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Library: Historical Documents: Charles Darwin: Descent of Man: Chapter 18


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Descent of Man [ 1871 ]

Charles Darwin [ 1809 - 1882 ]

 

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.




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