Origin of Species Variorum

→ in all cases connects 1869 1872

connecting in all cases 1866

→ clearly leads to the conclusion that 1869 1872

drive us to conclude that in all cases 1866

→ the sterility of crossed species is confined to differences in their sexual elements. 1872

sterility, both in the parents and in the offspring, is confined to differences in their reproductive systems. 1866

the sterility is confined to dif- ferences in the sexual elements. 1869

→ 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

→ 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

→ in most cases correspond, even if 1872

generally correspond, though 1859 1860 1861

→ OMIT 1872

of some kind 1859 1860 1861

→ and 1859 1872

from it, and 1860 1861

→ includes resemblances of 1872

attempts to express 1859 1860 1861

↑ 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.

→ 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

→ 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

→ especially kept in mind, 1869 1872

forgotten 1866

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

In all other respects, excluding fertility, there is a close general resemblance between hybrids and mongrels.

→ although we are as ignorant of the precise cause of the sterility of first crosses and of hybrids as we are why animals and plants removed from their natural conditions become sterile, yet the facts 1872

the facts briefly 1859 1860

although we are profoundly ignorant in every case of the precise cause of sterility, the facts briefly 1861

although we are profoundly ignorant in every case of the precise cause of the sterility of first crosses and of hybrids, the facts briefly 1866

although we are profoundly ignorant of the precise cause of the sterility of first crosses and of hybrids, the facts 1869

→ to the belief that species aboriginally existed as varieties. 1872

to, but even rather to support the view, that there is no fundamental distinction between species and varieties. 1859 1860

to, but even rather to support in some respects the view, that there is no fundamental distinction between species and varieties. 1861

to the view, that there is no fundamental distinction between species and varieties. 1866

to the belief that varieties and species are not fundamentally different. 1869

the sterility of the illegitimate unions of dimorphic and trimorphic plants and of their illegitimate progeny,

render

perhaps render

it probable that

there is

....

some unknown bond →in all cases connects the degree of fertility of first unions with that of their offspring. The consideration of these facts on dimorphism, as well as

the

of the

results of reciprocal crosses, →clearly leads to the conclusion that the primary cause of →the sterility of crossed species is confined to differences in their sexual elements. But

why

why,

in →the case of distinct species, the sexual elements should so generally have become more or less modified, leading to their mutual infertility, we do not

know

know.

know;

→ 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. It is not surprising that the

degree of

....

difficulty in

uniting

crossing any

two species, and the

degree

sterility

sterility of

....

their

hybrid-offspring

hybrid-offspring,

hybrid offspring,

should →in most cases correspond, even if due to distinct causes; for both depend on the amount of difference →OMIT between the species which are crossed. Nor is it surprising that the facility of effecting a first cross,

the

and the

fertility of the hybrids

produced,

produced

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 →includes resemblances of all

kinds

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

not,

→as is so often stated, invariably fertile. Nor is this

nearly general

almost universal

and perfect fertility surprising, when

it is

remember

remembered

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

domestication

by the selection of mere external differences, and →that they have not been long exposed to uniform conditions of life.

Nor

should

also

be →especially kept in mind, 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,—

in their variability, in their power of absorbing each other by repeated crosses, and in their inheritance of characters from both parent-forms. ↑ Finally, then, →although we are as ignorant of the precise cause of the sterility of first crosses and of hybrids as we are why animals and plants removed from their natural conditions become sterile, yet the facts given in this chapter do not seem to me opposed →to the belief that species aboriginally existed as varieties.