Origin of Species Variorum

→ including of course the reproductive systems, having 1872

having 1859 1860 1861 1866 1869

→ does not diminish; it is even apt to increase, this being generally the result, as before explained, of too close interbreeding. 1869 1872

rarely diminishes. 1859 1860 1861

does not diminish, but is apt to increase; this increase being perhaps intelligible, as before explained, on the principles of inheritance and from too close interbreeding. 1866

→ OMIT 1872

so like in every respect to that of hybrids, 1866

(as will be immediately explained) 1869

→ OMIT 1872

of 1866

when individuals belonging to 1869

→ OMIT 1872

species (as will be immediately described), 1866

form are united, 1869

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

It should, however, be borne in mind that the sterility of these plants has been acquired for a special purpose, and may differ in origin from that of hybrids.

→ the above or any other view, 1869 1872

vague hypotheses, 1859 1860 1861

this or any other view, 1866

→ having 1859 1860 1861 1872

or constitution having 1866 1869

→ A 1869 1872

It may seem fanciful, but I suspect that a 1859 1860 1861 1866

→ holds good with 1872

extends to 1859 1860 1861 1866

apparently extends to 1869

→ which I have elsewhere given, that 1872

that 1859 1860 1861 1866 1869

→ 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; 1872

offspring. 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

→ OMIT 1872

I believe, indeed, from the facts alluded to in our fourth chapter, that a certain amount of crossing is indispensable even with hermaphrodites; 1859 1860 1861 1866

by us; in the other case, or that of hybrids, the external conditions have remained the same, but the organisation has been disturbed by two

different

distinct

structures and

constitutions

constitutions,

→including of course the reproductive systems, having been blended into one. For it is scarcely possible that two organisations should be compounded into one, without some disturbance occurring in the development, or periodical action, or mutual

relation

relations

of the different parts and organs one to

another,

another

or to the conditions of life. When hybrids are able to breed inter

se,

se ,

they transmit to their offspring from generation to generation the same

com- pounded

compounded

organisation, and hence we need not be surprised that their sterility, though in some degree

vari- able,

variable,

→does not diminish; it is even apt to increase, this being generally the result, as before explained, of too close interbreeding. The above view of the sterility of hybrids being caused by two

different

....

constitutions

having been

being

confounded

compounded

into one has

lately

....

been strongly maintained by Max

Wichura;

but

must

owned

that

the

sterility,

sterility

....

→OMIT

which

....

affects

....

the

....

illegitimate offspring

offspring

dimorphic

and

trimorphic

plants

plants,

....

→OMIT

the

....

same

....

→OMIT

makes

this

view

rather

doubtful.

↑

must

must,

also

~~however,~~

however,

confessed

owned

that we cannot understand,

excepting

except

....

on →the above or any other view, several facts with respect to the sterility of hybrids; for instance, the unequal fertility of hybrids produced from reciprocal crosses; or the increased sterility in those hybrids which occasionally and exceptionally resemble closely either pure parent. Nor do I pretend that the foregoing remarks go to the root of the

matter:

matter;

no explanation is offered why an organism, when placed under unnatural conditions, is rendered sterile. All that I have attempted to

show,

show

is,

that in two cases, in some respects allied, sterility is the common

result, —

result,—in

result,—

the one case from the conditions of life having been disturbed, in the other case from the organisation →having been disturbed by two organisations

having been

being

compounded into one.

→A similar parallelism →holds good with an allied yet very different class of facts. It is an old and almost universal

belief,

belief

founded,

founded

I think,

....

on a considerable body of evidence, →which I have elsewhere given, that slight changes in the conditions of 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

the

their

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

abundant

the clearest

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; →OMIT and that close

inter-breeding

interbreeding

continued during several generations