Origin of Species Variorum

→ OMIT 1869 1872

we plainly see that 1859 1860 1861 1866

→ which differ to a certain extent, 1869 1872

that is between members of different strains or sub-breeds, 1859 1860 1861 1866

→ offspring; and that close interbreeding continued during several generations between the nearest relations, especially if these be kept under the same conditions of life, almost always induces weakness and sterility. 1869

offspring. 1859 1860 1861 1866

offspring; 1872

↑ 1 blocks not present in 1869; present in 1859 1860 1861 1866 1872

I believe, indeed, from the facts alluded to in our fourth chapter, that a certain amount of crossing is indispensable even with hermaphrodites; and that close interbreeding continued during several generations between the nearest relations, especially if these be kept under the same conditions of life, always induces weakness and sterility in the progeny.

→ varied and become 1859 1860 1861 1866 1869

been subjected to 1872

→ give 1859 1860 1861 1866 1869

conditions, or which have slightly varied, give 1872

→ that greater changes, or changes of a particular nature, often render 1859 1860 1861 1866 1869

OMIT 1872

→ in some degree 1859 1860 1861 1866 1869

long habituated to certain uniform conditions under a state of nature, when subjected, as under confinement, to a considerable change in their conditions, very frequently are rendered more or less 1872

→ that greater crosses, that is 1859 1860 1861 1866 1869

we know that a 1872

→ males and females which 1859 1860 1861 1866 1869

two forms, that 1872

→ cannot persuade myself 1859 1860 1861 1866 1869

am fully persuaded 1872

→ parallelism is 1859 1860 1861 1866 1869

double parallelism is by no means 1872

→ life; this principle apparently being that life, as Mr. Herbert Spencer has remarked, depends on, or consists in, the incessant action and reaction of various forces, which, as throughout nature, are always tending towards an equilibrium; and when this tendency is slightly disturbed by any change, the vital forces apparently gain in power. 1869

life. 1859 1860 1861

life; this principle apparently being that life, as Mr. Herbert Spencer has remarked, depends on, or consists in, the incessant action and reaction of various forces, which, as throughout nature, are always tending towards an equilibrium; and when this ten- dency is slightly disturbed by any change, the vital forces apparently gain in power. 1866

life are beneficial to all living things. We see this acted on by farmers and gardeners in their frequent exchanges of seed, tubers, &c., from one soil or climate to another, and back again. During the convalescence of animals, →OMIT great benefit is derived from almost any change in

their

the

habits of life. Again, both with plants and animals, there is

the clearest

abundant

evidence,

evidence

that a cross between

very distinct

....

individuals of the same species, →which differ to a certain extent, gives vigour and fertility to the →offspring; and that close interbreeding continued during several generations between the nearest relations, especially if these be kept under the same conditions of life, almost always induces weakness and sterility. ↑

Hence it seems that, on the one hand, slight changes in the conditions of life benefit all organic beings, and on the other hand, that slight crosses, that is crosses between the males and females of the same

species

species,

which have →varied and become slightly

different

different,

→give vigour and fertility to the offspring.

But,

But

as we

have

seen,

seen

→that greater changes, or changes of a particular nature, often render organic beings →in some degree sterile; and →that greater crosses, that is

cross

crosses

between →males and females which have become widely or specifically different, produce hybrids which are

almost always

generally sterile

in some

degree sterile.

degree.

I →cannot persuade myself that this →parallelism is an accident or an illusion. Both series of facts seem to be connected together by some common but unknown bond, which is essentially related to the principle of →life; this principle apparently being that life, as Mr. Herbert Spencer has remarked, depends on, or consists in, the incessant action and reaction of various forces, which, as throughout nature, are always tending towards an equilibrium; and when this tendency is slightly disturbed by any change, the vital forces apparently gain in power.