Mr. Galton has pointed out that existing races and existing organs are
only kept at their present high pitch of organic excellence by the
stringent and incessant action of natural or artificial selection; and
the simple relaxation or withdrawal of such selective influences will
almost necessarily result in a certain amount of deterioration,
independently even of the principle of economy.[21] I think that this
cessation of a previous selective process will account for the
drooping--but _not diminished_--ears of various domesticated animals
(human preference and increased weight evidently aiding), and also for
the inferior instincts seen in them and in artificially-fed caterpillars
of the silk-moth, which now "often commit the strange mistake of
devouring the base of the leaf on which they are feeding, and
consequently fall down." Anyhow, I fail to see that anything is proved
by this latter case, except that natural instinct may be perverted or
aborted under unnatural conditions and a changed method of selection
which abolishes the powerful corrective formerly supplied by natural
selection.