We may therefore conclude that the females of distinct though allied

species have often had their plumage rendered more or less different by

the transference in various degrees, of characters acquired, both during

former and recent times, by the males through sexual selection. But it

deserves especial attention that brilliant colours have been transferred

much more rarely than other tints. For instance, the male of the

red-throated bluebreast (_Cyanecula suecica_) has a rich blue breast,

including a sub-triangular red mark; now marks of approximately the same

shape have been transferred to the female, but the central space is

fulvous instead of red, and is surrounded by mottled instead of blue

feathers. The Gallinaceae offer many analogous cases; for none of the

species, such as partridges, quails, guinea-fowls, &c., in which the

colours of the plumage have been largely transferred from the male to

the female, are brilliantly coloured. This is well exemplified with the

pheasants, in which the male is generally so much more brilliant than

the female; but with the Eared and Cheer pheasants (_Crossoptilon_

_auritum_ and _Phasianus Wallichii_) the two sexes closely resemble each

other and their colours are dull. We may go so far as to believe that if

any part of the plumage in the males of these two pheasants had been

brilliantly coloured, this would not have been transferred to the

females. These facts strongly support Mr. Wallace's view that with birds

which are exposed to much danger during nidification, the transference

of bright colours from the male to the female has been checked through

natural selection. We must not, however, forget that another

explanation, before given, is possible; namely, that the males which

varied and became bright, whilst they were young and inexperienced,

would have been exposed to much danger, and would generally have been

destroyed; the older and more cautious males, on the other hand, if they

varied in a like manner, would not only have been able to survive, but

would have been favoured in their rivalry with other males. Now

variations occurring late in life tend to be transmitted exclusively to

the same sex, so that in this case extremely bright tints would not have

been transmitted to the females. On the other hand, ornaments of a less

conspicuous kind, such as those possessed by the Eared and Cheer

pheasants, would not have been dangerous, and if they appeared during

early youth, would generally have been transmitted to both sexes.

In addition to the effects of the partial transference of characters

from the males to the females, some of the differences between the

females of closely-allied species may be attributed to the direct or

definite action of the conditions of life.[239] With the males any such

action would generally have been masked by the brilliant colours gained

through sexual selection; but not so with the females. Each of the

endless diversities in plumage, which we see in our domesticated birds

is, of course, the result of some definite cause; and under natural and

more uniform conditions, some one tint, assuming that it was in no way

injurious, would almost certainly sooner or later prevail. The free

intercrossing of the many individuals belonging to the same species

would ultimately tend to make any change of colour, thus induced,

uniform in character.

No one doubts that both sexes of many birds have had their colours

adapted for the sake of protection; and it is possible that the females

alone of some species may have been thus modified. Although it would be

a difficult, perhaps an impossible process, as shewn in the last

chapter, to convert through selection one form of transmission into

another, there would not be the least difficulty in adapting the colours

of the female, independently of those of the male, to surrounding

objects, through the accumulation of variations which were from the

first limited in their transmission to the female sex. If the variations

were not thus limited, the bright tints of the male would be

deteriorated or destroyed. Whether the females alone of many species

have been thus specially modified, is at present very doubtful. I wish I

could follow Mr. Wallace to the full extent; for the admission would

remove some difficulties. Any variations which were of no service to the

female as a protection would be at once obliterated, instead of being

lost simply by not being selected, or from free intercrossing, or from

being eliminated when transferred to the male and in any way injurious

to him. Thus the plumage of the female would be kept constant in

character. It would also be a relief if we could admit that the obscure

tints of both sexes of many birds had been acquired and preserved for

the sake of protection,--for example, of the hedge-warbler or kitty-wren

(_Accentor modularis_ and _Troglodytes vulgaris_), with respect to which

we have no sufficient evidence of the action of sexual selection. We

ought, however, to be cautious in concluding that colours which appear

to us dull, are not attractive to the females of certain species; we

should bear in mind such cases as that of the common house-sparrow, in

which the male differs much from the female, but does not exhibit any

bright tints. No one probably will dispute that many gallinaceous birds

which live on the open ground have acquired their present colours, at

least in part, for the sake of protection. We know how well they are

thus concealed; we know that ptarmigans, whilst changing from their

winter to their summer plumage, both of which are protective, suffer

greatly from birds of prey. But can we believe that the very slight

differences in tints and markings between, for instance, the female

black and red-grouse serve as a protection? Are partridges, as they are

now coloured, better protected than if they had resembled quails? Do the

slight differences between the females of the common pheasant, the Japan

and golden pheasants, serve as a protection, or might not their plumages

have been interchanged with impunity? From what Mr. Wallace has observed

of the habits of certain gallinaceous birds in the East he thinks that

such slight differences are beneficial. For myself, I will only say that

I am not convinced.

Formerly when I was inclined to lay much stress on the principle of

protection, as accounting for the less bright colours of female birds,

it occurred to me that possibly both sexes and the young might

aboriginally have been brightly coloured in an equal degree; but that

subsequently, the females from the danger incurred during incubation,

and the young from being inexperienced, had been rendered dull as a

protection. But this view is not supported by any evidence, and is not

probable; for we thus in imagination expose during past times the

females and the young to danger, from which it has subsequently been

necessary to shield their modified descendants. We have, also, to

reduce, through a gradual process of selection, the females and the

young to almost exactly the same tints and markings, and to transmit

them to the corresponding sex and period of life. It is also a somewhat

strange fact, on the supposition that the females and the young have

partaken during each stage of the process of modification of a tendency

to be as brightly coloured as the males, that the females have never

been rendered dull-coloured without the young participating in the same

change; for there are no instances, as far as I can discover, of species

with the females dull-coloured and the young bright-coloured. A partial

exception, however, is offered by the young of certain woodpeckers, for

they have "the whole upper part of the head tinged with red," which

afterwards either decreases into a mere circular red line in the adults

of both sexes, or quite disappears in the adult females.[240]

Finally, with respect to our present class of cases, the most probable

view appears to be that successive variations in brightness or in other

ornamental characters, occurring in the males at a rather late period of

life have alone been preserved; and that most or all of these variations

owing to the late period of life at which they appeared, have been from

the first transmitted only to the adult male offspring. Any variations

in brightness which occurred in the females or in the young would have

been of no service to them, and would not have been selected; moreover,

if dangerous, would have been eliminated. Thus the females and the young

will either have been left unmodified, or, and this has much more

commonly occurred, will have been partially modified by receiving

through transference from the males some of the successive variations.

Both sexes have perhaps been directly acted on by the conditions of life

to which they have long been exposed; but the females from not being

otherwise much modified will best exhibit any such effects. These

changes and all others will have been kept uniform by the free

intercrossing of many individuals. In some cases, especially with ground

birds, the females and the young may possibly have been modified,

independently of the males, for the sake of protection, so as to have

acquired the same dull-coloured plumage.

CLASS II. _When the adult female is more conspicuous than the adult

male, the young of both sexes in their first plumage resemble the adult

male._--This class is exactly the reverse of the last, for the females

are here more brightly coloured or more conspicuous than the males; and

the young, as far as they are known, resemble the adult males instead of

the adult females. But the difference between the sexes is never nearly

so great as occurs with many birds in the first class, and the cases are

comparatively rare. Mr. Wallace who first called attention to the

singular relation which exists between the less bright colours of the

males and their performing the duties of incubation, lays great stress

on this point,[241] as a crucial test that obscure colours have been

acquired for the sake of protection during the period of nesting. A

different view seems to me more probable. As the cases are curious and

not numerous, I will briefly give all that I have been able to find.

In one section of the genus Turnix, quail-like birds, the female is

invariably larger than the male (being nearly twice as large in one of

the Australian species) and this is an unusual circumstance with the

Gallinaceae. In most of the species the female is more distinctly

coloured and brighter than the male,[242] but in some few species the

sexes are alike. In _Turnix taigoor_ of India the male "wants the black

on the throat and neck, and the whole tone of the plumage is lighter and

less pronounced than that of the female." The female appears to be more

vociferous, and is certainly much more pugnacious than the male; so that

the females and not the males are often kept by the natives for

fighting, like game-cocks. As male birds are exposed by the English

bird-catchers for a decoy near a trap, in order to catch other males by

exciting their rivalry, so the females of this Turnix are employed in

India. When thus exposed the females soon begin their "loud purring

call, which can be heard a long way off, and any females within ear-shot

run rapidly to the spot, and commence fighting with the caged bird." In

this way from twelve to twenty birds, all breeding-females, may be

caught in the course of a single day. The natives assert that the

females after laying their eggs associate in flocks, and leave the males

to sit on them. There is no reason to doubt the truth of this assertion,

which is supported by some observations made in China by Mr.

Swinhoe.[243] Mr. Blyth believes, that the young of both sexes resemble

the adult male.

[Illustration: Fig. 60. Rhynchaea capensis (from Brehm).]

The females of the three species of Painted Snipes (Rhynchaea) "are not

only larger, but much more richly coloured than the males."[244] With

all other birds, in which the trachea differs in structure in the two

sexes it is more developed and complex in the male than in the female;

but in the _Rhynchaea Australis_ it is simple in the male, whilst in the

female it makes four distinct convolutions before entering the

lungs.[245] The female therefore of this species has acquired an

eminently masculine character. Mr. Blyth ascertained, by examining many

specimens, that the trachea is not convoluted in either sex of _R.

Bengalensis_, which species so closely resembles _R. Australis_ that it

can hardly be distinguished except by its shorter toes. This fact is

another striking instance of the law that secondary sexual characters

are often widely different in closely-allied forms; though it is a very

rare circumstance when such differences relate to the female sex. The

young of both sexes of _R. Bengalensis_ in their first plumage are said

to resemble the mature male.[246] There is also reason to believe that

the male undertakes the duty of incubation, for Mr. Swinhoe[247] found

the females before the close of the summer associated in flocks, as

occurs with the females of the Turnix.

The females of _Phalaropus fulicarius_ and _P. hyperboreus_ are larger,

and in their summer plumage "more gaily attired than the males." But the

difference in colour between the sexes is far from conspicuous. The male

alone of _P. fulicarius_ undertakes, according to Professor Steenstrup,

the duty of incubation, as is likewise shewn by the state of his

breast-feathers during the breeding-season. The female of the dotterel

plover (_Eudromias morinellus_) is larger than the male, and has the red

and black tints on the lower surface, the white crescent on the breast,

and the stripes over the eyes, more strongly pronounced. The male also

takes at least a share in hatching the eggs; but the female likewise

attends to the young.[248] I have not been able to discover whether with

these species the young resemble the adult males more closely than the

adult females; for the comparison is somewhat difficult to make on

account of the double moult.

Turning now to the Ostrich order: the male of the common cassowary

(_Casuarius galeatus_) would be thought by any one to be the female,

from his smaller size and from the appendages and naked skin about his

head being much less brightly coloured; and I am informed by Mr.

Bartlett that in the Zoological Gardens it is certainly the male alone

who sits on the eggs and takes care of the young.[249] The female is

said by Mr. T. W. Wood[250] to exhibit during the breeding-season a most

pugnacious disposition; and her wattles then become enlarged and more

brilliantly coloured. So again the female of one of the emus

(_Dromoeus irroratus_) is considerably larger than the male, and she

possesses a slight top-knot, but is otherwise undistinguishable in

plumage. She appears, however, "to have greater power, when angry or

otherwise excited, of erecting, like a turkey-cock, the feathers of her

neck and breast. She is usually the more courageous and pugilistic. She

makes a deep hollow guttural boom, especially at night, sounding like a

small gong. The male has a slenderer frame and is more docile, with no

voice beyond a suppressed hiss when angry, or a croak." He not only

performs the whole duty of incubation, but has to defend the young from

their mother; "for as soon as she catches sight of her progeny she

becomes violently agitated, and notwithstanding the resistance of the

father appears to use her utmost endeavours to destroy them. For months

afterwards it is unsafe to put the parents together, violent quarrels

being the inevitable result, in which the female generally comes off

conqueror."[251] So that with this emu we have a complete reversal not

only of the parental and incubating instincts, but of the usual moral

qualities of the two sexes; the females being savage, quarrelsome and

noisy, the males gentle and good. The case is very different with the

African ostrich, for the male is somewhat larger than the female and has

finer plumes with more strongly contrasted colours; nevertheless he

undertakes the whole duty of incubation.[252]

I will specify the few other cases known to me, in which the female is

more conspicuously coloured than the male, although nothing is known

about their manner of incubation. With the carrion-hawk of the Falkland

Islands (_Milvago leucurus_) I was much surprised to find by dissection

that the individuals, which had all their tints strongly pronounced,

with the cere and legs orange-coloured, were the adult females; whilst

those with duller plumage and grey legs were the males or the young. In

an Australian tree-creeper (_Climacteris erythrops_) the female differs

from the male in "being adorned with beautiful, radiated, rufous

markings on the throat, the male having this part quite plain." Lastly

in an Australian nightjar "the female always exceeds the male in size

and in the brilliance of her tints; the males, on the other hand, have

two white spots on the primaries more conspicuous than in the

female."[253]

We thus see that the cases in which female birds are more conspicuously

coloured than the males, with the young in their immature plumage

resembling the adult males instead of the adult females, as in the

previous class, are not numerous, though they are distributed in various

Orders. The amount of difference, also, between the sexes is

incomparably less than that which frequently occurs in the last class;

so that the cause of the difference, whatever it may have been, has

acted on the females in the present class either less energetically or

less persistently than on the males in the last class. Mr. Wallace

believes that the males have had their colours rendered less

conspicuous for the sake of protection during the period of incubation;

but the difference between the sexes in hardly any of the foregoing

cases appears sufficiently great for this view to be safely accepted. In

some of the cases the brighter tints of the female are almost confined

to the lower surface, and the males, if thus coloured, would not have

been exposed to danger whilst sitting on the eggs. It should also be

borne in mind that the males are not only in a slight degree less

conspicuously coloured than the females, but are of less size, and have

less strength. They have, moreover, not only acquired the maternal

instinct of incubation, but are less pugnacious and vociferous than the

females, and in one instance have simpler vocal organs. Thus an almost

complete transposition of the instincts, habits, disposition, colour,

size, and of some points of structure, has been effected between the two

sexes.

Now if we might assume that the males in the present class have lost

some of that ardour which is usual to their sex, so that they no longer

search eagerly for the females; or, if we might assume that the females

have become much more numerous than the males--and in the case of one

Indian Turnix the females are said to be "much more commonly met with

than the males"[254]--then it is not improbable that the females would

have been led to court the males, instead of being courted by them. This

indeed is the case to a certain extent, with some birds, as we have seen

with the peahen, wild turkey, and certain kinds of grouse. Taking as our

guide the habits of most male birds, the greater size and strength and

the extraordinary pugnacity of the females of the Turnix and Emu, must

mean that they endeavour to drive away rival females, in order to gain

possession of the male; and on this view, all the facts become clear;

for the males would probably be most charmed or excited by the females

which were the most attractive to them by their brighter colours, other

ornaments, or vocal powers. Sexual selection would then soon do its

work, steadily adding to the attractions of the females; the males and

the young being left not at all, or but little modified.

CLASS III. _When the adult male resembles the adult female, the young of

both sexes have a peculiar first plumage of their own._--In this class

both sexes when adult resemble each other, and differ from the young.

This occurs with many birds of many kinds. The male robin can hardly be

distinguished from the female, but the young are widely different with

their mottled dusky-olive and brown plumage. The male and female of the

splendid scarlet Ibis are alike, whilst the young are brown; and the

scarlet-colour, though common to both sexes, is apparently a sexual

character, for it is not well developed with birds under confinement, in

the same manner as often occurs in the case of brilliantly coloured male

birds. With many species of herons the young differ greatly from the

adults, and their summer plumage, though common to both sexes, clearly

has a nuptial character. Young swans are slate-coloured, whilst the

mature birds are pure white; but it would be superfluous to give

additional instances. These differences between the young and the old

apparently depend, as in the two last classes, on the young having

retained a former or ancient state of plumage, which has been exchanged

for a new plumage by the old of both sexes. When the adults are brightly

coloured, we may conclude from the remarks just made in relation to the

scarlet ibis and to many herons, and from the analogy of the species in

the first class, that such colours have been acquired through sexual

selection by the nearly mature males; but that, differently from what

occurs in the two first classes, the transmission, though limited to the

same age, has not been limited to the same sex. Consequently both sexes

when mature resemble each other and differ from the young.

CLASS IV. _When the adult male resembles the adult female, the young of

both sexes in their first plumage resemble the adults._--In this class

the young and the adults of both sexes, whether brilliantly or obscurely

coloured, resemble each other. Such cases are, I think, more common than

those in the last class. We have in England instances in the kingfisher,

some woodpeckers, the jay, magpie, crow, and many small dull-coloured

birds, such as the hedge-warbler or kitty-wren. But the similarity in

plumage between the young and the old is never absolutely complete, and

graduates away into dissimilarity. Thus the young of some members of the

kingfisher family are not only less vividly coloured than the adults,

but many of the feathers on the lower surface are edged with

brown,[255]--a vestige probably of a former state of the plumage.

Frequently in the same group of birds, even within the same genus, for

instance in an Australian genus of parrakeets (Platycercus), the young

of some species closely resemble, whilst the young of other species

differ considerably from their parents of both sexes, which are

alike.[256] Both sexes and the young of the common jay are closely

similar; but in the Canada jay (_Perisoreus canadensis_) the young

differ so much from their parents that they were formerly described as

distinct species.[257]

Before proceeding, I may remark that under the present and two next

classes of cases the facts are so complex, and the conclusions so

doubtful, that any one who feels no especial interest in the subject had

better pass them over.

The brilliant or conspicuous colours which characterise many birds in

the present class, can rarely or never be of service to them as a

protection; so that they have probably been gained by the males through

sexual selection, and then transferred to the females and the young. It

is, however, possible that the males may have selected the more

attractive females; and if these transmitted their characters to their

offspring of both sexes, the same results would follow as from the

selection of the more attractive males by the females. But there is some

evidence that this contingency has rarely, if ever, occurred in any of

those groups of birds, in which the sexes are generally alike; for if

even a few of the successive variations had failed to be transmitted to

both sexes, the females would have exceeded to a slight degree the males

in beauty. Exactly the reverse occurs under nature; for in almost every

large group, in which the sexes generally resemble each other, the males

of some few species are in a slight degree more brightly coloured than

the females. It is again possible that the females may have selected the

more beautiful males, these males having reciprocally selected the more

beautiful females; but it is doubtful whether this double process of

selection would be likely to occur, owing to the greater eagerness of

one sex than the other, and whether it would be more efficient than

selection on one side alone. It is, therefore, the most probable view

that sexual selection has acted, in the present class, as far as

ornamental characters are concerned, in accordance with the general

rule throughout the animal kingdom, that is, on the males; and that

these have transmitted their gradually-acquired colours, either equally

or almost equally, to their offspring of both sexes.

Another point is more doubtful, namely, whether the successive

variations first appeared in the males after they had become nearly

mature, or whilst quite young. In either case sexual selection must have

acted on the male when he had to compete with rivals for the possession

of the female; and in both cases the characters thus acquired have been

transmitted to both sexes and all ages. But these characters, if

acquired by the males when adult, may have been transmitted at first to

the adults alone, and at some subsequent period transferred to the

young. For it is known that when the law of inheritance at corresponding

ages fails, the offspring often inherit characters at an earlier age

than that at which they first appeared in their parents.[258] Cases

apparently of this kind have been observed with birds in a state of

nature. For instance Mr. Blyth has seen specimens of _Lanius rufus_ and

of _Colymbus glacialis_ which had assumed whilst young, in a quite

anomalous manner, the adult plumage of their parents.[259] Again, the

young of the common swan (_Cygnus olor_) do not cast off their dark

feathers and become white until eighteen months or two years old; but

Dr. F. Forel has described the case of three vigorous young birds, out

of a brood of four, which were born pure white. These young birds were

not albinoes, as shewn by the colour of their beaks and legs, which

nearly resembled the same parts in the adults.[260]

It may be worth while to illustrate the above three modes by which, in

the present class, the two sexes and the young may have come to resemble

each other, by the curious case of the genus Passer.[261] In the

house-sparrow (_P. domesticus_) the male differs much from the female

and from the young. These resemble each other, and likewise to a large

extent both sexes and the young of the sparrow of Palestine (_P.

brachydactylus_), as well as of some allied species. We may therefore

assume that the female and young of the house-sparrow approximately shew

us the plumage of the progenitor of the genus. Now with the tree-sparrow

(_P. montanus_) both sexes and the young closely resemble the male of

the house-sparrow; so that they have all been modified in the same

manner, and all depart from the typical colouring of their early

progenitor. This may have been effected by a male ancestor of the

tree-sparrow having varied, firstly, when nearly mature, or, secondly,

whilst quite young, having in either case transmitted his modified

plumage to the females and the young; or, thirdly, he may have varied

when adult and transmitted his plumage to both adult sexes, and, owing

to the failure of the law of inheritance at corresponding ages, at some

subsequent period to his young.

It is impossible to decide which of these three modes has generally

prevailed throughout the present class of cases. The belief that the

males varied whilst young, and transmitted their variations to their

offspring of both sexes is perhaps the most probable. I may here add

that I have endeavoured, with little success, by consulting various

works, to decide how far with birds the period of variation has

generally determined the transmission of characters to one sex or to

both. The two rules, often referred to (namely, that variations

occurring late in life are transmitted to one and the same sex, whilst

those which occur early in life are transmitted to both sexes),

apparently hold good in the first,[262] second, and fourth classes of

cases; but they fail in an equal number, namely, in the third, often in

the fifth,[263] and in the sixth small class. They hold good, however,

as far as I can judge, with a considerable majority of the species of

birds. Whether or not this be so, we may conclude from the facts given

in the eighth chapter that the period of variation has been one

important element in determining the form of transmission.

With birds it is difficult to decide by what standard we ought to judge

of the earliness or lateness of the period of variation, whether by the

age in reference to the duration of life, or to the power of

reproduction, or to the number of moults through which the species

passes. The moulting of birds, even within the same family, sometimes

differs much without any assignable cause. Some birds moult so early,

that nearly all the body-feathers are cast off before the first

wing-feathers are fully grown; and we cannot believe that this was the

primordial state of things. When the period of moulting has been

accelerated, the age at which the colours of the adult plumage were

first developed would falsely appear to us to have been earlier than it

really was. This may be illustrated by the practice followed by some

bird-fanciers, who pull out a few feathers from the breast of nestling

bullfinches, and from the head or neck of young gold-pheasants, in order

to ascertain their sex; for in the males these feathers are immediately

replaced by coloured ones.[264] The actual duration of life is known in

but few birds, so that we can hardly judge by this standard. And with

reference to the period at which the powers of reproduction are gained,

it is a remarkable fact that various birds occasionally breed whilst

retaining their immature plumage.[265]

The fact of birds breeding in their immature plumage seems opposed to

the belief that sexual selection has played as important a part, as I

believe it has, in giving ornamental colours, plumes, &c., to the males,

and, by means of equal transmission, to the females of many species. The

objection would be a valid one, if the younger and less ornamented males

were as successful in winning females and propagating their kind, as the

older and more beautiful males. But we have no reason to suppose that

this is the case. Audubon speaks of the breeding of the immature males

of _Ibis tantalus_ as a rare event, as does Mr. Swinhoe, in regard to

the immature males of Oriolus.[266] If the young of any species in their

immature plumage were more successful in winning partners than the

adults, the adult plumage would probably soon be lost, as the males

which retained their immature dress for the longest period would

prevail, and thus the character of the species would ultimately be

modified.[267] If, on the other hand, the young never succeeded in

obtaining a female, the habit of early reproduction would perhaps be

sooner or later quite eliminated, from being superfluous and entailing

waste of power.

The plumage of certain birds goes on increasing in beauty during many

years after they are fully mature; this is the case with the train of

the peacock, and with the crest and plumes of certain herons; for

instance, the _Ardea Ludovicana_;[268] but it is very doubtful whether

the continued development of such feathers is the result of the

selection of successive beneficial variations, or merely of continuous

growth. Most fishes continue increasing in size, as long as they are in

good health and have plenty of food; and a somewhat similar law may

prevail with the plumes of birds.

CLASS V. _When the adults of both sexes have a distinct winter and

summer plumage, whether or not the male differs from the female, the

young resemble the adults of both sexes in their winter dress, or much

more rarely in their summer dress, or they resemble the females alone;

or the young may have an intermediate character; or again, they may

differ greatly from the adults in both their seasonal plumages._--The

cases in this class are singularly complex; nor is this surprising, as

they depend on inheritance, limited in a greater or less degree in three

different ways, namely by sex, age, and the season of the year. In some

cases the individuals of the same species pass through at least five

distinct states of plumage. With the species, in which the male differs

from the female during the summer season alone, or, which is rarer,

during both seasons,[269] the young generally resemble the females,--as

with the so-called goldfinch of North America, and apparently with the

splendid Maluri of Australia.[270] With the species, the sexes of which

are alike during both the summer and winter, the young may resemble the

adults, firstly, in their winter dress; secondly, which occurs much more

rarely, in their summer dress; thirdly, they may be intermediate between

these two states; and, fourthly, they may differ greatly from the adults

at all seasons. We have an instance of the first of these four cases in

one of the egrets of India (_Buphus coromandus_), in which the young and

the adults of both sexes are white during the winter, the adults

becoming golden-buff during the summer. With the Gaper (_Anastomus

oscitans_) of India we have a similar case, but the colours are

reversed; for the young and the adults of both sexes are grey and black

during the winter, the adults becoming white during the summer.[271] As

an instance of the second case, the young of the razor-bill (_Alca

torda_, Linn.), in an early state of plumage, are coloured like the

adults during the summer; and the young of the white-crowned sparrow of

North America (_Fringilla leucophrys_), as soon as fledged, have elegant

white stripes on their heads, which are lost by the young and the old

during the winter.[272] With respect to the third case, namely, that of

the young having an intermediate character between the summer and winter

adult plumages, Yarrell[273] insists that this occurs with many waders.

Lastly, in regard to the young differing greatly from both sexes in

their adult summer and winter plumages, this occurs with some herons and

egrets of North America and India,--the young alone being white.

I will make only a few remarks on these complicated cases. When the

young resemble the female in her summer dress, or the adults of both

sexes in their winter dress, the cases differ from those given under

Classes I. and III. only in the characters originally acquired by the

males during the breeding-season, having been limited in their

transmission to the corresponding season. When the adults have a

distinct summer and winter plumage, and the young differ from both, the

case is more difficult to understand. We may admit as probable that the

young have retained an ancient state of plumage; we can account through

sexual selection for the summer or nuptial plumage of the adults, but

how are we to account for their distinct winter plumage? If we could

admit that this plumage serves in all cases as a protection, its

acquirement would be a simple affair; but there seems no good reason for

this admission. It may be suggested that the widely different conditions

of life during the winter and summer have acted in a direct manner on

the plumage; this may have had some effect, but I have not much

confidence in so great a difference, as we sometimes see, between the

two plumages having been thus caused. A more probable explanation is,

that an ancient style of plumage, partially modified through the

transference of some characters from the summer plumage, has been

retained by the adults during the winter. Finally, all the cases in our

present class apparently depend on characters acquired by the adult

males, having been variously limited in their transmission according to

age, season, and sex; but it would not be worth while to attempt to

follow out these complex relations.

CLASS VI. _The young in their first plumage differ from each other

according to sex; the young males resembling more or less closely the

adult males, and the young females more or less closely the adult

females._--The cases in the present class, though occurring in various

groups, are not numerous; yet, if experience had not taught us to the

contrary, it seems the most natural thing that the young should at first

always resemble to a certain extent, and gradually become more and more

like, the adults of the same sex. The adult male blackcap (_Sylvia

atricapilla_) has a black head, that of the female being reddish-brown;

and I am informed by Mr. Blyth, that the young of both sexes can be

distinguished by this character even as nestlings. In the family of

thrushes an unusual number of similar cases have been noticed; the male

blackbird (_Turdus merula_) can be distinguished in the nest from the

female, as the main wing-feathers, which are not moulted so soon as the

body-feathers, retain a brownish tint until the second general

moult.[274] The two sexes of the mocking bird (_Turdus polyglottus_,

Linn.) differ very little from each other, yet the males can easily be

distinguished at a very early age from the females by shewing more pure

white.[275] The males of a forest-thrush and of a rock-thrush (viz.

_Orocetes erythrogastra_ and _Petrocincla cyanea_) have much of their

plumage of a fine blue, whilst the females are brown; and the nestling

males of both species have their main wing and tail-feathers edged with

blue, whilst those of the female are edged with brown.[276] So that the

very same feathers which in the young blackbird assume their mature

character and become black after the others, in these two species assume

this character and become blue before the others. The most probable view

with reference to these cases is that the males, differently from what

occurs in Class I., have transmitted their colours to their male

offspring at an earlier age than that at which they themselves first

acquired them; for if they had varied whilst quite young, they would

probably have transmitted all their characters to their offspring of

both sexes.[277]

In _Aithurus polytmus_ (one of the humming-birds) the male is splendidly

coloured black and green, and two of the tail-feathers are immensely

lengthened; the female has an ordinary tail and inconspicuous colours;

now the young males, instead of resembling the adult female, in

accordance with the common rule, begin from the first to assume the

colours proper to their sex, and their tail-feathers soon become

elongated. I owe this information to Mr. Gould, who has given me the

following more striking and as yet unpublished case. Two humming-birds

belonging to the genus Eustephanus, both beautifully coloured, inhabit

the small island of Juan Fernandez, and have always been ranked as

specifically distinct. But it has lately been ascertained that the one,

which is of a rich chesnut-brown colour with a golden-red head, is the

male, whilst the other, which is elegantly variegated with green and

white with a metallic-green head, is the female. Now the young from the

first resemble to a certain extent the adults of the corresponding sex,

the resemblance gradually becoming more and more complete.

In considering this last case, if as before we take the plumage of the

young as our guide, it would appear that both sexes have been

independently rendered beautiful; and not that the one sex has partially

transferred its beauty to the other. The male apparently has acquired

his bright colours through sexual selection in the same manner as, for

instance, the peacock or pheasant in our first class of cases; and the

female in the same manner as the female Rhynchaea or Turnix in our second

class of cases. But there is much difficulty in understanding how this

could have been effected at the same time with the two sexes of the same

species. Mr. Salvin states, as we have seen in the eighth chapter, that

with certain humming-birds the males greatly exceed in number the

females, whilst with other species inhabiting the same country the

females greatly exceed the males. If, then, we might assume that during

some former lengthened period the males of the Juan Fernandez species

had greatly exceeded the females in number, but that during another

lengthened period the females had greatly exceeded the males, we could

understand how the males at one time, and the females at another time,

might have been rendered beautiful by the selection of the

brighter-coloured individuals of either sex; both sexes transmitting

their characters to their young at a rather earlier age than usual.

Whether this is the true explanation I will not pretend to say; but the

case is too remarkable to be passed over without notice.

We have now seen in numerous instances under all six classes, that an

intimate relation exists between the plumage of the young and that of

the adults, either of one sex or both sexes. These relations are fairly

well explained on the principle that one sex--this being in the great

majority of cases the male--first acquired through variation and sexual

selection bright colours or other ornaments, and transmitted them in

various ways, in accordance with the recognised laws of inheritance. Why

variations have occurred at different periods of life, even sometimes

with the species of the same group, we do not know; but with respect to

the form of transmission, one important determining cause seems to have

been the age at which the variations first appeared.

From the principle of inheritance at corresponding ages, and from any

variations in colour which occurred in the males at an early age not

being then selected, on the contrary being often eliminated as

dangerous, whilst similar variations occurring at or near the period of

reproduction have been preserved, it follows that the plumage of the

young will often have been left unmodified, or but little modified. We

thus get some insight into the colouring of the progenitors of our

existing species. In a vast number of species in five out of our six

classes of cases, the adults of one sex or both are brightly coloured,

at least during the breeding-season, whilst the young are invariably

less brightly coloured than the adults, or are quite dull-coloured; for

no instance is known, as far as I can discover, of the young of

dull-coloured species displaying bright colours, or of the young of

brightly-coloured species being more brilliantly coloured than their

parents. In the fourth class, however, in which the young and the old

resemble each other, there are many species (though by no means all)

brightly-coloured, and as these form whole groups, we may infer that

their early progenitors were likewise brightly-coloured. With this

exception, if we look to the birds of the world, it appears that their

beauty has been greatly increased since that period, of which we have a

partial record in their immature plumage.

_On the Colour of the Plumage in relation to Protection._--It will have

been seen that I cannot follow Mr. Wallace in the belief that dull

colours when confined to the females have been in most cases specially

gained for the sake of protection. There can, however, be no doubt, as

formerly remarked, that both sexes of many birds have had their colours

modified for this purpose, so as to escape the notice of their enemies;

or, in some instances, so as to approach their prey unobserved, in the

same manner as owls have had their plumage rendered soft, that their

flight may not be overheard. Mr. Wallace remarks[278] that "it is only

in the tropics, among forests which never lose their foliage, that we

find whole groups of birds, whose chief colour is green." It will be

admitted by every one, who has ever tried, how difficult it is to

distinguish parrots in a leaf-covered tree. Nevertheless, we must

remember that many parrots are ornamented with crimson, blue, and orange

tints, which can hardly be protective. Woodpeckers are eminently

arboreal, but, besides green species, there are many black, and

black-and-white kinds--all the species being apparently exposed

to nearly the same dangers. It is therefore probable that

strongly-pronounced colours have been acquired by tree-haunting birds

through sexual selection, but that green tints have had an advantage

through natural selection over other colours for the sake of protection.

In regard to birds which live on the ground, everyone admits that they

are coloured so as to imitate the surrounding surface. How difficult it

is to see a partridge, snipe, woodcock, certain plovers, larks, and

nightjars when crouched on the ground. Animals inhabiting deserts offer

the most striking instances, for the bare surface affords no

concealment, and all the smaller quadrupeds, reptiles, and birds depend

for safety on their colours. As Mr. Tristram has remarked,[279] in

regard to the inhabitants of the Sahara, all are protected by their

"isabelline or sand-colour." Calling to my recollection the desert-birds

which I had seen in South America, as well as most of the ground-birds

in Great Britain, it appeared to me that both sexes in such cases are

generally coloured nearly alike. Accordingly I applied to Mr. Tristram,

with respect to the birds of the Sahara, and he has kindly given me the

following information. There are twenty-six species, belonging to

fifteen genera, which manifestly have had their plumage coloured in a

protective manner; and this colouring is all the more striking, as with

most of these birds it is different from that of their congeners. Both

sexes of thirteen out of the twenty-six species are coloured in the same

manner; but these belong to genera in which this rule commonly prevails,

so that they tell us nothing about the protective colours being the same

in both sexes of desert-birds. Of the other thirteen species, three

belong to genera in which the sexes usually differ from each other, yet

they have the sexes alike. In the remaining ten species, the male

differs from the female; but the difference is confined chiefly to the

under surface of the plumage, which is concealed when the bird crouches

on the ground; the head and back being of the same sand-coloured hue in

both sexes. So that in these ten species the upper surfaces of both

sexes have been acted on and rendered alike, through natural selection,

for the sake of protection; whilst the lower surfaces of the males alone

have been diversified through sexual selection, for the sake of

ornament. Here, as both sexes are equally well protected, we clearly see

that the females have not been prevented through natural selection from

inheriting the colours of their male parents: we must look to the law of

sexually limited transmission, as before explained.

In all parts of the world both sexes of many soft-billed birds,

especially those which frequent reeds or sedges, are obscurely coloured.

No doubt if their colours had been brilliant, they would have been much

more conspicuous to their enemies; but whether their dull tints have

been specially gained for the sake of protection seems, as far as I can

judge, rather doubtful. It is still more doubtful whether such dull

tints can have been gained for the sake of ornament. We must, however,

bear in mind that male birds, though dull-coloured, often differ much

from their females, as with the common sparrow, and this leads to the

belief that such colours have been gained through sexual selection, from

being attractive. Many of the soft-billed birds are songsters; and a

discussion in a former chapter should not be forgotten, in which it was

shewn that the best songsters are rarely ornamented with bright tints.

It would appear that female birds, as a general rule, have selected

their mates either for their sweet voices or gay colours, but not for

both charms combined. Some species which are manifestly coloured for the

sake of protection, such as the jack-snipe, woodcock, and nightjar, are

likewise marked and shaded, according to our standard of taste, with

extreme elegance. In such cases we may conclude that both natural and

sexual selection have acted conjointly for protection and ornament.

Whether any bird exists which does not possess some special attraction,

by which to charm the opposite sex, may be doubted. When both sexes are

so obscurely coloured, that it would be rash to assume the agency of

sexual selection, and when no direct evidence can be advanced shewing

that such colours serve as a protection, it is best to own complete

ignorance of the cause, or, which comes to nearly the same thing, to

attribute the result to the direct action of the conditions of life.

There are many birds both sexes of which are conspicuously, though not

brilliantly coloured, such as the numerous black, white, or piebald

species; and these colours, are probably the result of sexual selection.

With the common blackbird, capercailzie, black-cock, black Scoter-duck

(Oidemia), and even with one of the Birds of Paradise (_Lophorina

atra_), the males alone are black, whilst the females are brown or

mottled; and there can hardly be a doubt that blackness in these cases

has been a sexually selected character. Therefore it is in some degree

probable that the complete or partial blackness of both sexes in such

birds as crows, certain cockatoos, storks, and swans, and many marine

birds, is likewise the result of sexual selection, accompanied by equal

transmission to both sexes; for blackness can hardly serve in any case

as a protection. With several birds, in which the male alone is black,

and in others in which both sexes are black, the beak or skin about the

head is brightly coloured, and the contrast thus afforded adds greatly

to their beauty; we see this in the bright yellow beak of the male

blackbird, in the crimson skin over the eyes of the black-cock and

capercailzie, in the variously and brightly-coloured beak of the

Scoter-drake (Oidemia), in the red beak of the chough (_Corvus

graculus_, Linn.), of the black swan, and black stork. This leads me to

remark that it is not at all incredible that toucans may owe the

enormous size of their beaks to sexual selection, for the sake of

displaying the diversified and vivid stripes of colour, with which these

organs are ornamented.[280] The naked skin at the base of the beak and

round the eyes is likewise often brilliantly coloured; and Mr. Gould, in

speaking of one species,[281] says that the colours of the beak "are

doubtless in the finest and most brilliant state during the time of

pairing." There is no greater improbability in toucans being encumbered

with immense beaks, though rendered as light as possible by their

cancellated structure, for an object falsely appearing to us

unimportant, namely, the display of fine colours, than that the male

Argus pheasant and some other birds should be encumbered with plumes so

long as to impede their flight.

In the same manner, as the males alone of various species are black, the

females being dull-coloured; so in a few cases the males alone are

either wholly or partially white, as with the several Bell-birds of

South America (Chasmorhynchus), the Antarctic goose (_Bernicla

antarctica_), the silver pheasant, &c., whilst the females are brown or

obscurely mottled. Therefore, on the same principle as before, it is

probable that both sexes of many birds, such as white cockatoos, several

egrets with their beautiful plumes, certain ibises, gulls, terns, &c.,

have acquired their more or less completely white plumage through sexual

selection. The species which inhabit snowy regions of course come under

a different head. The white plumage of some of the above-named birds

appears in both sexes only when they are mature. This is likewise the

case with certain gannets, tropic-birds, &c., and with the snow-goose

(_Anser hyperboreus_). As the latter breeds on the "barren grounds,"

when not covered with snow, and as it migrates southward during the

winter, there is no reason to suppose that its snow-white adult plumage

serves as a protection. In the case of the _Anastomus oscitans_

previously alluded to, we have still better evidence that the white

plumage is a nuptial character, for it is developed only during the

summer; the young in their immature state, and the adults in their

winter dress, being grey and black. With many kinds of gulls (Larus),

the head and neck become pure white during the summer, being grey or

mottled during the winter and in the young state. On the other hand,

with the smaller gulls, or sea-mews (Gavia), and with some terns

(Sterna), exactly the reverse occurs; for the heads of the young birds

during the first year, and of the adults during the winter, are either

pure white, or much paler-coloured than during the breeding-season.

These latter cases offer another instance of the capricious manner in

which sexual selection appears often to have acted.[282]

The cause of aquatic birds having acquired a white plumage so much more

frequently than terrestrial birds, probably depends on their large size

and strong powers of flight, so that they can easily defend themselves

or escape from birds of prey, to which moreover they are not much

exposed. Consequently sexual selection has not here been interfered with

or guided for the sake of protection. No doubt, with birds which roam

over the open ocean, the males and females could find each other much

more easily when made conspicuous either by being perfectly white, or

intensely black; so that these colours may possibly serve the same end

as the call-notes of many land-birds. A white or black bird, when it

discovers and flies down to a carcase floating on the sea or cast up on

the beach, will be seen from a great distance, and will guide other

birds of the same and of distinct species, to the prey; but as this

would be a disadvantage to the first finders, the individuals which were

the whitest or blackest would not thus have procured more food than the

less strongly coloured individuals. Hence conspicuous colours cannot

have been gradually acquired for this purpose through natural

selection.[283]

As sexual selection depends on so fluctuating an element as taste, we

can understand how it is that within the same group of birds, with

habits of life nearly the same, there should exist white or nearly

white, as well as black, or nearly black species,--for instance, white

and black cockatoos, storks, ibises, swans, terns, and petrels. Piebald

birds likewise sometimes occur in the same groups, for instance, the

black-necked swan, certain terns, and the common magpie. That a strong

contrast in colour is agreeable to birds, we may conclude, by looking

through any large collection of specimens or series of coloured plates,

for the sexes frequently differ from each other in the male having the

pale parts of a purer white, and the variously coloured dark parts of

still darker tints than in the female.

It would even appear that mere novelty, or change for the sake of

change, has sometimes acted like a charm on female birds, in the same

manner as changes of fashion with us. The Duke of Argyll says,[284]--and

I am glad to have the unusual satisfaction of following for even a short

distance in his footsteps--"I am more and more convinced that variety,

mere variety, must be admitted to be an object and an aim in Nature." I

wish the Duke had explained what he here means by Nature. Is it meant

that the Creator of the universe ordained diversified results for His

own satisfaction, or for that of man? The former notion seems to me as

much wanting in due reverence as the latter in probability.

Capriciousness of taste in the birds themselves appears a more fitting

explanation. For example; the males of some parrots can hardly be said

to be more beautiful, at least according to our taste, than the females,

but they differ from them in such points, as the male having a

rose-coloured collar instead of, as in the female, "a bright emeraldine

narrow green collar;" or in the male having a black collar instead of "a

yellow demi-collar in front," with a pale roseate instead of a plum-blue

head.[285] As so many male birds have for their chief ornament elongated

tail-feathers or elongated crests, the shortened tail, formerly

described in the male of a humming-bird, and the shortened crest of the

male goosander almost seem like one of the many opposite changes of

fashion which we admire in our own dresses.

Some members of the heron family offer a still more curious case of

novelty in colouring having apparently been appreciated for the sake of

novelty. The young of the _Ardea asha_ are white, the adults being dark

slate-coloured; and not only the young, but the adults of the allied

_Buphus coromandus_ in their winter plumage are white, this colour

changing into a rich golden-buff during the breeding-season. It is

incredible that the young of these two species, as well as of some other

members of the same family,[286] should have been specially rendered

pure white and thus made conspicuous to their enemies; or that the

adults of one of these two species should have been specially rendered

white during the winter in a country which is never covered with snow.

On the other hand we have reason to believe that whiteness has been

gained by many birds as a sexual ornament. We may therefore conclude

that an early progenitor of the _Ardea asha_ and the _Buphus_ acquired a

white plumage for nuptial purposes, and transmitted this colour to their

young; so that the young and the old became white like certain existing

egrets; the whiteness having afterwards been retained by the young

whilst exchanged by the adults for more strongly pronounced tints. But

if we could look still further backwards in time to the still earlier

progenitors of these two species, we should probably see the adults

dark-coloured. I infer that this would be the case, from the analogy of

many other birds, which are dark whilst young, and when adult are white;

and more especially from the case of the _Ardea gularis_, the colours of

which are the reverse of those of _A. asha_, for the young are

dark-coloured and the adults white, the young having retained a former

state of plumage. It appears therefore that the progenitors in their

adult condition of the _Ardea asha_, the _Buphus_, and of some allies,

have undergone, during a long line of descent, the following changes of

colour: firstly a dark shade, secondly pure white, and thirdly, owing to

another change of fashion (if I may so express myself), their present

slaty, reddish, or golden-buff tints. These successive changes are

intelligible only on the principle of novelty having been admired by

birds for the sake of novelty.

_Summary of the Four Chapters on Birds._--Most male birds are highly

pugnacious during the breeding-season, and some possess weapons

especially adapted for fighting with their rivals. But the most

pugnacious and the best-armed males rarely or never depend for success

solely on their power to drive away or kill their rivals, but have

special means for charming the female. With some it is the power of

song, or of emitting strange cries, or of producing instrumental music,

and the males in consequence differ from the females in their vocal

organs, or in the structure of certain feathers. From the curiously

diversified means for producing various sounds we gain a high idea of

the importance of this means of courtship. Many birds endeavour to charm

the females by love-dances or antics, performed on the ground or in the

air, and sometimes at prepared places. But ornaments of many kinds, the

most brilliant tints, combs and wattles, beautiful plumes, elongated

feathers, top-knots, and so forth, are by far the commonest means. In

some cases mere novelty appears to have acted as a charm. The ornaments

of the males must be highly important to them, for they have been

acquired in not a few cases at the cost of increased danger from

enemies, and even at some loss of power in fighting with their rivals.

The males of very many species do not assume their ornamental dress

until they arrive at maturity, or they assume it only during the

breeding-season, or the tints then become more vivid. Certain ornamental

appendages become enlarged, turgid, and brightly-coloured during the

very act of courtship. The males display their charms with elaborate

care and to the best effect; and this is done in the presence of the

females. The courtship is sometimes a prolonged affair, and many males

and females congregate at an appointed place. To suppose that the

females do not appreciate the beauty of the males is to admit that their

splendid decorations, all their pomp and display, are useless; and this

is incredible. Birds have fine powers of discrimination, and in some few

instances it can be shewn that they have a taste for the beautiful. The

females, moreover, are known occasionally to exhibit a marked

preference or antipathy for certain individual males.

If it be admitted that the females prefer, or are unconsciously excited

by the more beautiful males, then the males would slowly but surely be

rendered more and more attractive through sexual selection. That it is

this sex which has been chiefly modified we may infer from the fact that

in almost every genus in which the sexes differ, the males differ much

more from each other than do the females; this is well shewn in certain

closely-allied representative species in which the females can hardly be

distinguished, whilst the males are quite distinct. Birds in a state of

nature offer individual differences which would amply suffice for the

work of sexual selection; but we have seen that they occasionally

present more strongly-marked variations which recur so frequently that

they would immediately be fixed, if they served to allure the female.

The laws of variation will have determined the nature of the initial

changes, and largely influenced the final result. The gradations, which

may be observed between the males of allied species, indicate the nature

of the steps which have been passed through, and explain in the most

interesting manner certain characters, such as the indented ocelli of

the tail-feathers of the peacock, and the wonderfully-shaded ocelli of

the wing-feathers of the Argus pheasant. It is evident that the

brilliant colours, top-knots, fine plumes, &c., of many male birds

cannot have been acquired as a protection; indeed they sometimes lead to

danger. That they are not due to the direct and definite action of the

conditions of life, we may feel assured, because the females have been

exposed to the same conditions, and yet often differ from the males to

an extreme degree. Although it is probable that changed conditions

acting during a lengthened period have produced some definite effect on

both sexes, the more important result will have been an increased

tendency to fluctuating variability or to augmented individual

differences; and such differences will have afforded an excellent

groundwork for the action of sexual selection.

The laws of inheritance, irrespectively of selection, appear to have

determined whether the characters acquired by the males for the sake of

ornament, for producing various sounds, and for fighting together, have

been transmitted to the males alone or to both sexes, either permanently

or periodically during certain seasons of the year. Why various

characters should sometimes have been transmitted in one way and

sometimes in another is, in most cases, not known; but the period of

variability seems often to have been the determining cause. When the two

sexes have inherited all characters in common they necessarily resemble

each other; but as the successive variations may be differently

transmitted, every possible gradation may be found, even within the same

genus, from the closest similarity to the widest dissimilarity between

the sexes. With many closely-allied species, following nearly the same

habits of life, the males have come to differ from each other chiefly

through the action of sexual selection; whilst the females have come to

differ chiefly from partaking in a greater or lesser degree of the

characters thus acquired by the males. The effects, moreover, of the

definite action of the conditions of life, will not have been masked in

the females, as in the case of the males, by the accumulation through

sexual selection of strongly-pronounced colours and other ornaments. The

individuals of both sexes, however affected, will have been kept at each

successive period nearly uniform by the free intercrossing of many

individuals.

With the species, in which the sexes differ in colour, it is possible

that at first there existed a tendency to transmit the successive

variations equally to both sexes; and that the females were prevented

from acquiring the bright colours of the males, on account of the danger

to which they would have been exposed during incubation. But it would

be, as far as I can see, an extremely difficult process to convert, by

means of natural selection, one form of transmission into another. On

the other hand there would not be the least difficulty in rendering a

female dull-coloured, the male being still kept bright-coloured, by the

selection of successive variations, which were from the first limited in

their transmission to the same sex. Whether the females of many species

have actually been thus modified, must at present remain doubtful. When,

through the law of the equal transmission of characters to both sexes,

the females have been rendered as conspicuously coloured as the males,

their instincts have often been modified, and they have been led to

build domed or concealed nests.

In one small and curious class of cases the characters and habits of the

two sexes have been completely transposed, for the females are larger,

stronger, more vociferous and brightly-coloured than their males. They

have, also, become so quarrelsome that they often fight together like

the males of the most pugnacious species. If, as seems probable, they

habitually drive away rival females, and by the display of their bright

colours or other charms endeavour to attract the males, we can

understand how it is that they have gradually been rendered, by means of

sexual selection and sexually-limited transmission, more beautiful than

the males--the latter being left unmodified or only slightly modified.

Whenever the law of inheritance at corresponding ages prevails, but not

that of sexually-limited transmission, then if the parents vary late in

life--and we know that this constantly occurs with our poultry, and

occasionally with other birds--the young will be left unaffected, whilst

the adults of both sexes will be modified. If both these laws of

inheritance prevail and either sex varies late in life, that sex alone

will be modified, the other sex and the young being left unaffected.

When variations in brightness or in other conspicuous characters occur

early in life, as no doubt often happens, they will not be acted on

through sexual selection until the period of reproduction arrives;

consequently they will be liable to be lost by the accidental deaths of

the young, and if dangerous will be eliminated through natural

selection. Thus we can understand how it is that variations arising late

in life have chiefly been preserved for the ornamentation and arming of

the males, the females and the young being left almost unaffected, and

therefore like each other. With species having a distinct summer and

winter plumage, the males of which either resemble or differ from the

females during both seasons or during the summer alone, the degrees and

kinds of resemblance between the young and the old are exceedingly

complex; and this complexity apparently depends on characters, first

acquired by the males, being transmitted in various ways and degrees, as

limited by age, sex, and season.

As the young of so many species have been but little modified in colour

and in other ornaments, we are enabled to form some judgment with

respect to the plumage of their early progenitors; and we may infer that

the beauty of our existing species, if we look to the whole class, has

been largely increased since that period of which the immature plumage

gives us an indirect record. Many birds, especially those which live

much on the ground, have undoubtedly been obscurely coloured for the

sake of protection. In some instances the upper exposed surface of the

plumage has been thus coloured in both sexes, whilst the lower surface

in the males alone has been variously ornamented through sexual

selection. Finally, from the facts given in these four chapters, we may

conclude that weapons for battle, organs for producing sound, ornaments

of many kinds, bright and conspicuous colours, have generally been

acquired by the males through variation and sexual selection, and have

been transmitted in various ways according to the several laws of

inheritance--the females and the young being left comparatively but

little modified.[287]

CHAPTER XVII.

SECONDARY SEXUAL CHARACTERS OF MAMMALS.

The law of battle--Special weapons, confined to the

males--Cause of absence of weapons in the female--Weapons

common to both sexes, yet primarily acquired by the

male--Other uses of such weapons--Their high

importance--Greater size of the male--Means of defence--On the

preference shewn by either sex in the pairing of quadrupeds.

With mammals the male appears to win the female much more through the

law of battle than through the display of his charms. The most timid

animals, not provided with any special weapons for fighting, engage in

desperate conflicts during the season of love. Two male hares have been

seen to fight together until one was killed; male moles often fight, and

sometimes with fatal results; male squirrels "engage in frequent

contests, and often wound each other severely;" as do male beavers, so

that "hardly a skin is without scars."[288] I observed the same fact

with the hides of the guanacoes in Patagonia; and on one occasion

several were so absorbed in fighting that they fearlessly rushed close

by me. Livingstone speaks of the males of the many animals in Southern

Africa as almost invariably shewing the scars received in former

contests.

The law of battle prevails with aquatic as with terrestrial mammals. It

is notorious how desperately male seals fight, both with their teeth and

claws, during the breeding-season; and their hides are likewise often

covered with scars. Male sperm-whales are very jealous at this season;

and in their battles "they often lock their jaws together, and turn on

their sides and twist about;" so that it is believed by some naturalists

that the frequently deformed state of their lower jaws is caused by

these struggles.[289]

All male animals which are furnished with special weapons for fighting,

are well known to engage in fierce battles. The courage and the

desperate conflicts of stags have often been described; their skeletons

have been found in various parts of the world, with the horns

inextricably locked together, shewing how miserably the victor and

vanquished had perished.[290] No animal in the world is so dangerous as

an elephant in must. Lord Tankerville has given me a graphic description

of the battles between the wild bulls in Chillingham Park, the

descendants, degenerated in size but not in courage, of the gigantic

_Bos primigenius_. In 1861 several contended for mastery; and it was

observed that two of the younger bulls attacked in concert the old

leader of the herd, overthrew and disabled him, so that he was believed

by the keepers to be lying mortally wounded in a neighbouring wood. But

a few days afterwards one of the young bulls singly approached the wood;

and then the "monarch of the chase," who had been lashing himself up

for vengeance, came out and, in a short time killed his antagonist. He

then quietly joined the herd, and long held undisputed sway. Admiral Sir

B. J. Sulivan informs me that when he resided in the Falkland Islands he

imported a young English stallion, which, with eight mares, frequented

the hills near Port William. On these hills there were two wild

stallions, each with a small troop of mares; "and it is certain that

these stallions would never have approached each other without fighting.

Both had tried singly to fight the English horse and drive away his

mares, but had failed. One day they came in _together_ and attacked him.

This was seen by the capitan who had charge of the horses, and who, on

riding to the spot, found one of the two stallions engaged with the

English horse, whilst the other was driving away the mares, and had

already separated four from the rest. The capitan settled the matter by

driving the whole party into the corral, for the wild stallions would

not leave the mares."

Male animals already provided with efficient cutting or tearing teeth

for the ordinary purposes of life, as in the carnivora, insectivora, and

rodents, are seldom furnished with weapons especially adapted for

fighting with their rivals. The case is very different with the males of

many other animals. We see this in the horns of stags and of certain

kinds of antelopes in which the females are hornless. With many animals

the canine teeth in the upper or lower jaw, or in both, are much larger

in the males than in the females; or are absent in the latter, with the

exception sometimes of a hidden rudiment. Certain antelopes, the

musk-deer, camel, horse, boar, various apes, seals, and the walrus,

offer instances of these several cases. In the females of the walrus

the tusks are sometimes quite absent.[291] In the male elephant of India

and in the male dugong[292] the upper incisors form offensive weapons.

In the male narwhal one alone of the upper teeth is developed into the

well-known, spirally-twisted, so called horn, which is sometimes from

nine to ten feet in length. It is believed that the males use these

horns for fighting together; for "an unbroken one can rarely be got, and

occasionally one may be found with the point of another jammed into the

broken place."[293] The tooth on the opposite side of the head in the

male consists of a rudiment about ten inches in length, which is

embedded in the jaw. It is not, however, very uncommon to find

double-horned male narwhals in which both teeth are well developed. In

the females both teeth are rudimentary. The male cachalot has a larger

head than that of the female, and it no doubt aids these animals in

their aquatic battles. Lastly, the adult male ornithorhynchus is

provided with a remarkable apparatus, namely a spur on the fore-leg,

closely resembling the poison-fang of a venomous snake; its use is not

known, but we may suspect that it serves as a weapon of offence.[294] It

is represented by a mere rudiment in the female.

When the males are provided with weapons which the females do not

possess, there can hardly be a doubt that they are used for fighting

with other males, and that they have been acquired through sexual

selection.

It is not probable, at least in most cases, that the females have

actually been saved from acquiring such weapons, owing to their being

useless and superfluous, or in some way injurious. On the contrary, as

they are often used by the males of many animals for various purposes,

more especially as a defence against their enemies, it is a surprising

fact that they are so poorly developed or quite absent in the females.

No doubt with female deer the development during each recurrent season

of great branching horns, and with female elephants the development of

immense tusks, would have been a great waste of vital power, on the

admission that they were of no use to the females. Consequently

variations in the size of these organs, leading to their suppression,

would have come under the control of natural selection, and if limited

in their transmission to the female offspring would not have interfered

with their development through sexual selection in the males. But how on

this view can we explain the presence of horns in the females of certain

antelopes, and of tusks in the females of many animals, which are only

of slightly less size than in the males? The explanation in almost all

cases must, I believe, be sought in the laws of transmission.

As the reindeer is the single species in the whole family of Deer in

which the female is furnished with horns, though somewhat smaller,

thinner, and less branched than in the male, it might naturally be

thought that they must be of some special use to her. There is, however,

some evidence opposed to this view. The female retains her horns from

the time when they are fully developed, namely in September, throughout

the winter, until May, when she brings forth her young; whilst the male

casts his horns much earlier, towards the end of November. As both sexes

have the same requirements and follow the same habits of life, and as

the male sheds his horns during the winter, it is very improbable that

they can be of any special service to the female at this season, which

includes the larger proportion of the time during which she bears horns.

Nor is it probable that she can have inherited horns from some ancient

progenitor of the whole family of deer, for, from the fact of the males

alone of so many species in all quarters of the globe possessing horns,

we may conclude that this was the primordial character of the group.

Hence it appears that horns must have been transferred from the male to

the female at a period subsequent to the divergence of the various

species from a common stock; but that this was not effected for the sake

of giving her any special advantage.[295]

We know that the horns are developed at a most unusually early age in

the reindeer; but what the cause of this may have been is not known. The

effect, however, has apparently been the transference of the horns to

both sexes. It is intelligible on the hypothesis of pangenesis, that a

very slight change in the constitution of the male, either in the

tissues of the forehead or in the gemmules of the horns, might lead to

their early development; and as the young of both sexes have nearly the

same constitution before the period of reproduction, the horns, if

developed at an early age in the male, would tend to be developed

equally in both sexes. In support of this view, we should bear in mind

that the horns are always transmitted through the female, and that she

has a latent capacity for their development, as we see in old or

diseased females.[296] Moreover the females of some other species of

deer either normally or occasionally exhibit rudiments of horns; thus

the female of _Cervulus moschatus_ has "bristly tufts, ending in a knob,

instead of a horn;" and "in most specimens of the female Wapiti (_Cervus

Canadensis_) there is a sharp bony protuberance in the place of the

horn."[297] From these several considerations we may conclude that the

possession of fairly well-developed horns by the female reindeer, is due

to the males having first acquired them as weapons for fighting with

other males; and secondarily to their development from some unknown

cause at an unusually early age in the males, and their consequent

transmission to both sexes.

Turning to the sheath-horned ruminants: with antelopes a graduated

series can be formed, beginning with the species, the females of which

are completely destitute of horns--passing to those which have horns so

small as to be almost rudimentary, as in _Antilocapra Americana_--to

those which have fairly well-developed horns, but manifestly smaller and

thinner than in the male, and sometimes of a different shape,[298] and

ending with those in which both sexes have horns of equal size. As with

the reindeer, so with antelopes there exists a relation between the

period of the development of the horns and their transmission to one or

both sexes; it is therefore probable that their presence or absence in

the females of some species, and their more or less perfect condition in

the females of other species, depend, not on their being of some special

use, but simply on the form of inheritance which has prevailed. It

accords with this view that even in the same restricted genus both sexes

of some species, and the males alone of other species, are thus

provided. It is a remarkable fact that, although the females of

_Antilope bezoartica_ are normally destitute of horns, Mr. Blyth has

seen no less than three females thus furnished; and there was no reason

to suppose that they were old or diseased. The males of this species

have long straight spirated horns, nearly parallel to each other, and

directed backwards. Those of the female, when present, are very

different in shape, for they are not spirated, and spreading widely bend

round, so that their points are directed forwards. It is a still more

remarkable fact that in the castrated male, as Mr. Blyth informs me, the

horns are of the same peculiar shape as in the female, but longer and

thicker. In all cases the differences between the horns of the males and

females, and of castrated and entire males, probably depend on various

causes,--on the more or less complete transference of male characters to

the females,--on the former state of the progenitors of the

species,--and partly perhaps on the horns being differently nourished,

in nearly the same manner as the spurs of the domestic cock, when

inserted into the comb or other parts of the body, assume various

abnormal forms from being differently nourished.

In all the wild species of goats and sheep the horns are larger in the

male than in the female, and are sometimes quite absent in the

latter.[299] In several domestic breeds of the sheep and goat, the

males alone are furnished with horns; and it is a significant fact, that

in one such breed of sheep on the Guinea coast, the horns are not

developed, as Mr. Winwood Reade informs me, in the castrated male; so

that they are affected in this respect like the horns of stags. In some

breeds, as in that of N. Wales, in which both sexes are properly horned,

the ewes are very liable to be hornless. In these same sheep, as I have

been informed by a trustworthy witness who purposely inspected a flock

during the lambing-season, the horns at birth are generally more fully

developed in the male than in the female. With the adult musk-ox

(_Ovibos moschatus_) the horns of the male are larger than those of the

female, and in the latter the bases do not touch.[300] In regard to

ordinary cattle Mr. Blyth remarks: "In most of the wild bovine animals

the horns are both longer and thicker in the bull than in the cow, and

in the cow-banteng (_Bos sondaicus_) the horns are remarkably small, and

inclined much backwards. In the domestic races of cattle, both of the

humped and humpless types, the horns are short and thick in the bull,

longer and more slender in the cow and ox; and in the Indian buffalo,

they are shorter and thicker in the bull, longer and more slender in the

cow. In the wild gaour (_B. gaurus_) the horns are mostly both longer

and thicker in the bull than in the cow."[301] Hence with most

sheath-horned ruminants the horns of the male are either longer or

stronger than those of the female. With the _Rhinoceros simus_, as I may

here add, the horns of the female are generally longer but less powerful

than in the male; and in some other species of rhinoceros they are said

to be shorter in the female.[302] From these various facts we may

conclude that horns of all kinds, even when they are equally developed

in both sexes, were primarily acquired by the males in order to conquer

other males, and have been transferred more or less completely to the

female, in relation to the force of the equal form of inheritance.

The tusks of the elephant, in the different species or races, differ

according to sex, in nearly the same manner as the horns of ruminants.

In India and Malacca the males alone are provided with well-developed

tusks. The elephant of Ceylon is considered by most naturalists as a

distinct race, but by some as a distinct species, and here "not one in a

hundred is found with tusks, the few that possess them being exclusively

males."[303] The African elephant is undoubtedly distinct, and the

female has large, well-developed tusks, though not so large as those of

the male. These differences in the tusks of the several races and

species of elephants--the great variability of the horns of deer, as

notably in the wild reindeer--the occasional presence of horns in the

female _Antilope bezoartica_--the presence of two tusks in some few male

narwhals--the complete absence of tusks in some female walruses;--are

all instances of the extreme variability of secondary sexual characters,

and of their extreme liability to differ in closely-allied forms.

Although tusks and horns appear in all cases to have been primarily

developed as sexual weapons, they often serve for other purposes. The

elephant uses his tusks in attacking the tiger; according to Bruce, he

scores the trunks of trees until they can be easily thrown down, and he

likewise thus extracts the farinaceous cores of palms; in Africa he

often uses one tusk, this being always the same, to probe the ground and

thus to ascertain whether it will bear his weight. The common bull

defends the herd with his horns; and the elk in Sweden has been known,

according to Lloyd, to strike a wolf dead with a single blow of his

great horns. Many similar facts could be given. One of the most curious

secondary uses to which the horns of any animal are occasionally put, is

that observed by Captain Hutton[304] with the wild goat (_Capra

aegagrus_) of the Himalayas, and as it is said with the ibex, namely,

that when the male accidentally falls from a height he bends inwards his

head, and, by alighting on his massive horns, breaks the shock. The

female cannot thus use her horns, which are smaller, but from her more

quiet disposition she does not so much need this strange kind of shield.

Each male animal uses his weapons in his own peculiar fashion. The

common ram makes a charge and butts with such force with the bases of

his horns, that I have seen a powerful man knocked over as easily as a

child. Goats and certain species of sheep, for instance the _Ovis

cycloceros_ of Afghanistan,[305] rear on their hind legs, and then not

only butt, but "make a cut down and a jerk up, with the ribbed front of

their scimitar-shaped horn, as with a sabre. When the _O. cycloceros_

attacked a large domestic ram, who was a noted bruiser, he conquered him

by the sheer novelty of his mode of fighting, always closing at once

with his adversary, and catching him across the face and nose with a

sharp drawing jerk of his head, and then bounding out of the way before

the blow could be returned." In Pembrokeshire a male goat, the master of

a flock which during several generations had run wild, was known to have

killed several other males in single combat; this goat possessed

enormous horns, measuring 39 inches in a straight line from tip to tip.

The common bull, as every one knows, gores and tosses his opponent; but

the Italian buffalo is said never to use his horns, he gives a

tremendous blow with his convex forehead, and then tramples on his

fallen enemy with his knees--an instinct which the common bull does not

possess.[306] Hence a dog who pins a buffalo by the nose is immediately

crushed. We must, however, remember that the Italian buffalo has long

been domesticated, and it is by no means certain that the wild

parent-form had similarly shaped horns. Mr. Bartlett informs me that

when a female Cape buffalo (_Bubalus caffer_) was turned into an

enclosure with a bull of the same species, she attacked him, and he in

return pushed her about with great violence. But it was manifest to Mr.

Bartlett that had not the bull shewn dignified forbearance, he could

easily have killed her by a single lateral thrust with his immense

horns. The giraffe uses his short hair-covered horns, which are rather

longer in the male than in the female, in a curious manner; for with his

long neck he swings his head to either side, almost upside down, with

such force, that I have seen a hard plank deeply indented by a single

blow.

[Illustration: Fig. 61. Oryx leucoryx, male (from the Knowsley

Menagerie).]

With antelopes it is sometimes difficult to imagine how they can

possibly use their curiously-shaped horns; thus the spring-boc (_Ant.

euchore_) has rather short upright horns, with the sharp points bent

inwards almost at a right angle, so as to face each other; Mr. Bartlett

does not know how they are used, but suggests that they would inflict a

fearful wound down each side of the face of an antagonist. The

slightly-curved horns of the _Oryx leucoryx_ (fig. 61) are directed

backwards, and are of such length that their points reach beyond the

middle of the back, over which they stand in an almost parallel line.

Thus they seem singularly ill-fitted for fighting; but Mr. Bartlett

informs me that when two of these animals prepare for battle, they kneel

down, with their heads between their front legs, and in this attitude

the horns stand nearly parallel and close to the ground, with the points

directed forwards and a little upwards. The combatants then gradually

approach each other and endeavour to get the upturned points under each

other's bodies; if one succeeds in doing this, he suddenly springs up,

throwing up his head at the same time, and can thus wound or perhaps

even transfix his antagonist. Both animals always kneel down so as to

guard as far as possible against this manoeuvre. It has been recorded

that one of these antelopes has used his horns with effect even against

a lion; yet from being forced to place his head between the forelegs in

order to bring the points of the horns forward, he would generally be

under a great disadvantage when attacked by any other animal. It is,

therefore, not probable that the horns have been modified into their

present great length and peculiar position, as a protection against

beasts of prey. We can, however, see that as soon as some ancient male

progenitor of the Oryx acquired moderately long horns, directed a little

backwards, he would be compelled in his battles with rival males to bend

his head somewhat inwards or downwards, as is now done by certain stags;

and it is not improbable that he might have acquired the habit of at

first occasionally and afterwards of regularly kneeling down. In this

case it is almost certain that the males which possessed the longest

horns would have had a great advantage over others with shorter horns;

and then the horns would gradually have been rendered longer and longer,

through sexual selection, until they acquired their present

extraordinary length and position.

With stags of many kinds the branching of the horns offers a curious

case of difficulty; for certainly a single straight point would inflict

a much more serious wound than several diverging points. In Sir Philip

Egerton's museum there is a horn of the red-deer (_Cervus elaphus_)

thirty inches in length, with "not fewer than fifteen snags or

branches;" and at Moritzburg there is still preserved a pair of antlers

of a red-deer, shot in 1699 by Frederick I., each of which bears the

astonishing number of thirty-three branches. Richardson figures a pair

of antlers of the wild reindeer with twenty-nine points.[307] From the

manner in which the horns are branched, and more especially from deer

being known occasionally to fight together by kicking with their

fore-feet,[308] M. Bailly actually came to the conclusion that their

horns were more injurious than useful to them! But this author overlooks

the pitched battles between rival males. As I felt much perplexed about

the use or advantage of the branches, I applied to Mr. McNeill of

Colinsay, who has long and carefully observed the habits of red-deer,

and he informs me that he has never seen some of the branches brought

into action, but that the brow-antlers, from inclining downwards, are a

great protection to the forehead, and their points are likewise used in

attack. Sir Philip Egerton also informs me in regard both to red-deer

and fallow-deer, that when they fight they suddenly dash together, and

getting their horns fixed against each other's bodies a desperate

struggle ensues. When one is at last forced to yield and turn round, the

victor endeavours to plunge his brow-antlers into his defeated foe. It

thus appears that the upper branches are used chiefly or exclusively for

pushing and fencing. Nevertheless with some species the upper branches

are used as weapons of offence; when a man was attacked by a Wapiti

deer (_Cervus Canadensis_) in Judge Caton's park in Ottawa, and several

men tried to rescue him, the stag "never raised his head from the

ground; in fact he kept his face almost flat on the ground, with his

nose nearly between his fore-feet, except when he rolled his head to one

side to take a new observation preparatory to a plunge." In this

position the terminal points of the horns were directed against his

adversaries. "In rolling his head he necessarily raised it somewhat,

because his antlers were so long that he could not roll his head without

raising them on one side, while on the other side they touched the

ground." The stag by this procedure gradually drove the party of

rescuers backwards, to a distance of 150 or 200 feet; and the attacked

man was killed.[309]

Although the horns of stags are efficient weapons, there can, I think,

be no doubt that a single point would have been much more dangerous than

a branched antler; and Judge Caton, who has had large experience with

deer, fully concurs in this conclusion. Nor do the branching horns,

though highly important as a means of defence against rival stags,

appear perfectly well adapted for this purpose, as they are liable to

become interlocked. The suspicion has therefore crossed my mind that

they may serve partly as ornaments. That the branched antlers of stags,

as well as the elegant lyrated horns of certain antelopes, with their

graceful double curvature, (fig. 62), are ornamental in our eyes, no one

will dispute. If, then, the horns, like the splendid accoutrements of

the knights of old, add to the noble appearance of stags and antelopes,

they may have been partly modified for this purpose, though mainly for

actual service in battle; but I have no evidence in favour of this

belief.

[Illustration: Fig. 62. Strepsiceros Kudu (from Andrew Smith's 'Zoology

of South Africa').]

An interesting case has lately been published, from which it appears

that the horns of a deer in one district in the United States are now

being modified through sexual and natural selection. A writer in an

excellent American Journal[310] says, that he has hunted for the last

twenty-one years in the Adirondacks, where the _Cervus Virginianus_

abounds. About fourteen years ago he first heard of _spike-horn bucks_.

These became from year to year more common; about five years ago he shot

one, and subsequently another, and now they are frequently killed. "The

spike-horn differs greatly from the common antler of the _C.

Virginianus_. It consists of a single spike, more slender than the

antler, and scarcely half so long, projecting forward from the brow, and

terminating in a very sharp point. It gives a considerable advantage to

its possessor over the common buck. Besides enabling him to run more

swiftly through the thick woods and underbrush (every hunter knows that

does and yearling bucks run much more rapidly than the large bucks when

armed with their cumbrous antlers), the spike-horn is a more effective

weapon than the common antler. With this advantage the spike-horn bucks

are gaining upon the common bucks, and may, in time, entirely supersede

them in the Adirondacks. Undoubtedly the first spike-horn buck was

merely an accidental freak of nature. But his spike-horns gave him an

advantage, and enabled him to propagate his peculiarity. His

descendants, having a like advantage, have propagated the peculiarity in

a constantly increasing ratio, till they are slowly crowding the

antlered deer from the region they inhabit."

Male quadrupeds which are furnished with tusks use them in various ways,

as in the case of horns. The boar strikes laterally and upwards; the

musk-deer with serious effect downwards.[311] The walrus, though having

so short a neck and so unwieldy a body, "can strike either upwards, or

downwards, or sideways, with equal dexterity."[312] The Indian elephant

fights, as I was informed by the late Dr. Falconer, in a different

manner according to the position and curvature of his tusks. When they

are directed forwards and upwards he is able to fling a tiger to a great

distance--it is said to even thirty feet; when they are short and turned

downwards he endeavours suddenly to pin the tiger to the ground, and in

consequence is dangerous to the rider, who is liable to be jerked off

the hoodah.[313]

Very few male quadrupeds possess weapons of two distinct kinds specially

adapted for fighting with rival males. The male muntjac-deer

(_Cervulus_), however, offers an exception, as he is provided with horns

and exserted canine teeth. But one form of weapon, has often been

replaced in the course of ages by another form, as we may infer from

what follows. With ruminants the development of horns generally stands

in an inverse relation with that of even moderately well-developed

canine teeth. Thus camels, guanacoes, chevrotains and musk-deer, are

hornless, and they have efficient canines; these teeth being "always of

smaller size in the females than in the males." The Camelidae have in

their upper jaws, in addition to their true canines, a pair of

canine-shaped incisors.[314] Male deer and antelopes, on the other hand,

possess horns, and they rarely have canine teeth; and these when present

are always of small size, so that it is doubtful whether they are of

any service in their battles. With _Antilope montana_ they exist only as

rudiments in the young male, disappearing as he grows old; and they are

absent in the female at all ages; but the females of certain other

antelopes and deer have been known occasionally to exhibit rudiments of

these teeth.[315] Stallions have small canine teeth, which are either

quite absent or rudimentary in the mare; but they do not appear to be

used in fighting, for stallions bite with their incisors, and do not

open their mouths widely like camels and guanacoes. Whenever the adult

male possesses canines now in an inefficient state, whilst the female

has either none or mere rudiments, we may conclude that the early male

progenitor of the species was provided with efficient canines, which had

been partially transferred to the females. The reduction of these teeth

in the males seems to have followed from some change in their manner of

fighting, often caused (but not in the case of the horse) by the

development of new weapons.

Tusks and horns are manifestly of high importance to their possessors,

for their development consumes much organised matter. A single tusk of

the Asiatic elephant,--one of the extinct woolly species,--and of the

African elephant, have been known to weigh respectively 150, 160, and

180 pounds; and even greater weights have been assigned by some

authors.[316] With deer, in which the horns are periodically renewed,

the drain on the constitution must be greater; the horns, for instance,

of the moose weigh from fifty to sixty pounds, and those of the extinct

Irish elk from sixty to seventy pounds,--the skull of the latter

weighing on an average only five and a quarter pounds. With sheep,

although the horns are not periodically renewed, yet their development,

in the opinion of many agriculturists, entails a sensible loss to the

breeder. Stags, moreover, in escaping from beasts of prey are loaded

with an additional weight for the race, and are greatly retarded in

passing through a woody country. The moose, for instance, with horns

extending five and a half feet from tip to tip, although so skilful in

their use that he will not touch or break a dead twig when walking

quietly, cannot act so dexterously whilst rushing away from a pack of

wolves. "During his progress he holds his nose up, so as to lay the

horns horizontally back; and in this attitude cannot see the ground

distinctly."[317] The tips of the horns of the great Irish elk were

actually eight feet apart! Whilst the horns are covered with velvet,

which lasts with the red-deer for about twelve weeks, they are extremely

sensitive to a blow; so that in Germany the stags at this time change

their habits to a certain extent, and avoid dense forests, frequenting

young woods and low thickets.[318] These facts remind us, that male

birds have acquired ornamental plumes at the cost of retarded flight,

and other ornaments at the cost of some loss of power in their battles

with rival males.

With quadrupeds, when, as is often the case, the sexes differ in size,

the males are, I believe, always larger and stronger. This holds good in

a marked manner, as I am informed by Mr. Gould, with the marsupials of

Australia, the males of which appear to continue growing until an

unusually late age. But the most extraordinary case is that of one of

the seals (_Callorhinus ursinus_), a full-grown female weighing less

than one-sixth of a full-grown male.[319] The greater strength of the

male is invariably displayed, as Hunter long ago remarked,[320] in those

parts of the body which are brought into action in fighting with rival

males,--for instance, in the massive neck of the bull. Male quadrupeds

are also more courageous and pugnacious than the females. There can be

little doubt that these characters have been gained, partly through

sexual selection, owing to a long series of victories by the stronger

and more courageous males over the weaker, and partly through the

inherited effects of use. It is probable that the successive variations

in strength, size, and courage, whether due to so-called spontaneous

variability or to the effects of use, by the accumulation of which male

quadrupeds have acquired these characteristic qualities, occurred rather

late in life, and were consequently to a large extent limited in their

transmission to the same sex.

Under this point of view I was anxious to obtain information in regard

to the Scotch deerhound, the sexes of which differ more in size than

those of any other breed (though blood-hounds differ considerably), or

than in any wild canine species known to me.

Accordingly, I applied to Mr. Cupples, a well-known breeder of these

dogs, who has weighed and measured many of his own dogs, and who, with

great kindness, has collected for me the following facts from various

sources. Superior male dogs, measured at the shoulder, range from

twenty-eight inches, which is low, to thirty-three, or even thirty-four

inches in height; and in weight from eighty pounds, which is low, to

120, or even more pounds. The females range in height from twenty-three

to twenty-seven, or even to twenty-eight inches; and in weight from

fifty to seventy, or even eighty pounds.[321] Mr. Cupples concludes that

from ninety-five to one hundred pounds for the male, and seventy for the

female, would be a safe average; but there is reason to believe that

formerly both sexes attained a greater weight. Mr. Cupples has weighed

puppies when a fortnight old; in one litter the average weight of four

males exceeded that of two females by six and a half ounces; in another

litter the average weight of four males exceeded that of one female by

less than one ounce; the same males, when three weeks old, exceeded the

female by seven and a half ounces, and at the age of six weeks by nearly

fourteen ounces. Mr. Wright of Yeldersley House, in a letter to Mr.

Cupples, says: "I have taken notes on the sizes and weights of puppies

of many litters, and as far as my experience goes, dog-puppies as a rule

differ very little from bitches till they arrive at about five or six

months old; and then the dogs begin to increase, gaining upon the

bitches both in weight and size. At birth, and for several weeks

afterwards, a bitch-puppy will occasionally be larger than any of the

dogs, but they are invariably beaten by them later." Mr. McNeill, of

Colinsay, concludes that "the males do not attain their full growth till

over two years old, though the females attain it sooner." According to

Mr. Cupples' experience, male dogs go on growing in stature till they

are from twelve to eighteen months old, and in weight till from eighteen

to twenty-four months old; whilst the females cease increasing in

stature at the age of from nine to fourteen or fifteen months, and in

weight at the age of from twelve to fifteen months. From these various

statements it is clear that the full difference in size between the male

and female Scotch deerhound is not acquired until rather late in life.

The males are almost exclusively used for coursing, for, as Mr. McNeill

informs me, the females have not sufficient strength and weight to pull

down a full-grown deer. From the names used in old legends, it appears,

as I hear from Mr. Cupples, that at a very ancient period the males were

the most celebrated, the females being mentioned only as the mothers of

famous dogs. Hence during many generations, it is the male which has

been chiefly tested for strength, size, speed, and courage, and the best

will have been bred from. As, however, the males do not attain their

full dimensions until a rather late period in life, they will have

tended, in accordance with the law often indicated, to transmit their

characters to their male offspring alone; and thus the great inequality

in size between the sexes of the Scotch deerhound may probably be

accounted for.

[Illustration: Fig. 63. Head of common wild boar, in prime of life (from

Brehm).]

The males of some few quadrupeds possess organs or parts developed

solely as a means of defence against the attacks of other males. Some

kinds of deer use, as we have seen, the upper branches of their horns

chiefly or exclusively for defending themselves; and the Oryx antelope,

as I am informed by Mr. Bartlett, fences most skilfully with his long,

gently curved horns; but these are likewise used as organs of offence.

Rhinoceroses, as the same observer remarks, in fighting parry each

other's sidelong blows with their horns, which loudly clatter together,

as do the tusks of boars. Although wild boars fight desperately

together, they seldom, according to Brehm, receive fatal blows, as these

fall on each other's tusks, or on the layer of gristly skin covering the

shoulder, which the German hunters call the shield; and here we have a

part specially modified for defence. With boars in the prime of life

(see fig. 63) the tusks in the lower jaw are used for fighting but they

become in old age, as Brehm states, so much curved inwards and upwards,

over the snout, that they can no longer be thus used. They may, however,

still continue to serve, and even in a still more effective manner, as a

means of defence. In compensation for the loss of the lower tusks as

weapons of offence, those in the upper jaw, which always project a

little laterally, increase so much in length during old age, and curve

so much upwards, that they can be used as a means of attack.

Nevertheless an old boar is not so dangerous to man as one at the age

of six or seven years.[322]

[Illustration: Fig 64. Skull of the Babirusa Pig (from Wallace's 'Malay

Archipelago')]

In the full-grown male Babirusa pig of Celebes (fig. 64), the lower

tusks are formidable weapons, like those of the European boar in the

prime of life, whilst the upper tusks are so long and have their points

so much curled inwards, sometimes even touching the forehead, that they

are utterly useless as weapons of attack. They more nearly resemble

horns than teeth, and are so manifestly useless as teeth that the animal

was formerly supposed to rest his head by hooking them on to a branch.

Their convex surfaces would, however, if the head were held a little

laterally, serve as an excellent guard; and hence, perhaps it is that in

old animals they "are generally broken off, as if by fighting."[323]

Here, then, we have the curious case of the upper tusks of the Babirusa

regularly assuming during the prime of life, a structure which

apparently renders them fitted only for defence; whilst in the European

boar the lower and opposite tusks assume in a less degree and only

during old age nearly the same form, and then serve in like manner

solely for defence.

[Illustration: Fig. 65. Head of Aethiopian Wart-hog, from 'Proc. Zool.

Soc.' 1869. (I now find that this drawing represents the head of a

female, but it serves to shew, on a reduced scale, the characters of the

male.)]

In the wart-hog (_Phacochoerus aethiopicus_, fig. 65) the tusks in the

upper jaw of the male curve upwards during the prime of life, and from

being pointed, serve as formidable weapons. The tusks in the lower jaw

are sharper than those in the upper, but from their shortness it seems

hardly possible that they can be used as weapons of attack. They must,

however, greatly strengthen those in the upper jaw, from being ground

so as to fit closely against their bases. Neither the upper nor the

lower tusks appear to have been specially modified to act as guards,

though, no doubt, they are thus used to a certain extent. But the

wart-hog is not destitute of other special means of protection, for

there exists, on each side of the face, beneath the eyes, a rather

stiff, yet flexible, cartilaginous, oblong pad (fig. 65), which projects

two or three inches outwards; and it appeared to Mr. Bartlett and

myself, when viewing the living animal, that these pads, when struck

from beneath by the tusks of an opponent, would be turned upwards, and

would thus protect in an admirable manner the somewhat prominent eyes.

These boars, as I may add on the authority of Mr. Bartlett, when

fighting together, stand directly face to face.

Lastly, the African river-hog (_Potamochoerus penicillatus_) has a hard

cartilaginous knob on each side of the face beneath the eyes, which

answers to the flexible pad of the wart-hog; it has also two bony

prominences on the upper jaw above the nostrils. A boar of this species

in the Zoological Gardens recently broke into the cage of the wart-hog.

They fought all night-long, and were found in the morning much

exhausted, but not seriously wounded. It is a significant fact, as

shewing the purpose of the above-described projections and excrescences,

that these were covered with blood, and were scored and abraded in an

extraordinary manner.

The mane of the lion forms a good defence against the one danger to

which he is liable, namely the attacks of rival lions: for the males, as

Sir. A. Smith informs me, engage in terrible battles, and a young lion

dares not approach an old one. In 1857 a tiger at Bromwich broke into

the cage of a lion, and a fearful scene ensued; "the lion's mane saved

his neck and head from being much injured, but the tiger at last

succeeded in ripping up his belly, and in a few minutes he was

dead."[324] The broad ruff round the throat and chin of the Canadian

lynx (_Felis Canadensis_) is much longer in the male than in the female;

but whether it serves as a defence I do not know. Male seals are well

known to fight desperately together, and the males of certain kinds

(_Otaria jubata_)[325] have great manes, whilst the females have small

ones or none. The male baboon of the Cape of Good Hope (_Cynocephalus

porcarius_) has a much longer mane and larger canine teeth than the

female; and the mane probably serves as a protection, for on asking the

keepers in the Zoological Gardens, without giving them any clue to my

object, whether any of the monkeys especially attacked each other by the

nape of the neck, I was answered that this was not the case, excepting

with the above baboon. In the Hamadryas baboon, Ehrenberg compares the

mane of the adult male to that of a young lion, whilst in the young of

both sexes and in the female the mane is almost absent.

It appeared to me probable that the immense woolly mane of the male

American bison, which reaches almost to the ground, and is much more

developed in the males than in the females, served as a protection to

them in their terrible battles; but an experienced hunter told Judge

Caton that he had never observed anything which favoured this belief.

The stallion has a thicker and fuller mane than the mare; and I have

made particular inquiries of two great trainers and breeders who have

had charge of many entire horses, and am assured that they "invariably

endeavour to seize one another by the neck." It does not, however,

follow from the foregoing statements, that when the hair on the neck

serves as a defence, that it was originally developed for this purpose,

though this is probable in some cases, as in that of the lion. I am

informed by Mr. McNeill that the long hairs on the throat of the stag

(_Cervus elephas_) serve as a great protection to him when hunted, for

the dogs generally endeavour to seize him by the throat; but it is not

probable that these hairs were specially developed for this purpose;

otherwise the young and the females would, as we may feel assured, have

been equally protected.

_On Preference or Choice in Pairing, as shewn by either sex of

Quadrupeds._--Before describing, in the next chapter, the differences

between the sexes in voice, odour emitted, and ornamentation, it will be

convenient here to consider whether the sexes exert any choice in their

unions. Does the female prefer any particular male, either before or

after the males may have fought together for supremacy; or does the

male, when not a polygamist, select any particular female? The general

impression amongst breeders seems to be that the male accepts any

female; and this, owing to his eagerness, is, in most cases, probably

the truth. Whether the female as a general rule indifferently accepts

any male is much more doubtful. In the fourteenth chapter, on Birds, a

considerable body of direct and indirect evidence was advanced, shewing

that the female selects her partner; and it would be a strange anomaly

if female quadrupeds, which stand higher in the scale of organisation

and have higher mental powers, did not generally, or at least often,

exert some choice. The female could in most cases escape, if wooed by a

male that did not please or excite her; and when pursued, as so

incessantly occurs, by several males, she would often have the

opportunity, whilst they were fighting together, of escaping with, or at

least of temporarily pairing with, some one male. This latter

contingency has often been observed in Scotland with female red-deer, as

I have been informed by Sir Philip Egerton.[326]

It is scarcely possible that much should be known about female

quadrupeds exerting in a state of nature any choice in their marriage

unions. The following very curious details on the courtship of one of

the eared seals, _Callorhinus ursinus_, are given[327] on the authority

of Capt. Bryant, who had ample opportunities for observation. He says,

"Many of the females on their arrival at the island where they breed

appear desirous of returning to some particular male, and frequently

climb the outlying rocks to overlook the rookeries, calling out and

listening as if for a familiar voice. Then changing to another place

they do the same again.... As soon as a female reaches the shore, the

nearest male goes down to meet her, making meanwhile a noise like the

clucking of a hen to her chickens. He bows to her and coaxes her until

he gets between her and the water so that she cannot escape him. Then

his manner changes, and with a harsh growl he drives her to a place in

his harem. This continues until the lower row of harems is nearly full.

Then the males higher up select the time when their more fortunate

neighbours are off their guard to steal their wives. This they do by

taking them in their mouths and lifting them over the heads of the other

females, and carefully placing them in their own harem, carrying them as

cats do their kittens. Those still higher up pursue the same method

until the whole space is occupied. Frequently a struggle ensues between

two males for the possession of the same female, and both seizing her at

once pull her in two or terribly lacerate her with their teeth. When the

space is all filled, the old male walks around complacently reviewing

his family, scolding those who crowd or disturb the others, and fiercely

driving off all intruders. This surveillance always keeps him actively

occupied."

As so little is known about the courtship of animals in a state of

nature, I have endeavoured to discover how far our domesticated

quadrupeds evince any choice in their unions. Dogs offer the best

opportunity for observation, as they are carefully attended to and well

understood. Many breeders have expressed a strong opinion on this head.

Thus Mr. Mayhew remarks, "The females are able to bestow their

affections; and tender recollections are as potent over them as they are

known to be in other cases, where higher animals are concerned. Bitches

are not always prudent in their loves, but are apt to fling themselves

away on curs of low degree. If reared with a companion of vulgar

appearance, there often springs up between the pair a devotion which no

time can afterwards subdue. The passion, for such it really is, becomes

of a more than romantic endurance." Mr. Mayhew, who attended chiefly to

the smaller breeds, is convinced that the females are strongly attracted

by males of large size.[328] The well-known veterinary Blaine

states[329] that his own female pug became so attached to a spaniel, and

a female setter to a cur, that in neither case would they pair with a

dog of their own breed until several weeks had elapsed. Two similar and

trustworthy accounts have been given me in regard to a female retriever

and a spaniel, both of which became enamoured with terrier-dogs.

Mr. Cupples informs me that he can personally vouch for the accuracy of

the following more remarkable case, in which a valuable and

wonderfully-intelligent female terrier loved a retriever, belonging to a

neighbour, to such a degree that she had often to be dragged away from

him. After their permanent separation, although repeatedly shewing milk

in her teats, she would never acknowledge the courtship of any other

dog, and to the regret of her owner, never bore puppies. Mr. Cupples

also states that a female deerhound now (1868) in his kennel has thrice

produced puppies, and on each occasion shewed a marked preference for

one of the largest and handsomest, but not the most eager, of four

deerhounds living with her, all in the prime of life. Mr. Cupples has

observed that the female generally favours a dog whom she has associated

with and knows; her shyness and timidity at first incline her against a

strange dog. The male, on the contrary, seems rather inclined towards

strange females. It appears to be rare when the male refuses any

particular female, but Mr. Wright, of Yeldersley House, a great breeder

of dogs, informs me that he has known some instances; he cites the case

of one of his own deerhounds, who would not take any notice of a

particular female mastiff, so that another deerhound had to be

employed. It would be superfluous to give other cases, and I will only

add that Mr. Barr, who has carefully bred many blood-hounds, states that

in almost every instance particular individuals of the opposite sex shew

a decided preference for each other. Finally Mr. Cupples, after

attending to this subject for another year, has recently written to me,

"I have had full confirmation of my former statement, that dogs in

breeding form decided preferences for each other, being often influenced

by size, bright colour, and individual character, as well as by the

degree of their previous familiarity."

In regard to horses, Mr. Blenkiron, the greatest breeder of race-horses

in the world, informs me that stallions are so frequently capricious in

their choice, rejecting one mare and without any apparent cause taking

to another, that various artifices have to be habitually used. The

famous Monarque, for instance, would never consciously look at the dam

of Gladiateur, and a trick had to be practised. We can partly see the

reason why valuable race-horse stallions, which are in such demand,

should be so particular in their choice. Mr. Blenkiron has never known a

mare to reject a horse; but this has occurred in Mr. Wright's stable, so

that the mare had to be cheated. Prosper Lucas[330] quotes various

statements from French authorities, and remarks, "On voit des etalons

qui s'eprennent d'une jument, et negligent toutes les autres." He gives,

on the authority of Baelen, similar facts in regard to bulls. Hoffberg,

in describing the domesticated reindeer of Lapland, says, "Foemina

majores et fortiores mares prae caeteris admittunt, ad eos confugiunt, a

junioribus agitatae, qui hos in fugam conjiciunt."[331] A clergyman, who

has bred many pigs, assures me that sows often reject one boar and

immediately accept another.

From these facts there can be no doubt that with most of our

domesticated quadrupeds strong individual antipathies and preferences

are frequently exhibited, and much more commonly by the female than by

the male. This being the case, it is improbable that the unions of

quadrupeds in a state of nature should be left to mere chance. It is

much more probable that the females are allured or excited by particular

males, who possess certain characters in a higher degree than other

males; but what these characters are, we can seldom or never discover

with certainty.

CHAPTER XVIII.

SECONDARY SEXUAL CHARACTERS OF MAMMALS--_continued_.

Voice--Remarkable sexual peculiarities in

seals--Odour--Development of the hair--Colour of the hair and

skin--Anomalous case of the female being more ornamented than

the male--Colour and ornaments due to sexual selection--Colour

acquired for the sake of protection--Colour, though common to

both sexes, often due to sexual selection--On the

disappearance of spots and stripes in adult quadrupeds--On the

colours and ornaments of the Quadrumana--Summary.

Quadrupeds use their voices for various purposes, as a signal of danger,

as a call from one member of a troop to another, or from the mother to

her lost offspring, or from the latter for protection to their mother;

but such uses need not here be considered. We are concerned only with

the difference between the voices of the two 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,[332] are said to be

completely mute excepting at this season. As the throats (i.e. the

larynx and thyroid bodies[333]) of stags become periodically enlarged at

the commencement of the breeding-season, it might be thought that their

powerful voices must be then in some way 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 their 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 hands in rage or agony. No doubt

stags challenge each other to mortal combat by bellowing; but it is not

likely that this habit could have led through sexual selection, that is

by the loudest-voiced males having been the most successful in their

conflicts, to the periodical enlargement of the vocal organs; for the

stags with the most powerful voices, unless at the same time the

strongest, best-armed, and most courageous, would not have gained any

advantage over their rivals with weaker voices. The stags, moreover,

which had weaker voices, though not so well able to challenge other

stags, would have been drawn to the place of combat as certainly as

those with stronger voices.

It is possible that the roaring of the lion may be of some actual

service to him in 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 any 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,[334] 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 of the year; 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, with our present state of knowledge, the most probable view.

The male gorilla has a tremendous voice, and when adult is furnished

with a laryngeal sack, as is likewise the adult male orang.[335] The

gibbons rank amongst the noisiest of monkeys, and the Sumatra species

(_Hylobates syndactylus_) is also furnished with a laryngeal sack; but

Mr. Blyth, who has had opportunities for observation, does not believe

that the male is more noisy 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 with the beaver.[336] Another

gibbon, the _H. agilis_, is highly remarkable, from having the power of

emitting a complete and correct octave of musical notes,[337] 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, when the weather is

warm, make the forests resound during the morning and evening with their

overwhelming voices. The males begin the dreadful concert, in which the

females, with their less powerful voices, sometimes join, and which is

often continued during many hours. An excellent observer, Rengger,[338]

could not perceive that they were excited to begin their concert 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 to 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 gained--I will not

pretend to say; but the former view, at least in the case of the

_Hylobates agilis_, seems the most probable.

I may here mention two very curious sexual peculiarities occurring in

seals, because they have been supposed by some writers to affect the

voice. The nose of the male sea-elephant (_Macrorhinus proboscideus_),

when about three years old, is greatly elongated during the

breeding-season, and can then be erected. In this state it is sometimes

a foot in length. The female at no period of life is thus provided, and

her voice is different. That of the male consists of a wild, hoarse,

gurgling noise, which is audible at a great distance, and is believed to

be strengthened by the proboscis. Lesson compares the erection of the

proboscis, to the swelling of the wattles of male gallinaceous birds,

whilst they court the females. In another allied kind of seal, namely,

the bladder-nose (_Cystophora cristata_), the head is covered by a great

hood or bladder. This is internally supported by the septum of the nose,

which is produced far backwards and rises into a crest seven inches in

height. The hood is clothed with short hair, and is muscular; it 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 by

man they likewise roar or bellow; and whenever irritated the bladder is

inflated. 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. This latter view is not probable, if what the

sealers have long maintained is correct, namely, that the hood or

bladder is very poorly developed in the females and in the males whilst

young.[339]

_Odour._--With some animals, as with the notorious skunk of America, the

overwhelming odour which they emit appears to serve exclusively as a

means of defence. With shrew-mice (Sorex) both sexes possess abdominal

scent-glands, and there can be little doubt, from the manner in which

their bodies are rejected by birds and beasts of prey, that their odour

is protective; nevertheless the glands become enlarged in the males

during the breeding-season. In many quadrupeds the glands are of the

same size in both sexes;[340] but their use is not known. In other

species the glands are confined to the males, or are more developed in

them 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 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 have perceived the whole air tainted with the odour of the male

_Cervus campestris_, at the distance of half a mile to leeward of a

herd; and a silk handkerchief, in which I carried home a skin, though

repeatedly 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.[341] Besides the general odour, with which the whole

body of certain ruminants seems to be permeated during 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 seen in the case of an

antelope. They are "usually larger in the male than in the female, and

their development is checked by castration."[342] According to Desmarest

they are altogether absent in the female of _Antilope subgutturosa_.

Hence, there can be no doubt that they stand in some 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, from its position, is 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.[343]

In most cases, when during the breeding-season the male alone emits a

strong odour, this 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 which are far from agreeable to us; and that dogs, though

they will not eat carrion, sniff and roll in 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 more 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 in 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 a

thin and narrow crest runs along the whole length of the back; for a

crest of this kind would afford scarcely any protection, and the ridge

of the back is not a likely place 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_[344] (see fig. 68, p. 300) and _Portax picta_, may be given as

instances. The crests of certain stags and of the male wild goat stand

erect, when these animals are enraged or terrified;[345] but it can

hardly be supposed that they have been acquired 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

front-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.

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.

The bull alone has curled hair on the forehead.[346] In three

closely-allied sub-genera of the goat family, the males alone possess

beards, sometimes of large size; in two other sub-genera both sexes have

a beard, but this disappears in some of the domestic breeds of the

common goat; and neither sex of the Hemitragus has a beard. In the ibex

the beard is not developed during the summer, and is so small at other

seasons that it may be called rudimentary.[347] With some monkeys the

beard is confined to the male, as in the Orang, or is much larger in the

male than in the female, as in the _Mycetes caraya_ and _Pithecia

satanas_ (fig. 66). So it is with the whiskers of some species of

Macacus,[348] 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.

[Illustration: Fig. 66. Pithecia Satanas, male (from Brehm).]

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

dewlap of the bull, or the crests of hair along the backs of certain

male antelopes, are of any direct or ordinary use to them. 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 which the whiskers,

moustache, and other tufts of hair on the face serve; and no one will

suppose that these are useful as a protection. Must we attribute to mere

purposeless variability in the male all these appendages of hair or

skin? It cannot be denied that this is possible; for with many

domesticated quadrupeds, certain characters, apparently not derived

through reversion from any wild parent-form, have appeared in, and are

confined to, the males, or are more largely developed in them than in

the females,--for instance the hump in the male zebu-cattle of India,

the tail in fat-tailed rams, the arched outline of the forehead in the

males of several breeds of sheep, the mane in the ram of an African

breed, and, lastly, the mane, long hairs on the hinder legs, and the

dewlap in the male alone of the Berbura goat.[349] The mane which occurs

in the rams alone of the above-mentioned African breed of sheep, is a

true secondary sexual character, for it is not developed, as I hear from

Mr. Winwood Reade, 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 African ram with a mane was descended from the same

primitive stock with the other breeds of sheep, or the Berbura male-goat

with his mane, dewlap, &c., from the same stock with other goats; and if

selection has not been applied to these characters, then they must be

due to simple variability, together with sexually-limited inheritance.

In this case it would appear reasonable to extend the same view to the

many analogous characters occurring in animals under a state of nature.

Nevertheless I cannot persuade myself that this view is applicable in

many cases, as in that of the extraordinary development of hair on the

throat and forelegs of the male Ammotragus, or of the immense beard of

the male Pithecia. With those antelopes in which the male when adult is

more strongly-coloured than the female, and with those monkeys in which

this is likewise the case, and in which the hair on the face is of a

different colour from that on the rest of the head, being arranged in

the most diversified and elegant manner, it seems probable that the

crests and tufts of hair have been acquired as ornaments; and this I

know is the opinion of some naturalists. If this view be correct, there

can be little doubt that they have been acquired, or at least modified,

through sexual selection.

_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."[350] In the _Didelphis

opossum_ of Cayenne the female is said to be a little more red than the

male. With 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."[351] 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 some few bats the fur of the male is lighter and brighter than

in the female.[352]

The terrestrial Carnivora and Insectivora rarely exhibit sexual

differences of any kind, and their colours are almost always exactly the

same in both sexes. The ocelot (_Felis pardalis_), however, offers an

exception, 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."[353] The sexes of the allied _Felis mitis_ also differ, but

even 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 very 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."[354]

With Ruminants sexual differences of colour occur more commonly than in

any other order. A difference of this kind is general with 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. The male, as I am informed by Mr. Blyth, without

shedding his hair, periodically becomes darker during the

breeding-season. Young males cannot be distinguished from young females

until above 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 distinctive of sexual colouring,

becomes obvious, when we hear[355] 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.[356]

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 have in this species, as Mr. Blyth

informs me, an exactly parallel series of facts, as with 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 undistinguishable from each other. In the

_Antilope niger_ the male is black, the female as well as the young

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 as in the female brown; 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."[357] Other analogous cases

could be added.

The Banteng bull (_Bos sondaicus_) of the Malayan archipelago is almost

black, with white legs and buttocks; the cow is of a bright dun, as are

the young males until about the age of three years, when they rapidly

change colour. The emasculated bull reverts to the colour of the female.

The female Kemas goat is paler, and the female _Capra aegagrus_ is said

to be more uniformly tinted than their respective males. Deer rarely

present any sexual differences in colour. Judge Caton, however, informs

me that with the males of the Wapiti deer (_Cervus Canadensis_) the

neck, belly, and legs are much darker than the same parts 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 nuptial plumage.[358] 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 characterise the adult

males.[359] Lastly, the mature male of the beautifully coloured and

spotted Axis deer is considerably darker, as I am informed by Mr. Blyth,

than the female; and this hue the castrated male never acquires.

The last Order which we have to consider--for I am not aware that sexual

differences in colour occur in the other mammalian groups--is that of

the Primates. The male of the _Lemur macaco_ is coal-black, whilst the

female is reddish-yellow, but highly variable in colour.[360] Of the

Quadrumana of the New World, the females and young of _Mycetes caraya_

are greyish-yellow and alike; in the second year the young male becomes

reddish-brown, in the third year 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 in _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.[361] 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 equally beautiful and curious moustache monkey (_Cercopithecus

cephus_) the only difference between the sexes is that the tail of the

male is chesnut and that of the female grey; but Mr. Bartlett informs me

that all the hues become more strongly 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 Mueller, 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.

[Illustration: Fig. 67. Head of male Mandrill (from Gervais, 'Hist. Nat

des Mammiferes').]