Chapter XVIII - Secondary Sexual Characters of Mammals- Continued

  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,* are said to be completely mute excepting at this season.
As the throats (i.e. the larynx and thyroid bodies*(2)) 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.

  * Owen, Anatomy of Vertebrates, vol. iii., p. 585.
  *(2) Ibid., p. 595.

  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,* 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 of any special service to him, either during his
courtship or battles, or in any other way. But may we not believe that
the frequent use of the voice, under the strong excitement of love,
jealousy, and rage, continued during many generations, may at last
have produced an inherited effect on the vocal organs of the stag,
as well as of other male animals;, This appears to me, in our
present state of knowledge, the most probable view.

  * See, for instance, Major W. Ross King (The Sportsman in Canada,
1866, pp. 53, 131) on the habits of the moose and wild reindeer.

  The voice of the adult male gorilla is tremendous, and he is
furnished with a laryngeal sack, as is the adult male orang.* The
gibbons rank among the noisiest of monkeys, and the Sumatra species
(Hylobates syndactylus) is also furnished with an air sack; but Mr.
Blyth, who has had opportunities for observation, does not believe
that the male is noisier than the female. Hence, these latter
monkeys probably use their voices as a mutual call; and this is
certainly the case with some quadrupeds, for instance the
beaver.*(2) Another gibbon, the H. agilis, is remarkable, from
having the power of giving a complete and correct octave of musical
notes,*(3) which we may reasonably suspect serves as a sexual charm;
but I shall have to recur to this subject in the next chapter. The
vocal organs of the American Mycetes caraya are one-third larger in
the male than in the female, and are wonderfully powerful. These
monkeys in warm weather make the forests resound at morning and
evening with their overwhelming voices. The males begin the dreadful
concert, and often continue it during many hours, the females
sometimes joining in with their less powerful voices. An excellent
observer, Rengger,*(4) could not perceive that they were excited to
begin by any special cause; he thinks that, like many birds, they
delight in their own music, and try to excel each other. Whether
most of the foregoing monkeys have acquired their powerful voices in
order to beat their rivals and charm the females- or whether the vocal
organs have been strengthened and enlarged through the inherited
effects of long-continued use without any particular good being thus
gained- I will not pretend to say; but the former view, at least in
the case of the Hylobates agilis, seems the most probable.

  * Owen Anatomy of Vertebrates, vol. iii., p. 600.
  *(2) Mr. Green, in Journal of Linnean Society, vol. x., Zoology,
1869, note 362.
  *(3) C. L. Martin, General Introduction to the Natural History of
Mamm. Animals, 1841, p. 431.
  *(4) Naturgeschichte der Saugethiere von Paraguay, 1830, ss. 15, 21.

  I may here mention two very curious sexual peculiarities occurring
in seals, because they have been supposed by some writers to affect
the voice. The nose of the male sea-elephant (Macrorhinus
proboscideus) becomes greatly elongated during the breeding-season,
and can then be erected. In this state it is sometimes a foot in
length. The female is not thus provided at any period of life. The
male makes a wild, hoarse, gurgling noise, which is audible at a great
distance and is believed to be strengthened by the proboscis; the
voice of the female being different. Lesson compares the erection of
the proboscis, with the swelling of the wattles of male gallinaceous
birds whilst courting the females. In another allied kind of seal, the
bladder-nose (Cystophora cristata), the head is covered by a great
hood or bladder. This supported by the septum of the nose, which is
produced far backwards and rises into an internal crest seven inches
in height. The hood is clothed with short hair, and is muscular; can
be inflated until it more than equals the whole head in size! The
males when rutting, fight furiously on the ice, and their roaring
"is said to be sometimes so loud as to be heard four miles off."
When attacked they likewise roar or bellow; and whenever irritated the
bladder is inflated and quivers. Some naturalists believe that the
voice is thus strengthened, but various other uses have been
assigned to this extraordinary structure. Mr. R. Brown thinks that
it serves as a protection against accidents of all kinds; but this
is not probable, for, as I am assured by Mr. Lamont who killed 600
of these animals, the hood is rudimentary in the females, and it is
not developed in the males during youth.*

  * On the sea-elephant, see an article by Lesson, in Dict. Class.
Hist. Nat., tom. xiii., p. 418. For the Cystophora, or Stemmatopus,
see Dr. Dekay, Annals of Lyceum of Nat. Hist., New York, vol. i.,
1824, p. 94. Pennant has also collected information from the sealers
on this animal. The fullest account is given by Mr. Brown, in Proc.
Zoolog. Soc., 1868, p. 435.

  Odour.- With some animals, as with the notorious skunk of America,
the overwhelming odour which they emit appears to serve exclusively as
a defence. With shrew-mice (Sorex) both sexes possess abdominal
scent-glands and there can be little doubt, from the rejection of
their bodies by birds and beasts of prey, that the odour is
protective; nevertheless, the glands become enlarged in the males
during the breeding-season. In many other quadrupeds the glands are of
the same size in both sexes,* but their uses are not known. In other
species the glands are confined to the males, or are more developed
than in the females; and they almost always become more active
during the rutting-season. At this period the glands on the sides of
the face of the male elephant enlarge, and emit a secretion having a
strong musky odour. The males, and rarely the females, of many kinds
of bats have glands and protrudable sacks situated in various parts;
and it is believed that these are odoriferous.

  * As with the castoreum of the beaver, see Mr. L. H. Morgan's most
interesting work, The American Beaver, 1868, p. 300. Pallas (Spic.
Zoolog., fasc. viii., 1779, p. 23) has well discussed the
odoriferous glands of mammals. Owen (Anat. of Vertebrates, vol.
iii., p. 634) also gives an account of these glands, including those
of the elephant, and (p. 763) those of shrew-mice. On bats, Mr.
Dobson, Proceedings of the Zoological Society. 1873, p. 241.

  The rank effluvium of the male goat is well known, and that of
certain male deer is wonderfully strong and persistent. On the banks
of the Plata I perceived the air tainted with the odour of the male
Cervus campestris, at half a mile to leeward of a herd; and a silk
handkerchief, in which I carried home a skin, though often used and
washed, retained, when first unfolded, traces of the odour for one
year and seven months. This animal does not emit its strong odour
until more than a year old, and if castrated whilst young never
emits it.* Besides the general odour, permeating the whole body of
certain ruminants (for instance Bos moschatus) in the breeding-season,
many deer, antelopes, sheep, and goats possess odoriferous glands in
various situations, more especially on their faces. The so-called
tear-sacks, or suborbital pits, come under this head. These glands
secrete a semi-fluid fetid matter which is sometimes so copious as
to stain the whole face, as I have myself seen in an antelope. They
are "usually larger in the male than in the female, and their
development is checked by castration."*(2) According to Desmarest they
are altogether absent in the female of Antilope subgutturosa. Hence,
there can be no doubt that they stand in close relation with the
reproductive functions. They are also sometimes present, and sometimes
absent, in nearly allied forms. In the adult male musk-deer (Moschus
moschiferus), a naked space round the tail is bedewed with an
odoriferous fluid, whilst in the adult female, and in the male until
two years old, this space is covered with hair and is not odoriferous.
The proper musk-sack of this deer is from its position necessarily
confined to the male, and forms an additional scent-organ. It is a
singular fact that the matter secreted by this latter gland, does not,
according to Pallas, change in consistence, or increase in quantity,
during the rutting-season; nevertheless this naturalist admits that
its presence is in some way connected with the act of reproduction. He
gives, however, only a conjectural and unsatisfactory explanation of
its use.*(3)

  * Rengger, Naturgeschichte der Saugethiere von Paraguay, 1830, s.
355. This observer also gives some curious particulars in regard to
the odour.
  *(2) Owen, Anatomy of Vertebrates, vol. iii., p. 632. See also Dr.
Murie's observations on those glands in the Proc. Zoolog. Soc.,
1870, p. 340. Desmarest, "On the Antilope subgutturosa," Mammalogie,
1820, p. 455.
  *(3) Pallas, Spicilegia Zoolog., fasc. xiii., 1779, p. 24;
Desmoulins, Dict. Class. d'Hist. Nat., tom. iii., p. 586.

  In most cases, when only the male emits a strong odour during the
breeding-season, it probably serves to excite or allure the female. We
must not judge on this head by our own taste, for it is well known
that rats are enticed by certain essential oils, and cats by valerian,
substances far from agreeable to us; and that dogs, though they will
not eat carrion, sniff and roll on it. From the reasons given when
discussing the voice of the stag, we may reject the idea that the
odour serves to bring the females from a distance to the males. Active
and long-continued use cannot here have come into play, as in the case
of the vocal organs. The odour emitted must be of considerable
importance to the male, inasmuch as large and complex glands,
furnished with muscles for everting the sack, and for closing or
opening the orifice, have in some cases been developed. The
development of these organs is intelligible through sexual
selection, if the most odoriferous males are the most successful in
winning the females, and in leaving offspring to inherit their
gradually perfected glands and odours.
  Development of the Hair.- We have seen that male quadrupeds often
have the hair on their necks and shoulders much more developed than
the females; and many additional instances could be given. This
sometimes serves as a defence to the male during his battles; but
whether the hair in most cases has been specially developed for this
purpose, is very doubtful. We may feel almost certain that this is not
the case, when only a thin and narrow crest runs along the back; for a
crest of this kind would afford scarcely any protection, and the ridge
of the back is not a place likely to be injured; nevertheless such
crests are sometimes confined to the males, or are much more developed
in them than in the females. Two antelopes, the Tragelaphus
scriptus* (see fig. 70) and Portax picta may be given as instances.
When stags, and the males of the wild goat, are enraged or
terrified, these crests stand erect;*(2) but it cannot be supposed
that they have been developed merely for the sake of exciting fear
in their enemies. One of the above-named antelopes, the Portax
picta, has a large well-defined brush of black hair on the throat, and
this is much larger in the male than in the female. In the
Ammotragus tragelaphus of north Africa, a member of the
sheep-family, the fore-legs are almost concealed by an extraordinary
growth of hair, which depends from the neck and upper halves of the
legs; but Mr. Bartlett does not believe that this mantle is of the
least use to the male, in whom it is much more developed than in the
female.

  * Dr. Gray, Gleanings from the Menagerie at Knowsley, pl. 28.
  *(2) Judge Caton on the wapiti, Transact. Ottawa Acad. Nat.
Sciences, 1868, pp. 36, 40; Blyth, Land and Water, on Capra aegagrus
1867, p. 37.

 Male quadrupeds of many kinds differ from the females in having
more hair, or hair of a different character, on certain parts of their
faces. Thus the bull alone has curled hair on the forehead.* In
three closely-allied
sub-genera of the goat family, only the males possess beards sometimes
of large size; in two other sub-genera both sexes have a beard, but it
disappears in some of the domestic breeds of the common goat; and
neither sex of the Hemitragus has a beard. In the ibex the beard is
not developed during the summer, and it is so small at other times
that it may be called rudimentary.*(2) With some monkeys the beard
is confined to the male, as in the orang; or is much larger in the
male than in the female, as in the Mycetes caraya and Pithecia satanas
(see fig. 68). So it is with the whiskers of some species of
Macacus,*(3) and, as we have seen, with the manes of some species of
baboons. But with most kinds of monkeys the various tufts of hair
about the face and head are alike in both sexes.

  * Hunter's Essays and Observations, edited by Owen, 1861. vol. i.,
p. 236.
  *(2) See Dr. Gray's Catalogue of Mammalia in the British Museum,
part iii., 1852, p. 144.
  *(3) Rengger, Saugthiere, &c., s. 14; Desmarest, Mammalogie, p. 86.

  The males of various members of the ox family (Bovidae), and of
certain antelopes, are furnished with a dewlap, or great fold of
skin on the neck, which is much less developed in the female.
  Now, what must we conclude with respect to such sexual differences
as these? No one will pretend that the beards of certain male goats,
or the dewlaps of the bull, or the crests of hair along the backs of
certain male antelopes, are of any use to them in their ordinary
habits. It is possible that the immense beard of the male Pithecia,
and the large beard of the male orang, may protect their throats
when fighting; for the keepers in the Zoological Gardens inform me
that many monkeys attack each other by the throat; but it is not
probable that the beard has been developed for a distinct purpose from
that served by the whiskers, moustache, and other tufts of hair on the
face; and no one will suppose that these are useful as a protection.
Must we attribute all these appendages of hair or skin to mere
purposeless variability in the male? It cannot be denied that this
is possible; for in many domesticated quadrupeds, certain
characters, apparently not derived through reversion from any wild
parent form, are confined to the males, or are more developed in
them than in the females- for instance, the hump on the male
zebu-cattle of India, the tail of fat-tailed rams, the arched
outline of the forehead in the males of several breeds of sheep, and
lastly, the mane, the long hairs on the hind legs, and the dewlap of
the male of the Berbura goat.* The mane, which occurs only in the rams
of an African breed of sheep, is a true secondary sexual character,
for, as I hear from Mr. Winwood Reade, it is not developed if the
animal be castrated. Although we ought to be extremely cautious, as
shewn in my work on Variation under Domestication, in concluding
that any character, even with animals kept by semi-civilised people,
has not been subjected to selection by man, and thus augmented, yet in
the cases just specified this is improbable; more especially as the
characters are confined to the males, or are more strongly developed
in them than in the females. If it were positively known that the
above African ram is a descendant of the same primitive stock as the
other breeds of sheep, and if the Berbura male-goat with his mane,
dewlap, &c., is descended from the same stock as other goats, then,
assuming that selection has not been applied to these characters, they
must be due to simple variability, together with sexually-limited
inheritance.

  * See the chapters on these several animals in vol. i. of my
Variation of Animals under Domestication; also vol. ii., p. 73; also
chap. xx. on the practice of selection by semi-civilised people. For
the Berbuar goat, see Dr. Gray, Catalogue, ibid., p. 157.

  Hence it appears reasonable to extend this same view to all
analogous cases with animals in a state of nature. Nevertheless I
cannot persuade myself that it generally holds good, as in the case of
the extraordinary development of hair on the throat and fore-legs of
the male Ammotragus, or in that of the immense beard of the male
Pithecia. Such study as I have been able to give to nature makes me
believe that parts or organs which are highly developed, were acquired
at some period for a special purpose. With those antelopes in which
the adult male is more strongly-coloured than the female, and with
those monkeys in which the hair on the face is elegantly arranged
and coloured in a diversified manner, it seems probable that the
crests and tufts of hair were gained as ornaments; and this I know
is the opinion of some naturalists. If this be correct, there can be
little doubt that they were gained or at least modified through sexual
selection; but how far the same view may be extended to other
mammals is doubtful.

  Colour of the Hair and of the Naked Skin.- I will first give briefly
all the cases known to me of male quadrupeds differing in colour
from the females. With marsupials, as I am informed by Mr. Gould,
the sexes rarely differ in this respect; but the great red kangaroo
offers a striking exception, "delicate blue being the prevailing
tint in those parts of the female which in the male are red."* In
the Didelphis opossum of Cayenne the female is said to be a little
more red than the male. Of the rodents, Dr. Gray remarks: "African
squirrels, especially those found in the tropical regions, have the
fur much brighter and more vivid at some seasons of the year than at
others, and the fur of the male is generally brighter than that of the
female."*(2) Dr. Gray informs me that he specified the African
squirrels, because, from their unusually bright colours, they best
exhibit this difference. The female of the Mus minutus of Russia is of
a paler and dirtier tint than the male. In a large number of bats
the fur of the male is lighter than in the female.*(3) Mr. Dobson also
remarks, with respect to these animals: "Differences, depending partly
or entirely on the possession by the male of fur of a much more
brilliant hue, or distinguished by different markings or by the
greater length of certain portions, are met only, to any appreciable
extent, in the frugivorous bats in which the sense of sight is well
developed." This last remark deserves attention, as bearing on the
question whether bright colours are serviceable to male animals from
being ornamental. In one genus of sloths, it is now established, as
Dr. Gray states, "that the males are ornamented differently from the
females- that is to say, that they have a patch of soft short hair
between the shoulders, which is generally of a more or less orange
colour, and in one species pure white. The females, on the contrary,
are destitute of this mark."

  * Osphranter rufus, Gould, Mammals of Australia, 1863, vol. ii. On
the Didelphis, Desmarest, Mammalogie, p. 256.
  *(2) Annals and Magazine of Natural History, Nov., 1867, p. 325.
On the Mus minutus, Desmarest, Mammalogie, p. 304.
  *(3) J. A. Allen, in Bulletin of Mus. Comp. Zoolog. of Cambridge,
United States, 1869, p. 207. Mr. Dobson on sexual characters in the
Chiroptera, Proceedings of the Zoological Society, 1873, p. 241. Dr.
Gray on sloths, ibid., 1871, p. 436.

  The terrestrial Carnivora and Insectivora rarely exhibit sexual
differences of any kind, including colour. The ocelot (Felis
pardalis), however, is exceptional, for the colours of the female,
compared with those of the male, are "moins apparentes, le fauve,
etant plus terne, le blanc moins pur, les raies ayant moins de largeur
et les taches moins de diametre."* The sexes of the allied Felis mitis
also differ, but in a less degree; the general hues of the female
being rather paler than in the male, with the spots less black. The
marine Carnivora or seals, on the other hand, sometimes differ
considerably in colour, and they present, as we have already seen,
other remarkable sexual differences. Thus the male of the Otaria
nigrescens of the southern hemisphere is of a rich brown shade
above; whilst the female, who acquires her adult tints earlier in life
than the male, is dark-grey above, the young of both sexes being of
a deep chocolate colour. The male of the northern Phoca groenlandica
is tawny grey, with a curious saddle-shaped dark mark on the back; the
female is much smaller, and has a very different appearance, being
"dull white or yellowish straw-colour, with a tawny hue on the
back"; the young at first are pure white, and can "hardly be
distinguished among the icy hummocks and snow, their colour thus
acting as a protection."*(2)

  * Desmarest Mammalogie, 1820, p. 220. On Felis mitis, Rengger,
ibid., s. 194.
  *(2) Dr. Murie on the Otaria, Proceedings Zoological Society,
1869, p. 108. Mr. R. Brown on the P. groenlandica, ibid., 1868, p.
417. See also on the colours of seals, Desmarest, ibid., pp. 243, 249.

  With ruminants sexual differences of colour occur more commonly than
in any other order. A difference of this kind is general in the
strepsicerene antelopes; thus the male nilghau (Portax picta) is
bluish-grey and much darker than the female, with the square white
patch on the throat, the white marks on the fetlocks, and the black
spots on the ears all much more distinct. We have seen that in this
species the crests and tufts of hair are likewise more developed in
the male than in the hornless female. I am informed by Mr. Blyth
that the male, without shedding his hair, periodically becomes
darker during the breeding-season. Young males cannot be distinguished
from young females until about twelve months old; and if the male is
emasculated before this period, he never, according to the same
authority, changes colour. The importance of this latter fact, as
evidence that the colouring of the Portax is of sexual origin, becomes
obvious, when we hear* that neither the red summer coat nor the blue
winter-coat of the Virginian deer is at all affected by
emasculation. With most or all of the highly-ornamented species of
Tragelaphus the males are darker than the hornless females, and
their crests of hair are more fully developed. In the male of that
magnificent antelope, the Derbyan eland, the body is redder, the whole
neck much blacker, and the white band which separates these colours
broader than in the female. In the Cape eland, also, the male is
slightly darker than the female.*(2)

  * Judge Caton, in Transactions of the Ottawa Academy of Natural
Sciences, 1868, p. 4.
  *(2) Dr. Gray, Cat. of Mamm. in Brit. Mus., part iii., 1852, pp.
134-142; also Dr. Gray, Gleanings from the Menagerie of Knowsley, in
which there is a splendid drawing of the Oreas derbianus: see the text
on Tragelaphus. For the Cape eland (Oreas canna), see Andrew Smith,
Zoology of S. Africa, pls. 41 and 42. There are also many of these
antelopes in the Zoological Gardens.

  In the Indian black-buck (A. bezoartica), which belongs to another
tribe of antelopes, the male is very dark, almost black; whilst the
hornless female is fawn-coloured. We meet in this species, as Mr.
Blyth informs me, with an exactly similar series of facts, as in the
Portax picta, namely, in the male periodically changing colour
during the breeding-season, in the effects of emasculation on this
change, and in the young of both sexes being indistinguishable from
each other. In the Antilope niger the male is black, the female, as
well as the young of both sexes, being brown; in A. sing-sing the male
is much brighter coloured than the hornless female, and his chest
and belly are blacker; in the male A. caama, the marks and lines which
occur on various parts of the body are black, instead of brown as in
the female; in the brindled gnu (A. gorgon) "the colours of the male
are nearly the same as those of the female, only deeper and of a
brighter hue."* Other analogous cases could be added.

  * On the Ant. niger, see Proc. Zool. Soc., 1850, p. 133. With
respect to an allied species, in which there is an equal sexual
difference in colour, see Sir S. Baker, The Albert Nyanza, 1866,
vol. ii., p. 627. For the A. sing-sing, Gray, Cat. B. Mus., p. 100.
Desmarest, Mammalogie, p. 468, on the A. caama. Andrew Smith,
Zoology of S. Africa, on the gnu.

  The banteng bull (Bos sondaicus) of the Malayan Archipelago is
almost black, with white legs and buttocks; the cow is of a bright
dun, as are the young males until about the age of three years, when
they rapidly change colour. The emasculated bull reverts to the colour
of the female. The female kemas goat is paler, and both it and the
female Capra aegagrus are said to be more uniformly tinted than
their males. Deer rarely present any sexual differences in colour.
Judge Caton, however, informs me that in the males of the wapiti
deer (Cervus canadensis) the neck, belly, and legs are much darker
than in the female; but during the winter the darker tints gradually
fade away and disappear. I may here mention that Judge Caton has in
his park three races of the Virginian deer, which differs slightly
in colour, but the differences are almost exclusively confined to
the blue winter or breeding-coat; so that this case may be compared
with those given in a previous chapter of closely-allied or
representative species of birds, which differ from each other only
in their breeding plumage.* The females of Cervus paludosus of S.
America, as well as the young of both sexes, do not possess the
black stripes on the nose and the blackish-brown line on the breast,
which are characteristic of the adult males.*(2) Lastly, as I am
informed by Mr. Blyth, the mature male of the beautifully coloured and
spotted axis deer is considerably darker than the female: and this hue
the castrated male never acquires.

  * Ottawa Academy of Sciences, May 21, 1868, pp. 3,5.
  *(2) S. Muller, on the banteng, Zoog. Indischen Archipel.,
1839-1844, tab. 35; see also Raffles, as quoted by Mr. Blyth, in
Land and Water, 1867, p. 476. On goats, Dr. Gray, Catalogue, of the
British Museum, p. 146; Desmarest, Mammalogie, p. 482. On the Cervus
paludosus, Rengger, ibid., s. 345.

  The last Order which we need consider is that of the primates. The
male of the Lemur macaco is generally coal-black, whilst the female is
brown.* Of the Quadrumana of the New World, the females and young of
Mycetes caraya are greyish-yellow and like each other; in the second
year the young male becomes reddish-brown; in the third, black,
excepting the stomach, which, however, becomes quite black in the
fourth or fifth year. There is also a strongly-marked difference in
colour between the sexes of Mycetes seniculus and Cebus capucinus; the
young of the former, and I believe of the latter species, resembling
the females. With Pithecia leucocephala the young likewise resemble
the females, which are brownish-black above and light rusty-red
beneath, the adult males being black. The ruff of hair round the
face of Ateles marginatus is tinted yellow in the male and white in
the female. Turning to the Old World, the males of Hylobates hoolock
are always black, with the exception of a white band over the brows;
the females vary from whity-brown to a dark tint mixed with black, but
are never wholly black.*(2) In the beautiful Cercopithecus diana,
the head of the adult male is of an intense black, whilst that of
the female is dark grey; in the former the fur between the thighs is
of an elegant fawn colour, in the latter it is paler. In the beautiful
and curious moustache monkey (Cercopithecus cephus) the only
difference between the sexes is that the tail of the male is
chestnut and that of the female grey; but Mr. Bartlett informs me that
all the hues become more pronounced in the male when adult, whilst
in the female they remain as they were during youth. According to
the coloured figures given by Solomon Muller, the male of
Semnopithecus chrysomelas is nearly black, the female being pale
brown. In the Cercopithecus cynosurus and griseoviridis one part of
the body, which is confined to the male sex, is of the most
brilliant blue or green, and contrasts strikingly with the naked
skin on the hinder part of the body, which is vivid red.

  * Sclater, Proc. Zool. Soc., 1866, p. i. The same fact has also been
fully ascertained by M. M. Pollen and van Dam. See, also, Dr. Gray
in Annals and Magazine of Natural History, May, 1871, p. 340.
  *(2) On Mycetes, Rengger, ibid., s. 14; and Brehm, Illustriertes
Thierleben, B. i., ss. 96, 107. On Ateles Desmarest, Mammalogie, p.
75. On Hylobates, Blyth, Land and Water, 1867, p. 135. On the
Semnopithecus, S. Muller, Zoog. Indischen Archipel., tab. x.

  Lastly, in the baboon family, the adult male of Cynocephalus
hamadryas differs from the female not only by his immense mane, but
slightly in the colour of the hair and of the naked callosities. In
the drill (C. leucophaeus) the females and young are much
paler-coloured, with less green, than the adult males. No other member
in the whole class of mammals is coloured in so extraordinary a manner
as the adult male mandrill (C. mormon). The face at this age becomes
of a fine blue, with the ridge and tip of the nose of the most
brilliant red. According to some authors, the face is also marked with
whitish stripes, and is shaded in parts with black, but the colours
appear to be variable. On the forehead there is a crest of hair, and
on the chin a yellow beard. "Toutes les parties superieures de leurs
cuisses et le grand espace nu de leurs fesses sont egalement colores
du rouge le plus vif, avec un melange de bleu qui ne manque reellement
pas d'elegance."* When the animal is excited all the naked parts
become much more vividly tinted. Several authors have used the
strongest expressions in describing these resplendent colours, which
they compare with those of the most brilliant birds. Another
remarkable peculiarity is that when the great canine teeth are fully
developed, immense protuberances of bone are formed on each cheek,
which are deeply furrowed longitudinally, and the naked skin over them
is brilliantly-coloured, as just-described. (See fig. 69.) In the
adult females and in the young of both sexes these protuberances are
scarcely perceptible; and the naked parts are much less bright
coloured, the face being almost black, tinged with blue. In the
adult female, however, the nose at certain regular intervals of time
becomes tinted with red.

  * Gervais, Hist., Nat. des Mammiferes, 1854, p. 103. Figures are
given of the skull of the male. Also Desmarest, Mammalogie, p. 70.
Geoffroy St-Hilaire and F. Cuvier, Hist. Nat. des Mammiferes, 1824,
tom. i.

  In all the cases hitherto given the male is more strongly or
brighter coloured than the female, and differs from the young of
both sexes. But as with some few birds it is the female which is
brighter coloured than the male, so with the rhesus monkey (Macacus
rhesus), the female has a large surface of naked skin round the
tail, of a brilliant carmine red, which, as I was assured by the
keepers in the Zoological Gardens, periodically becomes even yet
more vivid, and her face also is pale red. On the other hand, in the
adult male and in the young of both sexes (as I saw in the Gardens),
neither the naked skin at the posterior end of the body, nor the face,
shew a trace of red. It appears, however, from some published
accounts, that the male does occasionally, or during certain
seasons, exhibit some traces of the red. Although he is thus less
ornamented than the female, yet in the larger size of his body, larger
canine teeth, more developed whiskers, more prominent superciliary
ridges, he follows the common rule of the male excelling the female.
  I have now given all the cases known to me of a difference in colour
between the sexes of mammals. Some of these may be the result of
variations confined to one sex and transmitted to the same sex,
without any good being gained, and therefore without the aid of
selection. We have instances of this with our domesticated animals, as
in the males of certain cats being rusty-red, whilst the females are
tortoise-shell coloured. Amalogous cases occur in nature: Mr. Bartlett
has seen many black varieties of the jaguar, leopard, vulpine
phalanger, and wombat; and he is certain that all, or nearly all these
animals, were males. On the other hand, with wolves, foxes, and
apparently American squirrels, both sexes are occasionally born black.
Hence it is quite possible that with some mammals a difference in
colour between the sexes, especially when this is congenital, may
simply be the result, without the aid of selection, of the
occurrence of one or more variations, which from the first were
sexually limited in their transmission. Nevertheless it is
improbable that the diversified, vivid, and contrasted colours of
certain quadrupeds, for instance, of the above monkeys and
antelopes, can thus be accounted for. We should bear in mind that
these colours do not appear in the male at birth, but only at or
near maturity; and that unlike ordinary variations, they are lost if
the male be emasculated. It is on the whole probable that the
strongly-marked colours and other ornamental characters of male
quadrupeds are beneficial to them in their rivalry with other males,
and have consequently been acquired through sexual selection. This
view is strengthened by the differences in colour between the sexes
occurring almost exclusively, as may be collected from the previous
details, in those groups and sub-groups of mammals which present other
and strongly-marked secondary sexual characters; these being
likewise due to sexual selection.
  Quadrupeds manifestly take notice of colour. Sir S. Baker repeatedly
observed that the African elephant and rhinoceros attacked white or
grey horses with special fury. I have elsewhere shewn* that
half-wild horses apparently prefer to pair with those of the same
colour, and that herds of fallow-deer of different colours, though
living together, have long kept distinct. It is a more significant
fact that a female zebra would not admit the addresses of a male ass
until he was painted so as to resemble a zebra, and then, as John
Hunter remarks, "she received him very readily. In this curious
fact, we have instinct excited by mere colour, which had so strong
an effect as to get the better of everything else. But the male did
not require this, the female being an animal somewhat similar to
himself, was sufficient to rouse him."*(2)

  * The Variation of Animals and Plants under Domestication, 1868,
vol. ii., pp. 102, 103.
  *(2) Essays and Observations, by J. Hunter, edited by Owen, 1861,
i., p. 194.

  In an earlier chapter we have seen that the mental powers of the
higher animals do not differ in kind, though greatly in degree, from
the corresponding powers of man, especially of the lower and barbarous
races; and it would appear that even their taste for the beautiful
is not widely different from that of the Quadrumana. As the negro of
Africa raises the flesh on his face into parallel ridges "or
cicatrices, high above the natural surface, which unsightly
deformities are considered great personal attractions";*- as negroes
and savages in many parts of the world paint their faces with red,
blue, white, or black bars,- so the male mandrill of Africa appears to
have acquired his deeply-furrowed and gaudily-coloured face from
having been thus rendered attractive to the female. No doubt it is
to us a most grotesque notion that the posterior end of the body
should be coloured for the sake of ornament even more brilliantly than
the face; but this is not more strange than that the tails of many
birds should be especially decorated.

  * Sir S. Baker, The Nile Tributaries of Abyssinia, 1867.

  With mammals we do not at present possess any evidence that the
males take pains to display their charms before the female; and the
elaborate manner in which this is performed by male birds and other
animals is the strongest argument in favour of the belief that the
females admire, or are excited by, the ornaments and colours displayed
before them. There is, however, a striking parallelism between mammals
and birds in all their secondary sexual characters, namely in their
weapons for fighting with rival males, in their ornamental appendages,
and in their colours. In both classes, when the male differs from
the female, the young of both sexes almost always resemble each other,
and in a large majority of cases resemble the adult female. In both
classes the male assumes the characters proper to his sex shortly
before the age of reproduction; and if emasculated at an early period,
loses them. In both classes the change of colour is sometimes
seasonal, and the tints of the naked parts sometimes become more vivid
during the act of courtship. In both classes the male is almost always
more vividly or strongly coloured than the female, and is ornamented
with larger crests of hair or feathers, or other such appendages. In a
few exceptional cases the female in both classes is more highly
ornamented than the male. With many mammals, and at least in the
case of one bird, the male is more odoriferous than the female. In
both classes the voice of the male is more powerful than that of the
female. Considering this parallelism, there can be little doubt that
the same cause, whatever it may be, has acted on mammals and birds;
and the result, as far as ornamental characters are concerned, may
be attributed, as it appears to me, to the long-continued preference
of the individuals of one sex for certain individuals of the
opposite sex, combined with their success in leaving a larger number
of offspring to inherit their superior attractions.

  Equal transmission of ornamental characters to both sexes.- With
many birds, ornaments, which analogy leads us to believe were
primarily acquired by the males, have been transmitted equally, or
almost equally, to both sexes; and we may now enquire how far this
view applies to mammals. With a considerable number of species,
especially of the smaller kinds, both sexes have been coloured,
independently of sexual selection, for the sake of protection; but
not, as far as I can judge, in so many cases, nor in so striking a
manner, as in most of the lower classes. Audubon remarks that he often
mistook the musk-rat,* whilst sitting on the banks of a muddy
stream, for a clod of earth, so complete was the resemblance. The hare
on her form is a familiar instance of concealment through colour;
yet this principle partly fails in a closely-allied species, the
rabbit, for when running to its burrow, it is made conspicuous to
the sportsman, and no doubt to all beasts of prey, by its upturned
white tail. No one doubts that the quadrupeds inhabiting snow-clad
regions have been rendered white to protect them from their enemies,
or to favour their stealing on their prey. In regions where snow never
lies for long, a white coat would be injurious; consequently,
species of this colour are extremely rare in the hotter parts of the
world. It deserves notice that many quadrupeds inhabiting moderately
cold regions, although they do not assume a white winter dress, become
paler during this season; and this apparently is the direct result
of the conditions to which they have long been exposed. Pallas*(2)
states that in Siberia a change of this nature occurs with the wolf,
two species of Mustela, the domestic horse, the Equus hemionus, the
domestic cow, two species of antelopes, the musk-deer, the roe, elk,
and reindeer. The roe, for instance, has a red summer and a
greyish-white winter coat; and the latter may perhaps serve as a
protection to the animal whilst wandering through the leafless
thickets, sprinkled with snow and hoar-frost. If the above-named
animals were gradually to extend their range into regions
perpetually covered with snow, their pale winter-coats would
probably be rendered through natural selection, whiter and whiter,
until they became as white as snow.

  * Fiber zibethicus, Audubon and Bachman, The Quadrupeds of North
America, 1846, p. 109.
  *(2) Novae species Quadrupedum e Glirium ordine, 1778, p. 7. What
I have called the roe is the Capreolus sibricus subecaudatus of
Pallas.

  Mr. Reeks has given me a curious instance of an animal profiting
by being peculiarly coloured. He raised from fifty to sixty white
and brown piebald rabbits in a large walled orchard; and he had at the
same time some similarly coloured cats in his house. Such cats, as I
have often noticed, are very conspicuous during day; but as they
used to lie in watch during the dusk at the mouths of the burrows, the
rabbits apparently did not distinguish them from their
parti-coloured brethren. The result was that, within eighteen
months, every one of these parti-coloured rabbits was destroyed; and
there was evidence that this was effected by the cats. Colour seems to
be advantageous to another animal, the skunk, in a manner of which
we have had many instances in other classes. No animal will
voluntarily attack one of these creatures on account of the dreadful
odour which it emits when irritated; but during the dusk it would
not easily be recognized and might be attacked by a beast of prey.
Hence it is, as Mr. Belt believes,* that the skunk is provided with
a great white bushy tail, which serves as a conspicuous warning.

  * The Naturalist in Nicaragua, p. 249.

  Although we must admit that many quadrupeds have received their
present tints either as a protection, or as an aid in procuring
prey, yet with a host of species, the colours are far too
conspicuous and too singularly arranged to allow us to suppose that
they serve for these purposes. We may take as an illustration
certain antelopes; when we see the square white patch on the throat,
the white marks on the fetlocks, and the round black spots on the
ears, all more distinct in the male of the Portax picta, than in the
female;- when we see that the colours are more vivid, that the
narrow white lines on the flank and the broad white bar on the
shoulder are more distinct in the male Oreas derbyanus than in the
female;- when we see a similar difference between the sexes of the
curiously-ornamented Tragelaphus scriptus (see fig. 70),- we cannot
believe that differences of this kind are of any service to either sex
in their daily habits of life. It seems a much more probable
conclusion that the various marks were first acquired by the males and
their colours intensified through sexual selection, and then partially
transferred to the females. If this view be admitted, there can be
little doubt that the equally singular colours and marks of many other
antelopes, though common to both sexes, have been gained and
transmitted in a like manner. Both sexes, for instance, of the
koodoo (Strepsiceros kudu) (see fig. 64) have narrow white vertical
lines on their hind flanks, and an elegant angular white mark on their
foreheads. Both sexes in the genus Damalis are very oddly coloured; in
D. pygarga the back and neck are purplish-red, shading on the flanks
into black; and these colours are abruptly separated from the white
belly and from a large white space on the buttocks; the head is
still more oddly coloured, a large oblong white mask, narrowly-edged
with black, covers the face up to the eyes (see fig. 71); there are
three white stripes on the forehead, and the ears are marked with
white. The fawns of this species are of a uniform pale
yellowish-brown. In Damalis albifrons the colouring of the head
differs from that in the last species in a single white stripe
replacing the three stripes, and in the ears being almost wholly
white.* After having studied to the best of my ability the sexual
differences of animals belonging to all classes, I cannot avoid the
conclusion that the curiously-arranged colours of many antelopes,
though common to both sexes, are the result of sexual selection
primarily applied to the male.

  * See the fine plates in A. Smith's Zoology of South Africa, and Dr.
Gray's Gleanings from the Menagerie of Knowsley.

  The same conclusion may perhaps be extended to the tiger, one of the
most beautiful animals in the world, the sexes of which cannot be
distinguished by colour, even by the dealers in wild beasts. Mr.
Wallace believes* that the striped coat of the tiger "so assimilates
with the vertical stems of the bamboo, as to assist greatly in
concealing him from his approaching prey." But this view does not
appear to me satisfactory. We have some slight evidence that his
beauty may be due to sexual selection, for in two species of Felis the
analogous marks and colours are rather brighter in the male than in
the female. The zebra is conspicuously striped, and stripes cannot
afford any protection in the open plains of South Africa. Burchell*(2)
in describing a herd says, "their sleek ribs glistened in the sun, and
the brightness and regularity of their striped coats presented a
picture of extraordinary beauty, in which probably they are not
surpassed by any other quadruped." But as throughout the whole group
of the Equidae the sexes are identical in colour, we have here no
evidence of sexual selection. Nevertheless he who attributes the white
and dark vertical stripes on the flanks of various antelopes to this
process, will probably extend the same view to the royal tiger and
beautiful zebra.

  * Westminster Review, July 1, 1867, p. 5.
  *(2) Travels in South Africa, 1824, vol. ii., p. 315.

  We have seen in a former chapter that when young animals belonging
to any class follow nearly the same habits of life as their parents,
and yet are coloured in a different manner, it may be inferred that
they have retained the colouring of some ancient and extinct
progenitor. In the family of pigs, and in the tapirs, the young are
marked with longitudinal stripes, and thus differ from all the
existing adult species in these two groups. With many kinds of deer
the young are marked with elegant white spots, of which their
parents exhibit not a trace. A graduated series can be followed from
the axis deer, both sexes of which at all ages and during all
seasons are beautifully spotted (the male being rather more strongly
coloured than the female), to species in which neither the old nor the
young are spotted. I will specify some of the steps in this series.
The Manchurian deer (Cervus mantchuricus) is spotted during the
whole year, but, as I have seen in the Zoological Gardens, the spots
are much plainer during the summer, when the general colour of the
coat is lighter, than during the winter, when the general colour is
darker and the horns are fully developed. In the hog-deer (Hyelaphus
porcinus) the spots are extremely conspicuous during the summer when
the coat is reddish-brown, but quite disappear during the winter
when the coat is brown.* In both these species the young are
spotted. In the Virginian deer the young are likewise spotted, and
about five per cent of the adult animals living in Judge Caton's park,
as I am informed by him, temporarily exhibit at the period when the
red summer coat is being replaced by the bluish winter coat, a row
of spots on each flank, which are always the same in number, though
very variable in distinctness. From this condition there is but a very
small step to the complete absence of spots in the adults at all
seasons; and, lastly, to their absence at all ages and seasons, as
occurs with certain species. From the existence of this perfect
series, and more especially from the fawns of so many species being
spotted, we may conclude that the now living members of the deer
family are the descendants of some ancient species which, like the
axis deer, was spotted at all ages and seasons. A still more ancient
progenitor probably somewhat resembled the Hyomoschus aquaticus- for
this animal is spotted, and the hornless males have large exserted
canine teeth, of which some few true deer still retain rudiments.
Hyomoschus, also, offers one of those interesting cases of a form
linking together two groups, for it is intermediate in certain
osteological characters between the pachyderms and ruminants, which
were formerly thought to be quite distinct.*(2)

  * Dr. Gray, Gleanings from the Menagerie of Knowsley, p. 64. Mr.
Blyth, in speaking (Land and Water, 1869, p. 42) of the hog-deer of
Ceylon, says it is more brightly spotted with white than the common
hog-deer, at the season when it renews its horns.
  *(2) Falconer and Cautley, Proc. Geolog. Soc., 1843; and
Falconer's Pal. Memoirs, vol. i., p. 196.

  A curious difficulty here arises. If we admit that coloured spots
and stripes were first acquired as ornaments, how comes it that so
many existing deer, the descendants of an aboriginally spotted animal,
and all the species of pigs and tapirs, the descendants of an
aboriginally striped animal, have lost in their adult state their
former ornaments? I cannot satisfactorily answer this question. We may
feel almost sure that the spots and stripes disappeared at or near
maturity in the progenitors of our existing species, so that they were
still retained by the young; and owing to the law of inheritance at
corresponding ages, were transmitted to the young of all succeeding
generations. It may have been a great advantage to the lion and
puma, from the open nature of their usual haunts, to have lost their
stripes, and to have been thus rendered less conspicuous to their
prey; and if the successive variations, by which this end was
gained, occurred rather late in life, the young would have retained
their stripes, as is now the case. As to deer, pigs, and tapirs, Fritz
Muller has suggested to me that these animals, by the removal of their
spots or stripes through natural selection, would have been less
easily seen by their enemies; and that they would have especially
required this protection, as soon as the Carnivora increased in size
and number during the tertiary periods. This may be the true
explanation, but it is rather strange that the young should not have
been thus protected, and still more so that the adults of some species
should have retained their spots, either partially or completely,
during part of the year. We know that, when the domestic ass varies
and becomes reddish-brown, grey, or black, the stripes on the
shoulders and even on the spine frequently disappear, though we cannot
explain the cause. Very few horses, except dun-coloured kinds, have
stripes on any part of their bodies, yet we have good reason to
believe that the aboriginal horse was striped on the legs and spine,
and probably on the shoulders.* Hence the disappearance of the spots
and stripes in our adult existing deer, pigs, and tapirs, may be due
to a change in the general colour of their coats; but whether this
change was effected through sexual or natural selection, or was due to
the direct action of the conditions of life, or to some other
unknown cause, it is impossible to decide. An observation made by
Mr. Sclater well illustrates our ignorance of the laws which
regulate the appearance and disappearance of stripes; the species of
Asinus which inhabit the Asiatic continent are destitute of stripes,
not having even the cross shoulder-stripe, whilst those which
inhabit Africa are conspicuously striped, with the partial exception
of A. taeniopus, which has only the cross shoulder-stripe and
generally some faint bars on the legs; and this species inhabits the
almost intermediate region of Upper Egypt and Abyssinia.*(2)

  * 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.