the United States Commission (22. Investigations, etc., by B.A.
Gould, 1869, p. 288.) that the legs of the sailors employed in the late
war were longer by 0.217 of an inch than those of the soldiers, though
the sailors were on an average shorter men; whilst their arms were
shorter by 1.09 of an inch, and therefore, out of proportion, shorter
in relation to their lesser height. This shortness of the arms is
apparently due to their greater use, and is an unexpected result: but
sailors chiefly use their arms in pulling, and not in supporting
weights. With sailors, the girth of the neck and the depth of the
instep are greater, whilst the circumference of the chest, waist, and
hips is less, than in soldiers.
Whether the several foregoing modifications would become hereditary, if
the same habits of life were followed during many generations, is not
known, but it is probable. Rengger (23. Saugethiere von Paraguay,
1830, s. 4.) attributes the thin legs and thick arms of the Payaguas
Indians to successive generations having passed nearly their whole
lives in canoes, with their lower extremities motionless. Other writers
have come to a similar conclusion in analogous cases. According to
Cranz (24. History of Greenland, Eng. translat., 1767, vol. i. p.
230.), who lived for a long time with the Esquimaux, the natives
believe that ingenuity and dexterity in seal-catching (their highest
art and virtue) is hereditary; there is really something in it, for the
son of a celebrated seal-catcher will distinguish himself, though he
lost his father in childhood. But in this case it is mental aptitude,
quite as much as bodily structure, which appears to be inherited. It is
asserted that the hands of English labourers are at birth larger than
those of the gentry. (25. Intermarriage, by Alex. Walker, 1838, p.
377.) From the correlation which exists, at least in some cases (26.
The Variation of Animals under Domestication, vol. i. p. 173.),
between the development of the extremities and of the jaws, it is
possible that in those classes which do not labour much with their
hands and feet, the jaws would be reduced in size from this cause. That
they are generally smaller in refined and civilised men than in
hard-working men or savages, is certain. But with savages, as Mr.
Herbert Spencer (27. Principles of Biology, vol. i. p. 455.) has
remarked, the greater use of the jaws in chewing coarse, uncooked food,
would act in a direct manner on the masticatory muscles, and on the
bones to which they are attached. In infants, long before birth, the
skin on the soles of the feet is thicker than on any other part of the
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