onditions of life, inducing further variability or reversion to long-lost
characters, it may apparently last for an enormous period. We may infer
that this is the case from the high antiquity of certain races; but some
caution is necessary on this head, for the same variation may appear
independently after long intervals of time, or in distant places. We may
safely assume that this has occurred with the turnspit-dog which is figured
on the ancient Egyptian monuments, with the solid-hoofed swine[938]
mentioned by Aristotle, with five-toed fowls {429} described by Columella,
and certainly with the nectarine. The dogs represented on the Egyptian
monuments, about 2000 B.C., show us that some of the chief breeds then
existed, but it is extremely doubtful whether any are identically the same
with our present breeds. A great mastiff sculptured on an Assyrian tomb,
640 B.C., is said to be the same with the dog still imported into the same
region from Thibet. The true greyhound existed during the Roman classical
period. Coming down to a later period, we have seen that, though most of
the chief breeds of the pigeon existed between two and three centuries ago,
they have not all retained to the present day exactly the same character;
but this has occurred in certain cases in which improvement was not
desired, for instance in the case of the Spot or the Indian ground-tumbler.

De Candolle[939] has fully discussed the antiquity of various races of
plants; he states that the black-seeded poppy was known in the time of
Homer, the white-seeded sesamum by the ancient Egyptians, and almonds with
sweet and bitter kernels by the Hebrews; but it does not seem improbable
that some of these varieties may have been lost and reappeared. One variety
of barley and apparently one of wheat, both of which were cultivated at an
immensely remote period by the Lake-inhabitants of Switzerland, still
exist. It is said[940] that "specimens of a small variety of gourd which is
still common in the market of Lima were exhumed from an ancient cemetery in
Peru." De Candolle remarks that, in the books and drawings of the sixteenth
century, the principal races of the cabbage, turnip, and gourd can be
recognised; this might have been expected at so late a period, but whether
any of these plants are absolutely identical with our present sub-varieties
is not certain. It is, however, said that the Brussels sprout, a variety
which in some places is liable to degeneration