Comparison with 1872 |
|
But why
in
the case of distinct species, the sexual elements should so generally the case of distinct species, the sexual elements should so generally 1872 |
numerous species, descended from a common parent-form, the reproductive system should in all 1866 |
the case of species, the sexual elements should so generally 1869 |
have become more or less modified, leading to their mutual infertility, we do not
know; know; 1872 | know 1866 | know. 1869 |
but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life.
but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life.
1872 |
in the least; nor whether this has been effected directly, or in correlation with other structural and functional modifications. 1866 |
OMIT 1869 |
It is not surprising that the degree of
difficulty in uniting
two species, and the degree
of sterility of
their hybrid-offspring
should generally correspond, though
due to distinct causes; for both depend on the amount of difference of some kind
between the species which are crossed. Nor is it surprising that the facility of effecting a first cross, the
fertility of the hybrids produced,
and
the capacity of being grafted together— though this latter capacity evidently depends on widely different circumstances— should all run, to a certain extent, parallel with the systematic affinity of the forms which are
subjected to experiment; for systematic affinity attempts to express
all kinds
of resemblance between all species. ↑2 blocks not present in 1859 1860 1861 1872; present in 1866 1869 | It is not surprising that the degree of
difficulty in uniting
two species, and the degree
of sterility of
their hybrid-offspring, should generally
correspond, even if due to distinct causes; for both depend on the amount of difference of some kind
between the species which are crossed.
Nor is it surprising that the facility of effecting a first cross, and the fertility of the hybrids thus produced, and the capacity of being grafted together—though this latter capacity evidently depends on widely different circumstances—should all run, to a certain extent, parallel with the systematic affinity of the forms which are
subjected to experiment; for systematic affinity attempts to express
all kinds
of resemblance between all species.
|
|
|
First crosses between forms known to be varieties, or sufficiently alike to be considered as varieties, and their mongrel offspring, are very generally, but not
quite universally, fertile. Nor is this nearly general
and perfect fertility surprising, when
it is it is 1872 | we 1859 1860 1861 1866 1869 |
remembered remembered 1872 | remember 1859 1860 1861 1866 1869 |
how liable we are to argue in a circle with respect to varieties in a state of nature; and when we remember that the greater number of varieties have been produced under domesti- cation
by the selection of mere external differences, and not of differences in the reproductive system. Nor
should it
be forgotten
that long-continued domestication apparently
tends to eliminate sterility, and is therefore little likely to induce this same quality. Independently of the question of fertility, in all other respects there is the closest general resemblance between hybrids and
mongrels,— mongrels,— 1872 | mongrels, 1869 |
in their variability, in their power of absorbing each other by repeated crosses, and in their inheritance
|
But
why,
in
the case of species, the sexual elements should so generally the case of species, the sexual elements should so generally 1869 |
numerous species, descended from a common parent-form, the reproductive system should in all 1866 |
the case of distinct species, the sexual elements should so generally 1872 |
have become more or less modified, leading to their mutual infertility, we do not
know. know. 1869 | know 1866 | know; 1872 |
...OMIT 1869 |
in the least; nor whether this has been effected directly, or in correlation with other structural and functional modifications. 1866 |
but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life.
1872 |
↑1 blocks not present in 1866 1869; present in 1872 1859 1860 1861 | It is not surprising that the degree of
difficulty in uniting
two species, and the degree
of sterility of
their hybrid-offspring
should generally correspond, though
due to distinct causes; for both depend on the amount of difference of some kind
between the species which are crossed.
|
|
|
It is not surprising that the
..
difficulty in
crossing any crossing any 1869 | uniting 1866 |
two species, and the
sterility sterility 1869 | degree 1866 |
of
....... 1869 | sterility of 1866 |
their hybrid-offspring, should
in most cases in most cases 1869 |
generally 1866 |
correspond, even if due to distinct causes; for both depend on the amount of difference
...OMIT 1869 |
of some kind 1866 |
between the species which are crossed. Nor is it surprising that the facility of effecting a first cross, and the fertility of the hybrids thus produced, and the capacity of being grafted together—though this latter capacity evidently depends on widely different circumstances—should all run, to a certain extent, parallel with the systematic affinity of the forms
..
subjected to experiment; for systematic affinity
includes resemblances of includes resemblances of 1869 |
attempts to express 1866 |
all
kinds.
..
....... 1869 | resemblance 1866 |
..
..
..
|
|
First crosses between forms known to be varieties, or sufficiently alike to be considered as varieties, and their mongrel offspring, are very generally, but
not, not, 1861 1866 1869 1872 | not 1859 1860 |
as is so often stated, invariably as is so often stated, invariably 1869 1872 |
quite universally, 1859 |
quite uni- versally, 1860 |
as is so often falsely stated, universally 1861 |
as is so often stated, universally 1866 |
fertile. Nor is this
almost universal almost universal 1869 1872 | nearly general 1859 1860 1861 1866 |
and perfect fertility surprising, when
we we 1859 1860 1861 1866 1869 | it is 1872 |
remember remember 1859 1860 1861 1866 1869 | remembered 1872 |
how liable we are to argue in a circle with respect to varieties in a state of nature; and when we remember that the greater number of varieties have been produced under
domestication domestication 1860 1861 1866 1869 1872 | domesti- cation 1859 |
by the selection of mere external differences, and
that they have not been long exposed to uniform conditions of life. that they have not been long exposed to uniform conditions of life. 1869 1872 |
not of differences in the reproductive system. 1859 1860 1861 1866 |
It
should
also
be
especially kept in mind, especially kept in mind, 1869 1872 |
forgotten 1866 |
that long-continued domestication
....... 1869 1872 | apparently 1866 |
tends to eliminate sterility, and is therefore little likely to induce this same quality. Independently of the question of fertility, in all other respects there is the closest general resemblance between hybrids and
mongrels, mongrels, 1869 | mongrels,— 1872 |
in their variability, in their power of absorbing each other by repeated crosses, and in their inheritance
|