the same genus, though agreeing closely with each other in
....... 1872 | almost 1859 1860 1861 1866 1869 |
their whole organisation,
....... 1872 | yet 1859 1860 1861 1866 1869 |
are
...OMIT 1872 |
not rarely, some of them 1859 1860 1861 1866 1869 |
hermaphrodites, and some
....... 1872 | of them 1859 1860 1861 1866 1869 |
unisexual. But if, in fact, all hermaphrodites do occasionally
intercross, intercross, 1872 | intercross 1859 1860 1861 1866 1869 |
...OMIT 1872 |
with other individuals, 1859 1860 1861 1866 1869 |
the difference between
them them 1872 | hermaphrodites 1859 1860 1861 1866 1869 |
and unisexual
species species 1872 | species, 1859 1860 1861 1866 1869 |
is, as is, as 1872 | as 1859 1860 1861 1866 1869 |
far as function is concerned,
....... 1872 | becomes 1859 1860 1861 1866 1869 |
very small. |
|
From these several considerations and from the many special facts which I have collected, but which I am
unable unable 1872 | not 1859 1860 1861 1866 1869 |
here
....... 1872 | able 1859 1860 1861 1866 1869 |
to give,
it appears that with animals and plants it appears that with animals and plants 1872 |
I am strongly inclined to suspect that, both in the vegetable and animal kingdoms, 1859 1860 1861 |
I am strongly inclined to suspect, that, both in the vegetable and animal kingdoms, 1866 1869 |
an occasional intercross
between between 1872 | with a 1859 1860 1861 1866 1869 |
distinct
individuals individuals 1872 | individual 1859 1860 1861 1866 1869 |
is a
very general, if not universal, law very general, if not universal, law 1872 |
law 1859 1860 1861 1866 1869 |
of nature. ↑2 blocks not present in 1872; present in 1859 1860 1861 1866 1869 | 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. 1872 |
to Natural Selection
.—
1859 |
to Natural Selection.
—
1860 1861 |
to Natural Selection. 1866 |
for the production of new forms through Natural Selection.
1869 |
|
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
within any given period for the appearance of profitable variations, 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 |
will compensate for a lesser amount of variability in each individual, and is, I believe,
a highly a highly 1872 | an extremely 1859 1860 1861 1866 1869 |
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.
↑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.
|
|
|
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
if the individuals be allowed freely to intercross, if the individuals be allowed freely to intercross, 1872 |
free intercrossing will wholly stop 1859 1860 1861 1866 1869 |
his
work will completely fail. work will completely fail. 1872 |
work. 1859 1860 1861 1866 1869 |
But when many men, without intending to alter the breed, have a nearly common standard of perfection, and all try to
procure procure 1869 1872 | get 1859 1860 1861 1866 |
and breed from the best animals,
....... 1872 | much 1859 1860 1861 1866 1869 |
improvement
....... 1869 1872 | and modification 1859 1860 1861 1866 |
surely but slowly
follows follows 1869 1872 | follow 1859 1860 1861 1866 |
from this unconscious process of selection, notwithstanding
that there is no separation of selected individuals. that there is no separation of selected individuals. 1872 |
a large amount of crossing with inferior animals. 1859 1860 1861 1866 1869 |
Thus it will be
under under 1872 | in 1859 1860 1861 1866 1869 |
nature; for within a confined area, with some place in
the natural the natural 1872 | its 1859 1860 1861 1866 1869 |
polity not
....... 1869 1872 | so 1859 1860 1861 1866 |
perfectly
occupied, occupied, 1869 1872 | occupied 1859 1860 1861 1866 |
...OMIT 1872 |
as might be, natural selection will always tend to preserve 1859 1860 1861 1866 |
natural selection will always tend to preserve 1869 |
all the individuals varying in the right direction, though in different degrees,
will tend to be preserved. will tend to be preserved. 1872 |
so as better to fill up the unoccupied place. 1859 1860 1861 1866 1869 |
But if the area be large,
its several districts will almost certainly present different conditions of life; and
then, 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 |
|
Text in this page (from paragraph 2900, sentence 400a to paragraph 2900, sentence 500, word 12) is not present in 1872 |