Origin of Species Variorum

→ in the same community of 1872

of 1859 1860 1861 1866 1869

→ ants; 1872

in the same community of ants; 1859 1860 1861 1866

ants in the same community; 1869

→ distinct kinds of trees 1872

trees 1859 1860 1861

distinct trees 1866 1869

→ reciprocally,— 1869 1872

are crossed reciprocally; 1859 1860 1861

are crossed reciprocally,— 1866

→ from each other in no respect 1872

in no respect from each other 1866 1869

→ has been asserted by so many authors to be universal, this cannot 1861 1866 1869 1872

cannot 1859 1860

→ as quite correct after the facts given on the high authority of Gärtner and Kölreuter. 1872

as universal; nor is their very general fertility surprising when we remember that it is not likely that either their constitutions or their reproductive systems should have been profoundly modified. 1859 1860

correct after the facts given on the authority of Gärtner and Kölreuter. 1861 1866 1869

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

Nor is the very general fertility of varieties, when crossed, surprising, when we remember that it is not likely that their reproductive systems should have been profoundly modified.

→ Most of the varieties which 1872

Moreover, most of the varieties which 1859 1860 1866 1869

Nor is the very general fertility of varieties, when crossed, surprising, when we remember that it is not likely that either their constitutions or their reproductive systems should 1861

→ experimented on 1866 1869 1872

experimentised on 1859 1860

profoundly modified. Moreover, most of the varieties which 1861

→ produced 1859 1860 1866 1869 1872

experimented on have been produced 1861

→ (I do not mean mere confinement) almost certainly 1866 1869 1872

apparently 1859

(I do not mean mere confinement) apparently 1860 1861

→ that sterility which, judging from analogy, would have affected the parent-species if intercrossed, 1872

sterility, 1859 1860 1861 1866 1869

→ that domestication would likewise induce sterility in their modified descendants when crossed. 1872

it also to produce sterility. 1859 1860 1861 1866 1869

the existence →in the same community of two or three defined castes of workers or sterile

females

female

→ants; but I have attempted to show how

this

these

difficulty

difficulties

can be mastered.

With respect to the almost universal sterility of species when first crossed, which forms so remarkable a contrast with the almost universal fertility of varieties when crossed, I must refer the reader to the recapitulation of the facts given at the end of the

eighth

ninth

chapter, which seem to me conclusively to show that this sterility is no more a special endowment than is the incapacity of two →distinct kinds of trees to be grafted

together,

together;

but that it is incidental on

constitutional

....

differences

confined to

the reproductive systems of the intercrossed species. We see the truth of this conclusion in the vast difference in the

result,

results

when

of crossing

the same two species →reciprocally,— that is, when one species is first used as the father and then as the

mother:

mother.

analogy

Analogy

from the consideration of dimorphic and trimorphic plants clearly leads

us to

the same conclusion, for when the forms are illegitimately united, they yield few or no seed, and their offspring are more or less sterile; and these forms

belong to

the same undoubted

species

species,

~~and~~

and

differ →from each other in no respect except in their reproductive organs and functions.

The

Although the

fertility of varieties when intercrossed and of their mongrel offspring →has been asserted by so many authors to be universal, this cannot be considered →as quite correct after the facts given on the high authority of Gärtner and Kölreuter. ↑ →Most of the varieties which have been →experimented on have been →produced under domestication; and as domestication →(I do not mean mere confinement) almost certainly tends to eliminate →that sterility which, judging from analogy, would have affected the parent-species if intercrossed, we ought not to expect →that domestication would likewise induce sterility in their modified descendants when crossed. This elimination of sterility apparently follows from the same cause which allows our domestic animals to breed freely under diversified circumstances; and this again apparently follows from their having been gradually accustomed to frequent changes in their conditions of life.

A double and parallel series of facts seems to throw much light on the sterility of species, when first crossed, and of their hybrid offspring. On the one side, there is good reason to believe that slight changes in the conditions of life give vigour and fertility to all organic beings. We know also that a cross between the distinct individuals of the same variety, and between distinct varieties, increases the number of their offspring, and certainly gives to them