single
peculiarity or characteristic of any kind, bodily or mental, in which
offspring may not vary to a certain extent from the parent and other
animals.

Among ourselves this is well known. The simplest physical peculiarity is
mostly reproduced. I know a case of a man whose wife has the lobe of
one of her ears a little flattened. An ordinary observer might scarcely
notice it, and yet every one of her children has an approximation to the
same peculiarity to some extent. If you look at the other extreme, too,
the gravest diseases, such as gout, scrofula, and consumption, may be
handed down with just the same certainty and persistence as we noticed
in the perpetuation of the bandy legs of the Ancon sheep.

However, these facts are best illustrated in animals, and the extent
of the variation, as is well known, is very remarkable in dogs. For
example, there are some dogs very much smaller than others; indeed, the
variation is so enormous that probably the smallest dog would be about
the size of the head of the largest; there are very great variations in
the structural forms not only of the skeleton but also in the shape of
the skull, and in the proportions of the face and the disposition of the
teeth.

The Pointer, the Retriever, Bulldog, and the Terrier, differ very
greatly, and yet there is every reason to believe that every one
of these races has arisen from the same source,--that all the most
important races have arisen by this selective breeding from accidental
variation.

A still more striking case of what may be done by selective breeding,
and it is a better case, because there is no chance of that partial
infusion of error to which I alluded, has been studied very carefully by
Mr. Darwin,--the case of the domestic pigeons. I dare say there may
be some among you who may be pigeon 'fanciers', and I wish you to
understand that in approaching the subject, I would speak with all
humility and hesitation, as I regret to say that I am not a pigeon
fancier. I know it is a great art and mystery, and a thing upon which
a man must not speak lightly; but I shall endeavour, as far as
my understanding goes, to give you a summary of the published and
unpublished information which I have gained from Mr. Darwin.

Among the enormous variety,--I believe there are somewhere about a
hundred and fifty kinds of pigeons,--there are four kinds which may
be selected as representing the extremest divergences of one kind from
another.