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Chapter XVIII
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 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.
The voice of the adult male gorilla is tremendous, and he is furnished with
a laryngeal sack, as is the adult male orang. (4. Owen 'Anatomy of
Vertebrates,' vol. iii. p. 600.) 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. (5. Mr.
Green, in 'Journal of Linnean Society,' vol. x. 'Zoology,' 1869, note 362.)
Another gibbon, the H. agilis, is remarkable, from having the power of
giving a complete and correct octave of musical notes (6. C.L. Martin,
'General Introduction to the Natural History of Mamm. Animals,' 1841, p.
431.), 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 (7. 'Naturgeschichte der Saugethiere von
Paraguay,' 1830, ss. 15, 21.), 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.
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 is 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. (8. 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 (9. 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 in 'Proceedings of the Zoological Society' 1873, p. 241.),
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.
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. (10. Rengger, 'Naturgeschichte der
Saugethiere von Paraguay,' 1830, s. 355. This observer also gives some
curious particulars in regard to the odour.) 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." (11. 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.) 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. (12. Pallas,
'Spicilegia Zoolog.' fasc. xiii. 1799, 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 (13.
Dr. Gray, 'Gleanings from the Menagerie at Knowsley,' pl. 28.) (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 (14.
Judge Caton on the Wapiti, 'Transact. Ottawa Acad. Nat. Sciences,' 1868,
pp. 36, 40; Blyth, 'Land and Water,' on Capra aegagrus 1867, p. 37.); 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.
[Fig. 68. Pithecia satanas, male (from Brehm).]
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. (15. Hunter's 'Essays and
Observations,' edited by Owen, 1861. vol. i. p. 236.) 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 is so small at other times that it may be
called rudimentary. (16. See Dr. Gray's 'Catalogue of Mammalia in the
British Museum,' part iii. 1852, p. 144.) 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 (Fig. 68). So
it is with the whiskers of some species of Macacus (17. Rengger,
'Saugthiere,' etc., s. 14; Desmarest, 'Mammalogie,' p. 86.), 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.
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. (18. 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 Berbura goat, see Dr. Gray,
'Catalogue,' ibid. p. 157.) 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, etc., 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.
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." (19.
Osphranter rufus, Gould, 'Mammals of Australia,' 1863, vol. ii. On the
Didelphis, Desmarest, 'Mammalogie,' p. 256.) 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." (20. 'Annals and Magazine of Natural
History,' Nov. 1867, p. 325. On the Mus minutus, Desmarest, 'Mammalogie,'
p. 304.) 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. (21. 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.) 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."
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."
(22. Desmarest, 'Mammalogie,' 1820, p. 220. On Felis mitis, Rengger,
ibid. s. 194.) 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." (23. 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 (24. Judge Caton, in 'Transactions of the Ottawa Academy of
Natural Sciences,' 1868, p. 4.) 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. (25. 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,' pl. 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."
(26. 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.)
Other analogous cases could be added.
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 differ 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. (27. 'Ottawa
Academy of Sciences,' May 21, 1868, pp. 3, 5.) 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. (28. 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.) 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.
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. (29.
Sclater, 'Proc. Zool. Soc.' 1866, p. i. The same fact has also been fully
ascertained by MM. Pollen and van Dam. See, also, Dr. Gray in 'Annals and
Magazine of Natural History,' May 1871, p. 340.) 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.
(30. On Mycetes, Rengger, ibid. s. 14; and Brehm, 'Thierleben,' B. i. s.
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.) 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 griseo-viridis 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.
[Fig. 69. Head of male Mandrill (from Gervais, 'Hist. Nat. des
Mammiferes').]
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." (31. 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.) 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. (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.
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.
Analogous 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 (32. The 'Variation of
Animals and Plants under Domestication,' 1868, vol. ii. pp. 102, 103.) 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." (33. 'Essays and Observations,'
by J. Hunter, edited by Owen, 1861, vol. 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" (34. Sir S. Baker, 'The Nile Tributaries of Abyssinia,'
1867.);--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.
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 (35. Fiber zibethicus,
Audubon and Bachman, 'The Quadrupeds of North America,' 1846, p. 109.),
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 (36. 'Novae species Quadrupedum e
Glirium ordine,' 1778, p. 7. What I have called the roe is the Capreolus
sibiricus subecaudatus of Pallas.) 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.
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
recognised and might be attacked by a beast of prey. Hence it is, as Mr.
Belt believes (37. 'The Naturalist in Nicaragua,' p. 249.), that the skunk
is provided with a great white bushy tail, which serves as a conspicuous
warning.
[Fig. 70. Tragelaphus scriptus, male (from the Knowsley Menagerie).
Fig. 71. Damalis pygarga, male (from the Knowsley Menagerie).]
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 (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) (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 (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. (38. See the fine
plates in A. Smith's 'Zoology of South Africa,' and Dr. Gray's 'Gleanings
from the Menagerie of Knowsley.') 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.
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 (39.
'Westminster Review,' July 1, 1867, p. 5.) 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 (40. 'Travels in
South Africa,' 1824, vol. ii. p. 315.) 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.
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
Mantchurian 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. (41. 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.) 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. (42.
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. (43. The 'Variation of Animals and Plants under
Domestication,' 1868, vol. i. pp. 61-64.) 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. (44. 'Proc. Zool. Soc.'
1862, p. 164. See, also, Dr. Hartmann, 'Ann. d. Landw.' Bd. xliii. s.
222.)
QUADRUMANA.
[Fig. 72. Head of Semnopithecus rubicundus. This and the following
figures (from Prof. Gervais) are given to shew the odd arrangement and
development of the hair on the head.
Fig. 73. Head of Semnopithecus comatus.
Fig. 74. Head of Cebus capucinus.
Fig. 75. Head of Ateles marginatus.
Fig. 76. Head of Cebus vellerosus.]
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 (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.
[Fig. 77. Cercopithecus petaurista (from Brehm).]
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 (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 (45.
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.), 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. (46. Bates, 'The Naturalist on the Amazons,'
1863, vol. ii. p. 310.) 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.
[Fig. 78. Cercopithecus diana (from Brehm).]
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 (Fig. 78);
the general colour of the fur is grey; the chest and inner surface of the
forelegs 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 wit
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