Origin of Species Variorum

→ hybrids — Sterility 1859 1860 1861 1869 1872

hybrids—Sterility 1866

→ domestication — Laws 1859 1860 1861 1869 1872

domestication—Laws 1866

→ hybrids — Sterility 1859 1860 1861 1869 1872

hybrids—Sterility 1866

→ not accumulated by natural selection — Causes 1869 1872

— Causes 1859 1860 1861

not accumulated by natural selection—Causes 1866

→ hybrids — Parallelism 1859 1860 1861 1869 1872

hybrids—Parallelism 1866

→ of crossing — Dimorphism and trimorphism — Fertility 1869 1872

crossing — Fertility 1859 1860

of crossing — Fertility 1861

of crossing—Dimorphism and trimorphism—Fertility 1866

→ universal — Hybrids 1859 1860 1861 1869 1872

universal—Hybrids 1866

→ fertility — Summary. 1859 1860 1861 1869 1872

fertility—Summary. 1866

→ OMIT 1869 1872

the quality of 1859 1860 1861 1866

→ within the same country 1859 1860 1861 1866 1869

living together 1872

→ by the continued 1869

as I shall show, by the 1872

→ is, as I hope to show, incidental on 1869

is an incidental result of 1872

↑ 3 blocks not present in 1869 1872; present in 1859 1860 1861 1866

The importance of the fact that hybrids are very generally sterile, has, I think, been much underrated by some late writers. On the theory of natural selection the case is especially important, inasmuch as the sterility of hybrids could not possibly be of any advantage to them, and therefore could not have been acquired by the continued preservation of successive profitable degrees of sterility. I hope, however, to be able to show that sterility is not a specially acquired or endowed quality, but is incidental on other acquired differences.

CHAPTER

IX.

VIII.

HYBRIDISM.

Distinction between the sterility of first crosses and of →hybrids — Sterility various in degree, not universal, affected by close

inter-breeding,

interbreeding,

removed by →domestication — Laws governing the sterility of →hybrids — Sterility not a special endowment, but incidental on other

differences

differences,

→not accumulated by natural selection — Causes of the sterility of first crosses and of →hybrids — Parallelism between the effects of changed conditions of life and →of crossing — Dimorphism and trimorphism — Fertility of varieties when crossed and of their mongrel offspring not →universal — Hybrids and mongrels compared independently of their →fertility — Summary.

THE view

commonly

generally

entertained by naturalists is that species, when intercrossed, have been specially endowed with →OMIT sterility, in order to prevent

the

confusion

all

organic

forms.

This view certainly seems at first

probable,

highly probable,

for species →within the same country could hardly have

kept

been kept

distinct had they been capable of

crossing

....

freely.

freely crossing.

The subject is in many ways important for us, more especially as the sterility of species when first crossed, and that of their hybrid offspring, cannot have been

acquired,

acquired

→by the continued preservation of

successive

successive,

profitable degrees of sterility. It →is, as I hope to show, incidental on differences in the reproductive

systems

system

of the

parent-species.

parent-species,

~~and~~