ardly suppose that disuse would maintain
or develop the projecting chin, increase its perpendicular height till
the jaw is deepest and strongest at its extremity, evolve a side flange,
and enlarge the upper jaw-bone to form part of a more prominent nose,
while drawing back the savagely obtrusive teeth and lips to a more
pleasing and subdued position of retirement and of humanized beauty. If
human preference and natural selection caused some of these differences,
why are they incompetent to effect changes in the direction of a
diminution of the jaw or teeth? And if use and disuse are the sole
modifying agents in the case of the human jaw, why should men have any
more chin than a gorilla or a dog?

The excessive weight of the West African jaws at the College of Surgeons
is partly _against_ Mr. Spencer's contention, unless he assumes that
Guinea Negroes use their jaws far more than the Australians, a
supposition which seems extremely improbable. The heavier skull and
narrower molar teeth point however to other factors than increased use.

The striking variability of the human jaw is strongly opposed to the
idea of its being under the direct and dominant control of so uniform a
cause as ancestral use and disuse. Mr. Spencer regards a variation of 1
oz. as a large one, but I found that the English jaws in the College of
Surgeons varied from 1.9 oz. to 4.3 oz. (or 5 oz. if lost teeth were
allowed for); Australian jaws varied from 2 oz. to 4.5 oz. (with _no_
lost teeth to allow for); while in Negro jaws the maximum rose to over
5-1/2 oz.[4] In spite of disuse some European jaws were twice as heavy
as the lightest Australian jaw, either absolutely or (in some cases)
relatively to the cranium. The uniformity of change relied upon by Mr.
Spencer is scarcely borne out by the facts so far as male jaws are
concerned. The great reduction in the weight of _female_ jaws _and
skulls_ evidently points to sexual selection and to panmixia under male
protection.

I think, on the whole, we must conclude that the human jaws do not
afford satisfactory proof of the inheritance of the effects of use and
disuse, inasmuch as the differences in their weight and shape and size
can be more reasonably and consistently accounted for as the result of
less disputable causes.

DIMINISHED BITING MUSCLES OF LAP-DOGS.

The next example, the reduced biting muscles, &c., of lap-dogs is also
unsatisfactory as a proof of the inheritance of the effects of