been most protected from the heat of the sun. The crown of the head,
however, offers a curious exception, for at all times it must have been
one of the most exposed parts, yet it is thickly clothed with hair. The
fact, however, that the other members of the order of Primates, to
which man belongs, although inhabiting various hot regions, are well
clothed with hair, generally thickest on the upper surface (88. Isidore
Geoffroy St.-Hilaire remarks ( Histoire Nat. Generale, tom. ii. 1859,
pp. 215-217) on the head of man being covered with long hair; also on
the upper surfaces of monkeys and of other mammals being more thickly
clothed than the lower surfaces. This has likewise been observed by
various authors. Prof. P. Gervais ( Histoire Nat. des Mammiferes, tom.
i. 1854, p. 28), however, states that in the Gorilla the hair is
thinner on the back, where it is partly rubbed off, than on the lower
surface.), is opposed to the supposition that man became naked through
the action of the sun. Mr. Belt believes (89. The Naturalist in
Nicaragua, 1874, p. 209. As some confirmation of Mr. Belt s view, I
may quote the following passage from Sir W. Denison ( Varieties of
Vice-Regal Life, vol. i. 1870, p. 440): It is said to be a practice
with the Australians, when the vermin get troublesome, to singe
themselves. ) that within the tropics it is an advantage to man to be
destitute of hair, as he is thus enabled to free himself of the
multitude of ticks (acari) and other parasites, with which he is often
infested, and which sometimes cause ulceration. But whether this evil
is of sufficient magnitude to have led to the denudation of his body
through natural selection, may be doubted, since none of the many
quadrupeds inhabiting the tropics have, as far as I know, acquired any
specialised means of relief. The view which seems to me the most
probable is that man, or rather primarily woman, became divested of
hair for ornamental purposes, as we shall see under Sexual Selection;
and, according to this belief, it is not surprising that man should
differ so greatly in hairiness from all other Primates, for characters,
gained through sexual selection, often differ to an extraordinary
degree in closely related forms.
According to a popular impression, the absence of a tail is eminently
distinctive of man; but as those apes which come nearest to him are
destitute of this organ, its disappearance does not relate exclusively
to man. The tail often differs remarkably in length within the same
genus: thus in some species of Macacus it is longer than the whole
body, and is formed of twenty-four vertebrae; in others it consists of
68