has often been noticed that the dovecote pigeon seems to have an actual
aversion towards the several fancy breeds (16/8. 'The Dovecote' by the Rev.
E.S. Dixon page 155; Bechstein 'Naturgesch. Deutschlands' b. 4 1795 page 17.)
yet all have certainly sprung from a common progenitor. The Rev. W.D. Fox
informs me that his flocks of white and common Chinese geese kept distinct.

These facts and statements, though some of them are incapable of proof,
resting only on the opinion of experienced observers, show that some domestic
races are led by different habits of life to keep to a certain extent
separate, and that others prefer coupling with their own kind, in the same
manner as species in a state of nature, though in a much less degree.

[With respect to sterility from the crossing of domestic races, I know of no
well-ascertained case with animals. This fact, seeing the great difference in
structure between some breeds of pigeons, fowls, pigs, dogs, etc., is
extraordinary, in contrast with the sterility of many closely allied natural
species when crossed; but we shall hereafter attempt to show that it is not so
extraordinary as it at first appears. And it may be well here to recall to
mind that the amount of external difference between two species is not a safe
guide for predicting whether or not they will breed together,--some closely
allied species when crossed being utterly sterile, and others which are
extremely unlike being moderately fertile. I have said that no case of
sterility in crossed races rests on satisfactory evidence; but here is one
which at first seems trustworthy. Mr. Youatt (16/9. 'Cattle' page 202.) and a
better authority cannot be quoted, states, that formerly in Lancashire crosses
were frequently made between longhorn and shorthorn cattle; the first cross
was excellent, but the produce was uncertain; in the third or fourth
generation the cows were bad milkers; "in addition to which, there was much
uncertainty whether the cows would conceive; and full one-third of the cows
among some of these half-breds failed to be in calf." This at first seems a