The Project Gutenberg ebook of Darwinism (1889), by Alfred Russel Wallace

imputes the origin of all secondary sexual characters other than weapons

of offence and defence, of all the ornamental crests and accessory

plumes of birds, the stridulating sounds of insects, the crests and

beards of monkeys and other mammals, and the brilliant colours and

patterns of male birds and butterflies. He even goes further, and

imputes to it a large portion of the brilliant colour that occurs in

both sexes, on the principle that variations occurring in one sex are

sometimes transmitted to the same sex only, sometimes to both, owing to

peculiarities in the laws of inheritance. In this extension of sexual

selection to include the action of female choice or preference, and in

the attempt to give to that choice such wide-reaching effects, I am

unable to follow him more than a very little way; and I will now state

some of the reasons why I think his views are unsound.

_Sexual Characters due to Natural Selection._

fighting with other males, there are some other sexual characters which

may have been produced by natural selection. Such are the various sounds

and odours which are peculiar to the male, and which serve as a call to

the female or as an indication of his presence. These are evidently a

valuable addition to the means of recognition of the two sexes, and are

a further indication that the pairing season has arrived; and the

production, intensification, and differentiation of these sounds and

odours are clearly within the power of natural selection. The same

remark will apply to the peculiar calls of birds, and even to the

singing of the males. These may well have originated merely as a means

of recognition between the two sexes of a species, and as an invitation

from the male to the female bird. When the individuals of a species are

widely scattered, such a call must be of great importance in enabling

pairing to take place as early as possible, and thus the clearness,

loudness, and individuality of the song becomes a useful character, and

therefore the subject of natural selection. Such is especially the case

with the cuckoo, and with all solitary birds, and it may have been

equally important at some period of the development of all birds. The

act of singing is evidently a pleasurable one; and it probably serves as

an outlet for superabundant nervous energy and excitement, just as

dancing, singing, and field sports do with us. It is suggestive of this

view that the exercise of the vocal power seems to be complementary to

the development of accessory plumes and ornaments, all our finest

singing birds being plainly coloured, and with no crests, neck or tail

plumes to display; while the gorgeously ornamented birds of the tropics

have no song, and those which expend much energy in display of plumage,

as the turkey, peacocks, birds of paradise, and humming-birds, have

comparatively an insignificant development of voice. Some birds have, in

the wings or tail, peculiarly developed feathers which produce special

sounds. In some of the little manakins of Brazil, two or three of the

wing-feathers are curiously shaped and stiffened in the male, so that

the bird is able to produce with them a peculiar snapping or cracking

sound; and the tail-feathers of several species of snipe are so narrowed

as to produce distinct drumming, whistling, or switching sounds when the

birds descend rapidly from a great height. All these are probably

recognition and call notes, useful to each species in relation to the

most important function of their lives, and thus capable of being

developed by the agency of natural selection.

_Decorative Plumage of Birds and its Display._

colours of birds, their decorative plumage, and its display at the

pairing season; and it is on this latter circumstance that he founds his

theory, that both the plumage and the colours have been developed by the

preference of the females, the more ornamented males becoming the

parents of each successive generation. Any one who reads these most

interesting chapters will admit, that the fact of the display is

demonstrated; and it may also be admitted, as highly probable, that the

female is pleased or excited by the display. But it by no means follows

that slight differences in the shape, pattern, or colours of the

ornamental plumes are what lead a female to give the preference to one

male over another; still less that all the females of a species, or the

great majority of them, over a wide area of country, and for many

successive generations, prefer exactly the same modification of the

colour or ornament.
The evidence on this matter is very scanty, and in most cases not at all

to the point. Some peahens preferred an old pied peacock; albino birds

in a state of nature have never been seen paired with other birds; a

Canada goose paired with a Bernicle gander; a male widgeon preferred a

pintail duck to its own species; a hen canary preferred a male

greenfinch to either linnet, goldfinch, siskin, or chaffinch. These

cases are evidently exceptional, and are not such as generally occur in

nature; and they only prove that the female does exert some choice

between very different males, and some observations on birds in a state

of nature prove the same thing; but there is no evidence that slight

variations in the colour or plumes, in the way of increased intensity or

complexity, are what determines the choice. On the other hand, Mr.

Darwin gives much evidence that it is _not_ so determined. He tells us

that Messrs. Hewitt, Tegetmeier, and Brent, three of the highest

authorities and best observers, "do not believe that the females prefer

certain males on account of the beauty of their plumage." Mr. Hewitt was

convinced "that the female almost invariably prefers the most vigorous,

defiant, and mettlesome male;" and Mr. Tegetmeier, "that a gamecock,

though disfigured by being dubbed, and with his hackles trimmed, would

be accepted as readily as a male retaining all his natural

ornaments."[126] Evidence is adduced that a female pigeon will sometimes

turn antipathy to a particular male without any assignable cause; or, in

other cases, will take a strong fancy to some one bird, and will desert

her own mate for him; but it is not stated that superiority or

inferiority of plumage has anything to do with these fancies. Two

instances are indeed given, of male birds being rejected, which had lost

their ornamental plumage; but in both cases (a widow-finch and a silver

pheasant) the long tail-plumes are the indication of sexual maturity.

Such cases do not support the idea that males with the tail-feathers a

trifle longer, or the colours a trifle brighter, are generally

preferred, and that those which are only a little inferior are as

generally rejected,--and this is what is absolutely needed to establish

the theory of the development of these plumes by means of the choice of

the female.

in the matter of their partners, just as we have ourselves, and this may

afford us an illustration. A young man, when courting, brushes or curls

his hair, and has his moustache, beard, or whiskers in perfect order,

and no doubt his sweetheart admires them; but this does not prove that

she marries him on account of these ornaments, still less that hair,

beard, whiskers, and moustache were developed by the continued

preferences of the female sex. So, a girl likes to see her lover well

and fashionably dressed, and he always dresses as well as he can when he

visits her; but we cannot conclude from this that the whole series of

male costumes, from the brilliantly coloured, puffed, and slashed

doublet and hose of the Elizabethan period, through the gorgeous coats,

long waistcoats, and pigtails of the early Georgian era, down to the

funereal dress-suit of the present day, are the direct result of female

preference. In like manner, female birds may be charmed or excited by

the fine display of plumage by the males; but there is no proof whatever

that slight differences in that display have any effect in determining

their choice of a partner.

_Display of Decorative Plumage._
The extraordinary manner in which most birds display their plumage at

the time of courtship, apparently with the full knowledge that it is

beautiful, constitutes one of Mr. Darwin's strongest arguments. It is,

no doubt, a very curious and interesting phenomenon, and indicates a

connection between the exertion of particular muscles and the

development of colour and ornament; but, for the reasons just given, it

does not prove that the ornament has been developed by female choice.

During excitement, and when the organism develops superabundant energy,

many animals find it pleasurable to exercise their various muscles,

often in fantastic ways, as seen in the gambols of kittens, lambs, and

other young animals. But at the time of pairing, male birds are in a

state of the most perfect development, and possess an enormous store of

vitality; and under the excitement of the sexual passion they perform

strange antics or rapid flights, as much probably from an internal

impulse to motion and exertion as with any desire to please their mates.

Such are the rapid descent of the snipe, the soaring and singing of the

lark, and the dances of the cock-of-the-rock and of many other birds.
It is very suggestive that similar strange movements are performed by

many birds which have no ornamental plumage to display. Goatsuckers,

geese, carrion vultures, and many other birds of plain plumage have been

observed to dance, spread their wings or tails, and perform strange

love-antics. The courtship of the great albatross, a most unwieldy and

dull coloured bird, has been thus described by Professor Moseley: "The

male, standing by the female on the nest, raises his wings, spreads his

tail and elevates it, throws up his head with the bill in the air, or

stretches it straight out, or forwards, as far as he can, and then

utters a curious cry."[127] Mr. Jenner Weir informs me that "the male

blackbird is full of action, spreads out his glossy wing and tail, turns

his rich golden beak towards the female, and chuckles with delight,"

while he has never seen the more plain coloured thrush demonstrative to

the female. The linnet distends his rosy breast, and slightly expands

his brown wings and tail; while the various gay coloured Australian

finches adopt such attitudes and postures as, in every case, to show off

their variously coloured plumage to the best advantage.[128]

_A Theory of Animal Coloration._

account for the brilliant colours and markings of the higher animals,

the preponderance of these colours and markings in the male sex, and

their display during periods of activity or excitement, I may be asked

what explanation I have to offer as a preferable substitute. In my

_Tropical Nature_ I have already indicated such a theory, which I will

now briefly explain, supporting it by some additional facts and

arguments, which appear to me to have great weight, and for which I am

mainly indebted to a most interesting and suggestive posthumous work by

Mr. Alfred Tylor.[129]

preceding chapters, very largely protective, and it is not improbable

that the primitive colours of all animals were so. During the long

course of animal development other modes of protection than concealment

by harmony of colour arose, and thenceforth the normal development of

colour due to the complex chemical and structural changes ever going on

in the organism, had full play; and the colours thus produced were again

and again modified by natural selection for purposes of warning,

recognition, mimicry, or special protection, as has been already fully

explained in the preceding chapters.

which underlies the various patterns or ornamental markings of

animals--namely, that diversified coloration follows the chief lines of

structure, and changes at points, such as the joints, where function

changes. He says, "If we take highly decorated species--that is, animals

marked by alternate dark or light bands or spots, such as the zebra,

some deer, or the carnivora, we find, first, that the region of the

spinal column is marked by a dark stripe; secondly, that the regions of

the appendages, or limbs, are differently marked; thirdly, that the

flanks are striped or spotted, along or between the regions of the lines

of the ribs; fourthly, that the shoulder and hip regions are marked by

curved lines; fifthly, that the pattern changes, and the direction of

the lines, or spots, at the head, neck, and every joint of the limbs;

and lastly, that the tips of the ears, nose, tail, and feet, and the eye

are emphasised in colour. In spotted animals the greatest length of the

spot is generally in the direction of the largest development of the

skeleton."
This structural decoration is well seen in many insects. In

caterpillars, similar spots and markings are repeated in each segment,

except where modified for some form of protection. In butterflies, the

spots and bands usually have reference to the form of the wing and the

arrangement of the nervures; and there is much evidence to show that the

primitive markings are always spots in the cells, or between the

nervures, or at the junctions of nervures, the extension and coalescence

of these spots forming borders, bands, or blotches, which have become

modified in infinitely varied ways for protection, warning, or

recognition. Even in birds, the distribution of colours and markings

follows generally the same law. The crown of the head, the throat, the

ear-coverts, and the eyes have usually distinct tints in all highly

coloured birds; the region of the furcula has often a distinct patch of

colour, as have the pectoral muscles, the uropygium or root of the tail,

and the under tail-coverts.[130]
Mr. Tylor was of opinion the primitive form of ornamentation consisted

of spots, the confluence of these in certain directions forming lines or

bands; and, these again, sometimes coalescing into blotches, or into

more or less uniform tints covering a large portion of the surface of

the body. The young lion and tiger are both spotted; and in the Java hog

(Sus vittatus) very young animals are banded, but have spots over the

shoulders and thighs. These spots run into stripes as the animal grows

older; then the stripes expand, and at last, meeting together, the adult

animal becomes of a uniform dark brown colour. So many of the species of

deer are spotted when young, that Darwin concludes the ancestral form,

from which all deer are derived, must have been spotted. Pigs and tapirs

are banded or spotted when young; an imported young specimen of Tapirus

Bairdi was covered with white spots in longitudinal rows, here and there

forming short stripes.[131] Even the horse, which Darwin supposes to be

descended from a striped animal, is often spotted, as in dappled horses;

and great numbers show a tendency to spottiness, especially on the

haunches.
Ocelli may also be developed from spots, or from bars, as pointed out by

Mr. Darwin. Spots are an ordinary form of marking in disease, and these

spots sometimes run together, forming blotches. There is evidence that

colour markings are in some way dependent on nerve distribution. In the

disease known as frontal herpes, an eruption occurs which corresponds

exactly to the distribution of the ophthalmic division of the fifth

cranial nerve, mapping out all its little branches even to the one which

goes to the tip of the nose. In a Hindoo suffering from herpes the

pigment was destroyed in the arm along the course of the ulnar nerve,

with its branches along both sides of one finger and the half of

another. In the leg the sciatic and scaphenous nerves were partly mapped

out, giving to the patient the appearance of an anatomical diagram.[132]

general dependence of marking on structure which has been already

pointed out. For, as the nerves everywhere follow the muscles, and these

are attached to the various bones, we see how it happens, that the

tracts in which distinct developments of colour appear, should so often

be marked out by the chief divisions of the bony structure in

vertebrates, and by the segments in the annulosa. There is, however,

another correspondence of even greater interest and importance.

Brilliant colours usually appear just in proportion to the development

of tegumentary appendages. Among birds the most brilliant colours are

possessed by those which have developed frills, crests, and elongated

tails like the humming-birds; immense tail-coverts like the peacock;

enormously expanded wing-feathers, as in the argus-pheasant; or

magnificent plumes from the region of the coracoids in many of the birds

of paradise. It is to be noted, also, that all these accessory plumes

spring from parts of the body which, in other species, are distinguished

by patches of colour; so that we may probably impute the development of

colour and of accessory plumage to the same fundamental cause.

butterflies and moths, groups in which the wing-membranes have received

their greatest expansion, and whose specialisation has been carried

furthest in the marvellous scaly covering which is the seat of the

colour. It is suggestive, that the only other group in which functional

wings are much coloured is that of the dragonflies, where the membrane

is exceedingly expanded. In like manner, the colours of beetles, though

greatly inferior to those of the lepidoptera, occur in a group in which

the anterior pair of wings has been thickened and modified in order to

protect the vital parts, and in which these wing-covers (elytra), in the

course of development in the different groups, must have undergone great

changes, and have been the seat of very active growth.

_The Origin of Accessory Plumes._
Mr. Darwin supposes, that these have in almost every case been developed

by the preference of female birds for such males as possessed them in a

higher degree than others; but this theory does not account for the fact

that these plumes usually appear in a few definite parts of the body. We

require some cause to initiate the development in one part rather than

in another. Now, the view that colour has arisen over surfaces where

muscular and nervous development is considerable, and the fact that it

appears especially upon the accessory or highly developed plumes, leads

us to inquire whether the same cause has not primarily determined the

development of these plumes. The immense tuft of golden plumage in the

best known birds of paradise (Paradisea apoda and P. minor) springs

from a very small area on the side of the breast. Mr. Frank E. Beddard,

who has kindly examined a specimen for me, says that "this area lies

upon the pectoral muscles, and near to the point where the fibres of the

muscle converge towards their attachment to the humerus. The plumes

arise, therefore, close to the most powerful muscle of the body, and

near to where the activities of that muscle would be at a maximum.

Furthermore, the area of attachment of the plumes is just above the

point where the arteries and nerves for the supply of the pectoral

muscles, and neighbouring regions, leave the interior of the body. The

area of attachment of the plume is, also, as you say in your letter,

just above the junction of the coracoid and sternum." Ornamental plumes

of considerable size rise from the same part in many other species of

paradise birds, sometimes extending laterally in front, so as to form

breast shields. They also occur in many humming-birds, and in some

sun-birds and honey-suckers; and in all these cases there is a wonderful

amount of activity and rapid movement, indicating a surplus of vitality,

which is able to manifest itself in the development of these accessory

plumes.[133]
In a quite distinct set of birds, the gallinaceae, we find the

ornamental plumage usually arising from very different parts, in the

form of elongated tail-feathers or tail-coverts, and of ruffs or hackles

from the neck. Here the wings are comparatively little used, the most

constant activities depending on the legs, since the gallinaceae are

pre-eminently walking, running, and scratching birds. Now the

magnificent train of the peacock--the grandest development of accessory

plumes in this order--springs from an oval or circular area, about three

inches in diameter, just above the base of the tail, and, therefore,

situated over the lower part of the spinal column near the insertion of

the powerful muscles which move the hind limbs and elevate the tail. The

very frequent presence of neck-ruffs or breast-shields in the males of

birds with accessory plumes may be partly due to selection, because they

must serve as a protection in their mutual combats, just as does the

lion's or the horse's mane. The enormously lengthened plumes of the bird

of paradise and of the peacock can, however, have no such use, but must

be rather injurious than beneficial in the bird's ordinary life. The

fact that they have been developed to so great an extent in a few

species is an indication of such perfect adaptation to the conditions of

existence, such complete success in the battle for life, that there is,

in the adult male at all events, a surplus of strength, vitality, and

growth-power which is able to expend itself in this way without injury.

That such is the case is shown by the great abundance of most of the

species which possess these wonderful superfluities of plumage. Birds of

paradise are among the commonest birds in New Guinea, and their loud

voices can be often heard when the birds themselves are invisible in the

depths of the forest; while Indian sportsmen have described the peafowl