Page images


mammalia. Whenever there is a dif- the organism, increasing vigour acting ference of colour between the sexes the unequally on different portions of the male is the darker or more strongly integument, and often producing at the marked, and difference of intensity is same time abnormal developments of most visibled uring the breeding season; hair, horns, scales, feathers, &c., would (Descent of Man, p. 533). Numerous almost necessarily lead also to variable cases among domestic animals also distribution of colour, and thus to the prove, that there is an inherent ten- production of new tints and markdency in the male to special develop- ings. These acquired colours would, ments of dermal appendages and as Mr. Darwin has shown, be transcolour, quite independently of sexual mitted to both sexes or to one only, or any other form of selection. Thus, according as they first appeared at “the hump on the male zebu cattle of an early age, or in adults of India, the tail of fat-tailed rams, the sex, and thus we may account for arched outline of the forehead in the some of the most marked differences males of several breeds of sheep, and in this respect. With the exception the mane, the long hairs on the hind- of butterflies, the sexes

are almost legs, and the dewlap of the male of alike in the great majority of insects. the Berbura goat,” are all adduced by The same is the case in mammals Mr. Darwin as instances of characters and reptiles, while the chief departure peculiar to the male, yet not derived from the rule occurs in birds, though from any parent ancestral form.

even here in very many cases the law Among domestic pigeons the character of sexual likeness prevails. But in all of the different breeds is often most cases where the increasing developstrongly manifested in the male birds; ment of colour became disadvantageous the wattle of the carriers and the eye- to the female, it would be checked by wattles of the barbs are largest in the natural selection, and thus produce males, and male pouters distend their those numerous instances of protective crops to a much greater extent than colouring in the female only, which do the females, and the cock fantails occur in these two groups of animals. often have a greater number of tail- There is also, I believe, a very feathers than the females. There are important purpose and use of the also some varieties of pigeons of which varied colours of the higher animals, the males are striped or spotted with in the facility it affords for recogniblack while the females are never so tion by the sexes or by the young of spotted (Animals and Plants under

the same species ; and it is this use Domestication, I. 161); yet in the which probably fixes and determines parent stock of these pigeons there the coloration in many cases.

When are no differences between the sexes differences of size and form are very either of plumage or colour, and arti- slight, colour affords the only means ficial selection has not been applied to of recognition at a distance or while in produce them.

motion, and such a distinctive character The greater intensity of coloration must therefore be of especial value to in the male—which may be termed the flying insects which are continually in normal sexual difference, would be motion, and encounter each other, as further developed by the combats of it were, by accident. This view offers the males for the possession of the us an explanation of the curious fact, females. The most vigorous and ener- that among butterflies the females of getic usually being able to rear most closely-allied species in the same offspring, intensity of colour, if de- locality sometimes differ considerably, pendent on, or correlated with vigour, while the males are much alike ; for would tend to increase. But as differ- as the males are the swiftest and the ences of colour depend upon minute highest fliers and seek the females, chemical or structural differences in it would evidently be advantageous


for them to be able to recognize hasty to declare that the stripes their true partners at some distance “cannot afford any protection." off. This peculiarity occurs with The wonderful display and endless many species of Papilio, Diadema, variety of colour in which butterflies Adolias, and Colias. In birds such and birds so far exceed all other marked differences of colour are not animals, seems primarily due to the required, owing to their higher organi- excessive development and endless sation and more perfect senses, which variations of the integumentary strucrender recognition easy by means of a tures. No insects have such widely combination of very slight differential expanded wings in proportion to their characters. This principle may, per

bodies as butterflies and moths; in haps, however, account for some ano- none do the wings vary so much in malies of coloration among the higher size and form, and in none are they animals. Thus, Mr. Darwin, while clothed with such a beautiful and admitting that the hare and the rabbit highly-organized coating of scales. are coloured protectively, remarks that According to the general principles of the latter, while running to its bur- the production of colour already exrow, is made conspicuous to the plained, these long-continued expansportsman, and doubt to all sions of membranes and developments beasts of prey, by its upturned white of surface-structures must have led to tail. But this very conspicuousness numerous colour-changes, which have while running away, may be useful as been sometimes checked, sometimes a signal and guide to the young, who fixed and utilised, sometimes intensiare thus enabled to escape danger by fied, by natural selection, according to following the older rabbits, directly the needs of the animal. In birds, and without hesitation, to the safety too, we have the wonderful clothing of the burrow; and this may be the of plumage--the most highly organmore important from the semi-noctur- ised, the most varied, and the most nal habits of the animal. If this ex- expanded of all dermal appendages. planation is correct, and it certainly The endless processes of growth and seems probable, it may serve as a change during the development of warning of how impossible it is, with- feathers, and the enormous extent of out exact knowledge of the habits of this delicately-organised surface, must an animal and a full consideration of have been highly favourable to the all the circumstances, to decide that production of varied colour-effects, any particular coloration cannot be which, when not injurious, have been protective or in any way useful. Mr. merely fixed for purposes of specific Darwin himself is not free from such identification, but have often been assumptions. Thus, he says: “The modified or suppressed whenever differzebra is conspicuously striped, and ent tints were needed for purposes of stripes cannot afford any protection protection on the open plains of South Africa.” To voluntary sexual selection, that But the zebra is a very swift animal, is, the actual choice by the females of and, when in herds, by no means the more brilliantly-coloured males, I void of means of defence. The stripes believe very little if any effect is therefore may be of use by enabling directly due. It is undoubtedly proved stragglers to distinguish their fellows that in birds the females do sometimes at a distance, and they may be even exert a choice; but the evidence of protective when the animal is at rest this fact collected by Mr. Darwin among herbage-the only time when (Descent of Man, chap. xiv.) does not it would need protective colouring. prove that colour determines that Until the habits of the zebra have choice, while much of the strongest been observed with special reference evidence is directly opposed to this to this point, it is surely somewhat view. All the facts appear to be con

sistent with the choice depending on a the less highly-coloured birds would variety of male characteristics, with be at no disadvantage as regards some of which colour is often corre- leaving healthy offspring. If, howlated. Thus it is the opinion of some ever, heightened colour is correlated of the best observers that vigour and with health and vigour, and these liveliness are most attractive, and healthy and vigorous birds provide these are no doubt usually associated best for their young, and leave offwith intensity of colour. Again, the spring which, being equally healthy display of the various ornamental ap and vigorous, can best provide for pendages of the male during courtship themselves, then natural selection may be attractive, but these appen- becomes a preserver and intensifier dages, with their bright colours or of colour. Another most important shaded patterns, are due probably to consideration is, that male butterflies general laws of growth and to that rival or even excel the most gorgeous superabundant vitality which we have male birds in bright colours and seen to be a cause of colour. But elegant patterns; and among these there are many considerations which there is literally not one particle of seem to show that the possession of evidence that the female is influenced these ornamental appendages and by colour or even that she has any bright colours in the male is not an power of choice, while there is much important character functionally, and direct evidence to the contrary that it has not been produced by the (Descent of Man, p. 318). The weakaction of voluntary sexual selection. ness of the evidence for sexual selecAmid the copious mass of facts and tion among these insects is so palopinions collected by Mr. Darwin as to pable that Mr. Darwin is obliged to the display of colour and ornaments by supplement it by the singularly inthe male birds, there is a total ab- conclusive argument that, “Unless sence of


evidence that the females the females prefer one male to anadmire or even notice this display. other, the pairing must be left to mere The hen, the turkey, and the pea- chance, and this does not appear profowl go on feeding while the male is bable (l.c., p. 317).” But he has just displaying his finery, and there is said—“The males sometimes fight reason to believe that it is his per- together in rivalry, and many may be sistency and energy rather than his

seen pursuing or crowding round the beauty which wins the day. Again, same female ;” while in the case of evidence collected by Mr. Darwin the silk-moths, “the females appear himself proves that each bird finds a not to evince the least choice in regard mate under any circumstances. He to their partners." Surely the plain gives a number of cases of one of a inference from all this is, that males pair of birds being shot, and the sur- fight and struggle for the almost vivor being always found paired again passive female, and that the most almost immediately. This is suffi- vigorous and energetic, the strongestciently explained on the assumption winged or the most persevering, wins that the destruction of birds by her. How can there be chance in various causes is continually leaving this? Natural selection would here widows and widowers in nearly equal act, as in birds, in perpetuating the proportions, and thus each one finds a strongest and most vigorous males, and fresh mate; and it leads to the con- as these would usually be the more clusion that permanently unpaired highly coloured of their race, the same birds are very scarce; so that, speak- results would be produced as regards ing broadly, every bird finds a mate the intensification and variation of and breeds. But this would almost colour in the one case as in the other. or quite neutralize any effect of sexual

Let us now

see how these prinselection of colour or ornament, since ciples will apply to some of the cases No. 215.- VOL. XXXVI.



[ocr errors]



for them to be able to recognize hasty to declare that

s, we have their true partners at some distance

- cannot afford any p?

ientation in off. This peculiarity occurs with The wonderful ?

at to account many species of Papilio, Diadema, variety of colour.

hout believing Adolias, and Colias. In birds such and birds SO

illiant males by marked differences of colour are not animals, seer

h there is not a required, owing to their higher organi- excessive d

The facts given sation and more perfect senses, which variations ;

erflies and other render recognition easy by means of a


quish colours and combination of very slight differential expand

colours similar to characters. This principle may, per


uite consistent with haps, however, account for some ano

our, which continually malies of coloration among the higher si

wr, is utilised for puranimals. Thus, Mr. Darwin, while

ntification and distinction, admitting that the hare and the rabbit

required to be modified or are coloured protectively, remarks that

ssed for purposes of protection. the latter, while running to its bu

cases of the females of some row, is made conspicuous to

pecies of Thecla, Callidryas, Colias, sportsman, and no doubt to

and Hipparchia, which have more conbeasts of prey, by its upturned

spicuous markings than the male, may tail. But this very conspicy

be due to several causes: to obtain while running away, may be

greater distinction from other species, a signal and guide to the

weated to

for protection from birds, as in the are thus enabled to escar

I am not case of the yellow-underwing moths, following the older ral aver main- while sometimes--as in Hipparchiaand without hesitatio

e colours of the lower intensity of colouring in the of the burrow; and

female may lead to more contrasted more important fro

protection, markings. Mr. Darwin thinks that nal habits of the

self referred

here the males have selected the more planation is cor

Ovilliant colour

beautiful females, although one chief seems probab)


for protection; fact in support of his theory of volunwarning of }

spots on the hind tary sexual selection is, that throughout out exact 1

which are pierced by the whole animal kingdom the males an animal

are usually so ardent that they will acwere the vital parts of all the

se she bright patch on cept any female, while the females are

butterflies which Mr. coy, and choose the handsomest males, prote:

are protective, may whence it is believed the general Dar

we purpose. It is in fact brilliancy of males as compared with assy markable how very gene

females has arisen. black spots, ocelli, or bright Perhaps the most curious cases of s'

plour are on the tips, mar- sexual difference of colour are those in We of the wings; and as the which the female is very much more

ere necessarily visible while gaily coloured than the male. This and this is the time when they

occurs most strikingly in some species were subject to attacks by insecti- of Pieris in South America, and of

Diadema in the Malay islands, and in Nous parts at some distance from

both cases the females resemble species

of the uneatable Danaidæ and Helihe body may be a real protection to

Again, Mr. Darwin admits conidæ, and thus gain a protection. at the white colour of the male In the case of Pieris pyrrha, P. malenka, Chase-moth may render it more easily and P. lorena, the males are plain sen by the female while flying about

white and black, while the females are in the dusk, and if to this we add

orange, yellow, and black, and so that it will be also more readily dis

banded and spotted as exactly to

[ocr errors]

attvaly been




cies of Heliconidæ. Mr. for particular Males by the Females,"

that these females the facts quoted show indifference to nge colours as a pro- colour, except that some colour similar re is no apparent to their own seems to be preferred. But nitation of the in the case of the hen canary, who helieves that chose a greenfinch in preference to a male by either chaffinch or goldfinch, gay

This colours had evidently no preponder'ition ating attraction.

There is some evial dence adduced that female birds may,

and probably do, choose their mates, but none whatever that the choice is

determined by difference of colour ; hus and no less than three eminent breeders

been informed Mr. Darwin that they “ did ne thinks

not believe that the females prefer tly

had certain males on account of the beauty every trace of

of their plumage.” Again, Mr. Daru must suppose it win himself says :

as a general rule ucurring during the colour appears to have little influence tions which resulted in on the pairing of pigeons.” The oftellous change in herself, quoted case of Sir R. Heron's peahens consider the fact that the which preferred an “old pied cock » frequent the forests where the to those normally coloured, is a very iconidæ abound, while the males unfortunate one, because pied birds y much in the open, and assemble in are just those that are not favoured in great numbers with other white and a state of nature, or the breeds of wild yellow butterflies on the banks of birds would become as varied and rivers, may it not be possible that mottled as our domestic varieties. If the appearance of orange stripes or such irregular fancies were not rare patches would be as injurious to the exceptions the production of definite male as it is useful to the female, by colours and patterns by the choice of making him a more easy mark for in- the female birds, or in any other way, sectivorous birds among his white would be impossible. companions ? This seems a more pro- We now come to such wonderful bable supposition, than the altogether developments of plumage and colour hypothetical choice of the female, as are exhibited by the peacock and sometimes exercised in favour of and the Argus-pheasant; and I may here sometimes against every new variety mention that it was the case of the of colour in her partner.

latter bird, as fully discussed by Mr. The full and interesting account Darwin, which first shook my belief given by Mr. Darwin of the colours in “sexual,” or

properly and habits of male and female b'rds “ female" selection. The long series (Descent of Man, chapters xiii. and of gradations, by which the beautifully xiv.), proves that in most, if not in all shaded ocelli on the secondary wingcases, the male birds fully display feathers of this bird have been protheir ornamental plumage, before the duced, are clearly traced out, the refemales and in rivalry with each sult being a set of markings, so exother; but on the essential point of quisitely shaded as to represent

“ balls whether the female's choice is deter- lying loose within sockets,"— purely mimed by minute differences in these artificial objects of which these birds ornaments or in their colours, there could have no possible knowledge. appears to be an entire absence of That this result should have been evidence. In the section on “Preference attained through thousands and tens


« EelmineJätka »