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