edulously trained and carefully matched.

In the foregoing cases we have supposed that a sudden variation,
conspicuous enough to catch a fancier's eye, first appeared; but even this
degree of abruptness in the process of variation is not necessary for the
formation of a new breed. When the same kind of pigeon has been kept pure,
and has been bred during a long period by two or more fanciers, slight
differences in the strain can often be recognised. Thus I have seen
first-rate jacobins in one man's possession which certainly {218} differed
slightly in several characters from those kept by another. I possessed some
excellent barbs descended from a pair which had won a prize, and another
lot descended from a stock formerly kept by that famous fancier Sir John
Sebright, and these plainly differed in the form of the beak; but the
differences were so slight, that they could hardly be described by words.
Again, the common English and Dutch tumbler differ in a somewhat greater
degree, both in length of beak and shape of head. What first caused these
slight differences cannot be explained any more than why one man has a long
nose and another a short one. In the strains long kept distinct by
different fanciers, such differences are so common that they cannot be
accounted for by the accident of the birds first chosen for breeding having
been originally as different as they now are. The explanation no doubt lies
in selection of a slightly different nature having been applied in each
case; for no two fanciers have exactly the same taste, and consequently no
two, in choosing and carefully matching their birds, prefer or select
exactly the same. As each man naturally admires his own birds, he goes on
continually exaggerating by selection whatever slight peculiarities they
may possess. This will more especially happen with fanciers living in
different countries, who do not compare their stocks and aim at a common
standard of perfection. Thus, when a mere strain has once been formed,
unconscious selection steadily tends to augment the amount of difference,
and thus converts the strain into a sub-breed, and this ultimately into a
well-marked breed or race.

The principle of correlation of growth should never be lost sight of. Most
pigeons have small feet, apparently caused by their lessened use, and from
correlation, as it would appear, their beaks have likewise become reduced
in length. The beak is a conspicuous organ, and, as soon as it