TO C.LYELL.Ilkley, October 31st [1859].
That you may not misunderstand how far I go with Pallas and his many disciples I should like to add that, though I believe that our domestic dogs have descended from several wild forms, and though I must think that the sterility, which they would probably have evinced, if crossed before being domesticated, has been eliminated, yet I go but a very little way with Pallas & Co.

in their belief in the importance of the crossing and blending of the aboriginal stocks.

(80/1.

"With our domesticated animals, the various races when crossed together are quite fertile; yet in many cases they are descended from two or more wild species.

From this fact we must conclude either that the aboriginal parent-species at first produced perfectly fertile hybrids, or that the hybrids subsequently reared under domestication became quite fertile.
This latter alternative, which was first propounded by Pallas, seems by far the most probable, and can, indeed, hardly be doubted" ("Origin of Species," Edition VI., page 240).) You will see this briefly put in the first chapter.