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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2889 times)
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« Reply #180 on: February 10, 2009, 01:24:09 pm »

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

  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.
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