Origin of Species Variorum

Comparison with 1859

Text in this page (from paragraph 5200, sentence 320, word 27 to paragraph 5210, sentence 200, word 68) is not present in 1859

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 quite universally, fertile. Nor is this nearly general and perfect fertility surprising, when we remember 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 by the selection of mere external differences, and not of differences in the reproductive system.

Text in this page (from paragraph 5300, sentence 210 to paragraph 5300, sentence 210, word 21) is not present in 1859

of sterility, both in the parents and in the offspring, is confined to differences in their reproductive systems. But why in numerous species, descended from a common parent-form, the reproductive system should in all have become more or less modified, leading to their mutual infertility, we do not know in the least; nor whether this has been effected directly, or in correlation with other structural and functional modifications. ↑

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.

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, as is so often stated, universally fertile. Nor is this nearly general and perfect fertility surprising, when we remember 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 domestication by the selection of mere external differences, and not of differences in the reproductive system. Nor should it be forgotten that long-continued domestication apparently tends to eliminate sterility, and is therefore little likely to induce this