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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2932 times)
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« Reply #180 on: February 10, 2009, 01:24:50 pm »

* The Variation of Animals and Plants under Domestication, 1868,
vol. i., pp. 61-64.
  *(2) Proc. Zool. Soc., 1862, p. 164. See, also, Dr. Hartmann, Ann.
d. Landw., Dd. xliii., s. 222.

  Quadrumana.- Before we conclude, it will be well to add a few
remarks on the ornaments of monkeys. In most of the species the
sexes resemble each other in colour, but in some, as we have seen, the
males differ from the females, especially in the colour of the naked
parts of the skin, in the development of the beard, whiskers, and
mane. Many species are coloured either in so extraordinary or so
beautiful a manner, and are furnished with such curious and elegant
crests of hair, that we can hardly avoid looking at these characters
as having been gained for the sake of ornament. The accompanying
figures (see figs. 72 to 76) serve to shew the arrangement of the hair
on the face and head in several species. It is scarcely conceivable
that these crests of hair, and the strongly contrasted colours of
the fur and skin, can be the result of mere variability without the
aid of selection; and it is inconceivable that they can be of use in
any ordinary way to these animals. If so, they have probably been
gained through sexual selection, though transmitted equally, or almost
equally, to both sexes. With many of the Quadrumana, we have
additional evidence of the action of sexual selection in the greater
size and strength of the males, and in the greater development of
their canine teeth, in comparison with the females.
  A few instances will suffice of the strange manner in which both
sexes of some species are coloured, and of the beauty of others. The
face of the Cercopithecus petaurista (see fig. 77) is black, the
whiskers and beard being white, with a defined, round, white spot on
the nose, covered with short white hair, which gives to the animal
an almost ludicrous aspect. The Semnopithecus frontatus likewise has a
blackish face with a long black beard, and a large naked spot on the
forehead of a bluish-white colour. The face of Macacus lasiotus is
dirty flesh-coloured, with a defined red spot on each cheek. The
appearance of Cercocebus aethiops is grotesque, with its black face,
white whiskers and collar, chestnut head, and a large naked white spot
over each eyelid. In very many species, the beard, whiskers, and
crests of hair round the face are of a different colour from the
rest of the head, and when different, are always of a lighter tint,*
being often pure white, sometimes bright yellow, or reddish. The whole
face of the South American Brachyurus calvus is of a "glowing
scarlet hue"; but this colour does not appear until the animal is
nearly mature.*(2) The naked skin of the face differs wonderfully in
colour in the various species. It is often brown or flesh-colour, with
parts perfectly white, and often as black as that of the most sooty
negro. In the Brachyurus the scarlet tint is brighter than that of the
most blushing Caucasian damsel. It is sometimes more distinctly orange
than in any Mongolian, and in several species it is blue, passing into
violet or grey. In all the species known to Mr. Bartlett, in which the
adults of both sexes have strongly-coloured faces, the colours are
dull or absent during early youth. This likewise holds good with the
mandrill and Rhesus, in which the face and the posterior parts of
the body are brilliantly coloured in one sex alone. In these latter
cases we have reason to believe that the colours were acquired through
sexual selection; and we are naturally led to extend the same view
to the foregoing species, though both sexes when adult have their
faces coloured in the same manner.

  * I observed this fact in the Zoological Gardens; and many cases may
be seen in the coloured plates in Geoffroy St-Hilaire and F. Cuvier,
Histoire Nat. des Mammiferes, tom. i., 1824.
  *(2) Bates, The Naturalist on the Amazons, 1863, vol. ii., p. 310.

  Although many kinds of monkeys are far from beautiful according to
our taste, other species are universally admired for their elegant
appearance and bright colours. The Semnopithecus nemaeus, though
peculiarly coloured, is described as extremely pretty; the
orange-tinted face is surrounded by long whiskers of glossy whiteness,
with a line of chestnut-red over the eyebrows; the fur on the back
is of a delicate grey, with a square patch on the loins, the tail
and the fore-arms being of a pure white; a gorget of chestnut
surmounts the chest; the thighs are black, with the legs chestnut-red.
I will mention only two other monkeys for their beauty; and I have
selected these as presenting slight sexual differences in colour,
which renders it in some degree probable that both sexes owe their
elegant appearance to sexual selection. In the moustache-monkey
(Cercopithecus cephus) the general colour of the fur is
mottled-greenish with the throat white; in the male the end of the
tail is chestnut, but the face is the most ornamented part, the skin
being chiefly bluish-grey, shading into a blackish tint beneath the
eyes, with the upper lip of a delicate blue, clothed on the lower edge
with a thin black moustache; the whiskers are orange-coloured, with
the upper part black, forming a band which extends backwards to the
ears, the latter being clothed with whitish hairs. In the Zoological
Society's Gardens I have often overheard visitors admiring the
beauty of another monkey, deservedly called Cercopithecus diana (see
fig. 78); the general colour of the fur is grey; the chest and inner
surface of the fore legs are white; a large triangular defined space
on the hinder part of the back is rich chestnut; in the male the inner
sides of the thighs and the abdomen are delicate fawn-coloured, and
the top of the head is black; the face and ears are intensely black,
contrasting finely with a white transverse crest over the eyebrows and
a long white peaked beard, of which the basal portion is black.*

  * I have seen most of the above monkeys in the Zoological
Society's Gardens. The description of the Semnopithecus nemaeus is
taken from Mr. W. C. Martin's Natural History of Mammalia, 1841, p.
460; see also pp. 475, 523.

 In these and many other monkeys, the beauty and singular
arrangement of their colours, and still more the diversified and
elegant arrangement of the crests and tufts of hair on their heads,
force the conviction on my mind that these characters have been
acquired through sexual selection exclusively as ornaments.

  Summary.- The law of battle for the possession of the female appears
to prevail throughout the whole great class of mammals. Most
naturalists will admit that the greater size, strength, courage, and
pugnacity of the male, his special weapons of offence, as well as
his special means of defence, have been acquired or modified through
that form of selection which I have called sexual. This does not
depend on any superiority in the general struggle for life, but on
certain individuals of one sex, generally the male, being successful
in conquering other males, and leaving a larger number of offspring to
inherit their superiority than do the less successful males.
  There is another and more peaceful kind of contest, in which the
males endeavour to excite or allure the females by various charms.
This is probably carried on in some cases by the powerful odours
emitted by the males during the breeding-season; the odoriferous
glands having been acquired through sexual selection. Whether the same
view can be extended to the voice is doubtful, for the vocal organs of
the males must have been strengthened by use during maturity, under
the powerful excitements of love, jealousy or rage, and will
consequently have been transmitted to the same sex. Various crests,
tufts, and mantles of hair, which are either confined to the male,
or are more developed in this sex than in the female, seem in most
cases to be merely ornamental, though they sometimes serve as a
defence against rival males. There is even reason to suspect that
the branching horns of stags, and the elegant horns of certain
antelopes, though properly serving as weapons of offence or defence,
have been partly modified for ornament.
  When the male differs in colour from the female, he generally
exhibits darker and more strongly-contrasted tints. We do not in
this class meet with the splendid red, blue, yellow, and green
tints, so common with male birds and many other animals. The naked
parts, however, of certain Quadrumana must be excepted; for such
parts, often oddly situated, are brilliantly coloured in some species.
The colours of the male in other cases may be due to simple variation,
without the aid of selection. But when the colours are diversified and
strongly pronounced, when they are not developed until near
maturity, and when they are lost after emasculation, we can hardly
avoid the conclusion that they have been acquired through sexual
selection for the sake of ornament, and have been transmitted
exclusively, or almost exclusively, to the same sex. When both sexes
are coloured in the same manner, and the colours are conspicuous or
curiously arranged, without being of the least apparent use as a
protection, and especially when they are associated with various other
ornamental appendages, we are led by analogy to the same conclusion,
namely, that they have been acquired through sexual selection,
although transmitted to both sexes. That conspicuous and diversified
colours, whether confined to the males or common to both sexes, are as
a general rule associated in the same groups and sub-groups with other
secondary sexual characters serving for war or for ornament, will be
found to hold good, if we look back to the various cases given in this
and the last chapter.
  The law of the equal transmission of characters to both sexes, as
far as colour and other ornaments are concerned, has prevailed far
more extensively with mammals than with birds; but weapons, such as
horns and tusks, have often been transmitted either exclusively or
much more perfectly to the males than to the females. This is
surprising, for, as the males generally use their weapons for
defence against enemies of all kinds, their weapons would have been of
service to the females. As far as we can see, their absence in this
sex can be accounted for only by the form of inheritance which has
prevailed. Finally, with quadrupeds the contest between the
individuals of the same sex, whether peaceful or bloody, has, with the
rarest exceptions, been confined to the males; so that the latter have
been modified through sexual selection, far more commonly than the
females, either for fighting with each other or for alluring the
opposite sex.

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