Dear Sir

I am obliged by your note.¹

I agree with you that the reproductive system of natural species must have been in some way modified in correlation with the variation which they have undergone. But why has not a single domestic var. of an animal or plant, many of which have been profoundly modified, been rendered mutually sterile?²

Until this can be answered, it cannot be said that we know anything definitely.

As I have said I suspect that the difference is due to organisms in a state of nature having been exposed for long periods to much more uniform conditions, than are those under domestication.—³

Dear Sir | Yours faithfully | Ch. Darwin