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The Descent of Man and Selection in Relation to Sex

Secondary Sexual Characters Of Mammals--continued.
Voice--Remarkable sexual peculiarities in seals--Odour--Development of the hair--
Colour of the hair and skin--Anomalous case of the female being more ornamented than
the male--Colour and ornaments due to sexual selection-- Colour acquired for the sake of
protection--Colour, though common to both sexes, often due to sexual selection--On the
disappearance of spots and stripes in adult quadrupeds--On the colours and ornaments of
the Quadrumana--Summary.
Quadrupeds use their voices for various purposes, as a signal of danger, as a call from
one member of a troop to another, or from the mother to her lost offspring, or from the
latter for protection to their mother; but such uses need not here be considered. We are
concerned only with the difference between the voices of the sexes, for instance between
that of the lion and lioness, or of the bull and cow. Almost all male animals use their
voices much more during the rutting-season than at any other time; and some, as the
giraffe and porcupine (1. Owen, 'Anatomy of Vertebrates,' vol. iii. p. 585.), are said to be
completely mute excepting at this season. As the throats (i.e. the larynx and thyroid
bodies (2. Ibid. p. 595.)) of stags periodically become enlarged at the beginning of the
breeding-season, it might be thought that their powerful voices must be somehow of high
importance to them; but this is very doubtful. From information given to me by two
experienced observers, Mr. McNeill and Sir P. Egerton, it seems that young stags under
three years old do not roar or bellow; and that the old ones begin bellowing at the
commencement of the breeding-season, at first only occasionally and moderately, whilst
they restlessly wander about in search of the females. Their battles are prefaced by loud
and prolonged bellowing, but during the actual conflict they are silent. Animals of all
kinds which habitually use their voices utter various noises under any strong emotion, as
when enraged and preparing to fight; but this may merely be the result of nervous
excitement, which leads to the spasmodic contraction of almost all the muscles of the
body, as when a man grinds his teeth and clenches his fists in rage or agony. No doubt
stags challenge each other to mortal combat by bellowing; but those with the more
powerful voices, unless at the same time the stronger, better-armed, and more
courageous, would not gain any advantage over their rivals.
It is possible that the roaring of the lion may be of some service to him by striking terror
into his adversary; for when enraged he likewise erects his mane and thus instinctively
tries to make himself appear as terrible as possible. But it can hardly be supposed that the
bellowing of the stag, even if it be of service to him in this way, can have been important
enough to have led to the periodical enlargement of the throat. Some writers suggest that
the bellowing serves as a call to the female; but the experienced observers above quoted
inform me that female deer do not search for the male, though the males search eagerly
for the females, as indeed might be expected from what we know of the habits of other
male quadrupeds. The voice of the female, on the other hand, quickly brings to her one or
more stags (3. See, for instance, Major W. Ross King ('The Sportsman in Canada,' 1866,
pp. 53, 131) on the habits of the moose and wild reindeer.), as is well known to the
hunters who in wild countries imitate her cry. If we could believe that the male had the
power to excite or allure the female by his voice, the periodical enlargement of his vocal
organs would be intelligible on the principle of sexual selection, together with inheritance
limited to the same sex and season; but we have no evidence in favour of this view. As
the case stands, the loud voice of the stag during the breeding-season does not seem to be