cks. (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. Generally, with respect to crossing, the effects may be
diametrically opposite. If you cross two very distinct races, you may
make (not that I believe such has often been made) a third and new
intermediate race; but if you cross two exceedingly close races, or two
slightly different individuals of the same race, then in fact you annul
and obliterate the difference. In this latter way I believe crossing is
all-important, and now for twenty years I have been working at flowers
and insects under this point of view. I do not like Hooker's terms,
centripetal and centrifugal (80/2. Hooker's "Introductory Essay to the
Flora of Tasmania," pages viii. and ix.): they remind me of Forbes' bad
term of Polarity. (80/3. Forbes, "On the Manifestation of Polarity in
the Distribution of Organised Beings in Time."--"R. Institution Proc."
I., 1851-54.)

I daresay selection by man would generally work quicker than Natural
Selection; but the important distinction between them is, that man can
scarcely select except external and visible characters, and secondly, he
selects for his own good; whereas under nature, characters of all kinds
are selected exclusively for each creature's own good, and are well
exercised; but you will find all this in Chapter IV.

Although the hound, greyhound, and bull-dog may possibly have descended
from three distinct stocks, I am convinced that their present great
amount of difference is mainly due to the same causes which have made
the breeds of pigeons so different from each other, though these breeds
of pigeons have all descended from one wild stock; so that the Pallasian
doctrine I look at as but of quite secondary importance.

In my bigger book I have explained my meaning fully; whether I have in
the Abstract I cannot remember.

LETTER 81. TO C. LYELL. [December 5th, 1859.]

I forget whether you take in the "Ti