so hasten the elimination of
disused and useless parts.

DROOPING EARS AND DETERIORATED INSTINCTS.

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.

WINGS AND LEGS OF DUCKS AND FOWLS.

The reduced wings and enlarged legs of domesticated ducks and fowls are
attributed by Darwin and Spencer to the inheritance of the effects of
use and disuse. But the inference by no means follows. Natural selection
would usually favour these adaptive changes, and they would also have
been aided by an artificial selection which is often unconscious or
indirect. Birds with diminished power of flight would be less difficult
to keep and manage, and in preserving and multiplying such birds man
would be unconsciously bringing about structural changes which would
easily be regarded as effects of use and disuse. "About eighteen
centuries ago Columella and Varro speak of the necessity of keeping
ducks in netted enclosures like other wild fowl, so that at this period
there was danger of their flying away."[22] Is it not probable that the
best fliers would escape most frequently, or would pine most if kept
confined? On the other hand, birds with lessened powers of flight would
not be eliminated as under natural conditions, but would be favoured;
and natural selection, together with artificial selection of the most
flourishing birds, would thicken and strengthen the legs to meet
increased demands upon t