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adduced by Mr. Darwin in support tinguished from allied species, we have of his theory of voluntary sexual a reason for diverse ornamentation in selection,
these insects quite sufficient to account In Descent of Man, 2nd ed., pp. for most of the facts, without believing 307-316, we find an elaborate account in the selection of brilliant males by of the various modes of colouring of the females, for which there is not a butterflies and moths, proving that the particle of evidence. The facts given coloured parts are always more or less to show that butterflies and other displayed, and that they have some insects can distinguish colours and evident relation to an observer. Mr. are attracted by colours similar to Darwin then says—“From the several their own, are quite consistent with foregoing facts it is impossible to admit the view that colour, which continually that the brilliant colours of butterflies, tends to appear, is utilised for purand of some few moths, have com- poses of identification and distinction, monly been acquired for the sake of when not required to be modified or protection. We have seen that their suppressed for purposes of protection. colours and elegant patterns The cases of the females of some arranged and exhibited as if for dis- species of Thecla, Callidryas, Colias, play. Hence I am led to believe that and Hipparchia, which have more conthe females prefer or are most excited spicuous markings than the male, may by the more brilliant males; for on be due to several causes : to obtain any other supposition the males would, greater distinction from other species, as far as we can see, be ornamented to for protection from birds, as in the no purpose" (l.c., p. 316). I am not case of the yellow-underwing moths, aware that any one has ever main- while sometimes--as in Hipparchiatained that the brilliant colours of the lower intensity of colouring in the butterflies have “commonly been female
lead to more contrasted acquired for the sake of protection,” markings. Mr. Darwin thinks that yet Mr. Darwin has himself referred here the males have selected the more to cases in which the brilliant colour beautiful females, although one chief is so placed as to serve for protection; fact in support of his theory of volunas for example, the eye-spots on the hind tary sexual selection is, that throughout wings of moths, which are pierced by the whole animal kingdom the males birds and so save the vital parts of are usually so ardent that they will acthe insect, while the bright patch on cept any female, while the females are the orange-tip butterflies which Mr. coy, and choose the handsomest males, Darwin denies are protective, may
whence it is believed the general serve the same purpose. It is in fact brilliancy of males as compared with somewhat remarkable how very gene
females has arisen. rally the black spots, ocelli, or bright Perhaps the most curious cases of patches of colour are on the tips, mar- sexual difference of colour are those in gins, or discs of the wings; and as the which the female is very much more insects are necessarily visible while gaily coloured than the male. This flying, and this is the time when they occurs most strikingly in some species are most subject to attacks by insecti- of Pieris in South America, and of vorous birds, the position of the more Diadema in the Malay islands, and in conspicuous parts at some distance from both cases the females resemble species the body may be a real protection to of the uneatable Danaidæ and Helithem. Again, Mr. Darwin admits conidæ, and thus gain a protection. that the white colour of the male In the case of Pieris pyrrha, P. malenka, Ghost-moth
render it more easily and P. lorena, the males are plain seen 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 80 that it will be also more readily dis- banded and spotted as exactly to
resemble species of Heliconidæ. Mr. for particular Males by the Females," Darwin admits that these females the facts quoted show indifference to have acquired these colours as a pro- colour, except that some colour similar tection; but as there is no apparent to their own seems to be preferred. But cause for the strict limitation of the in the case of the hen canary, who colour to the female, he believes that chose a greenfinch in preference to it has been kept down in the male by either chaffinch or goldfinch, gay its being unattractive to her. This colours had evidently no preponderappears to me to be a supposition ating attraction. There is some eviopposed to the whole theory of sexual dence adduced that female birds may, selection itself. For this theory is, and probably do, choose their mates, that minute variations of colour in but none whatever that the choice is the male are attractive to the female, determined by difference of colour; have always been selected, and that thus and no less than three eminent breeders the brilliant male colours have been informed Mr. Darwin that they “ did produced. But in this case he thinks not believe that the females prefer that the female butterfly had certain males on account of the beauty constant aversion to every trace of of their plumage.” Again, Mr. Darcolour, even when we must suppose it
win himself says :
as a general rule was constantly recurring during the colour
to have little influence successive variations which resulted in on the pairing of pigeons." The oftsuch a marvellous change in herself. quoted case of Sir R. Heron's peahens But if we consider the fact that the which preferred an “old pied cock” females frequent the forests where the to those normally coloured, is a very Heliconidæ abound, while the males unfortunate one, because pied birds fly 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,"
properly and habits of male and female bʻrds “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
of thousands of female birds all pre- upon the “most vigorous, defiant, and ferring those males whose markings mettlesome male ; ” and if we further varied slightly in this one direction, believe, what is certainly the case, that this uniformity of choice continuing these are as a rule the most brightly through thousands and tens of thou- coloured and adorned with the finest sands of generations, is to me absolutely developments of plumage, we have a incredible. And, when further, we re- real and not a hypothetical cause at member that those which did not so work. For these most healthy, vigorvary would also, according to all the ous, and beautiful males will have the evidence, find mates and leave off- choice of the finest and most healthy spring, the actual result seems quite females, will have the most numerous impossible of attainment by such and healthy families, and will be
able best to protect and rear those Without pretending to solve com- families. Natural selection, and what pletely so difficult a problem, I would may be termed male selection, will point out a circumstance which seems tend to give them the advantage in to afford a clue. It is, that the most the struggle for existence, and thus highly-coloured and most richly- the fullest plumage and the finest varied markings, occur on those parts colours will be transmitted, and tend of the plumage which have undergone to advance in each succeeding generathe greatest modification, or have tion. acquired the most abnormal develop- There remains, however, what Mr. ment. In the peacock, the tail-coverts Darwin evidently considers his strongare enormously developed, and the est argument — the display by the "eyes” are situated on the greatly male of each species of its peculiar dilated ends. In the birds of para
beauties of plumage and colour. dise, breast, or neck, or head, or tail- We have here, no doubt, a very refeathers, are greatly developed and markable and very interesting fact highly coloured. The hackles of the but this too may be explained by cock, and the scaly breasts of hum- general principles, quite independent ming-birds are similar developments; of any choice or volition of the female while in the Argus-pheasant the bird. During pairing-time, the male secondary quills are so enormously
so enormously bird is in a state of great excitement, lengthened and broadened as to have and full of exuberant energy. Even 'become almost useless for flight. Now unornamented birds flutter their wings it is easily conceivable, that during or spread them out, erect their tails this process of development, ine- or crests, and thus give vent to the qualities in the distribution of colour nervous excitability with which they may have arisen in different parts of are overcharged. It is not improbable the same feather, and that spots and that crests and other erectile feathers bands may thus have become broad- may be primarily of use in frightening ened out into shaded spots or ocelli, away enemies, since they are generally in the way indicated by Mr. Darwin, erected when angry or during combat. much as the spots and rings on a soap
Those individuals who were most bubble increase with increasing tenuity. pugnacious and defiant, and who This is the more probable, as in brought these erectile plumes most domestic fowls varieties tend to be frequently and most powerfully into come symmetrical, quite independently action, would tend to increase them of sexual selection. (Descent of Man, by use, and to leave them further p. 424.)
developed in some of their descendants. If now we accept the evidence of If, in the course of this development, Mr. Darwin's most trustworthy cor- colour appeared, we have every reason respondents, that the choice of the to believe it would be most vivid in female, so far as she exerts any, falls these most pugnacious and energetic
individuals, and as these would always for this is, that a small fraction of the have the advantage in the rivalry for least ornamented do not obtain mates, mates (to which advantage the excess while a few of the most ornamented of colour and plumage might some- may leave more than the average numtimes conduce), there seems nothing ber of offspring.
ber of offspring. Unless, therefore, to prevent a progressive development there is the strictest correlation beof these ornaments in all dominant tween ornament and general perfecraces, that is, wherever there was such tion, the former can have no permanent a surplus of vitality, and such com- advantage; and if there is (as I mainplete adaptation to conditions, that the tain) such a correlation, then the sexual inconvenience or danger produced by selection of ornament for which there them, was so comparatively small as is little or no evidence becomes neednot to affect the superiority of the less, because natural selection which race over its nearest allies. If then is an admitted vera causa will itself those portions of the plumage, which produce all the results. In the case were originally erected and displayed, of butterflies the argument becomes became developed and coloured, the even stronger, because the fertility is actual display, under the influence of so much greater, and the weeding out jealousy or sexual excitement becomes of the unfit takes place, to a great intelligible. The males, in their extent, in the egg and larvæ state. rivalry with each other, would see Unless the eggs and larva which eswhat plumes were most effective, and caped to produce the next generation each would endeavour to excel his were those which would produce the enemy as far as voluntary exertion more highly-coloured butterflies, it is could effect it, just as they endeavour difficult to perceive how the slight to rival each other in song, even some- preponderance of colour sometimes times to the point of causing their selected by the females, should not be own destruction.
wholly neutralised by the extremely There is also a general argument rigid selection for other qualities to against Mr. Darwin's views on this which the offspring in every stage are question, founded on the nature and exposed. The only way in which we potency of “natural” as opposed to can account for the observed facts is,
sexual” selection, which appears to by the supposition that colour and me to be itself almost conclusive of ornament are strictly correlated with the whole matter at issue. Natural health, vigour, and general fitness to selection, or the survival of the fittest, survive. We have shown that there acts perpetually and on an enormous is reason to believe that this is the scale. Taking the offspring of each case, and if so, voluntary sexual sepair of birds as, on the average, only
lection becomes as unnecessary as it six annually, one-third of these at would certainly be ineffective. most will be preserved, while the two- There is one other very curious case thirds which are least fitted will die. of sexual colouring among birds—that, At intervals of a few years, whenever namely,in which the female is decidedly unfavourable conditions occur, five- brighter or more strongly marked than sixths, nine-tenths, or even a greater the male ; as in the fighting quails proportion of the whole yearly pro- (Turnix), painted snipe (Rhynchæa), duction are weeded out, leaving only two species of phalarope (Phalaropus), the most perfect and best adapted to and the common cassowary (Casuarius survive. Now unless these survivors galeatus). In all these cases, it is are on the whole the most ornamental, known that the males take charge of this rigid selective power must neu
and incubate the eggs,
while the tralise and destroy any influence that females are almost always larger and may be exerted by female selection. more pugnacious. In my “Theory For the utmost that can be claimed of Birds' Nests" (Natural Selection,
p. 251), I imputed this difference of been added, we find intensity and colour to the greater need for pro- variety of colour at its highest pitch tection by the male bird while in- among the South American buttercubating, to which Mr. Darwin has flies of the families Heliconida objected that the difference is not and Danaidæ, as well as among the sufficient, and is not always so dis- Nymphalidæ and Erycinidæ, many of tributed as to be most effective for which obtain the necessary protection this purpose, and he believes that it in other ways. Among birds also, is due to reversed sexual selection, wherever the habits are such that that is, to the female taking the usual no special protection is needed for the role of the male, and being chosen for females, and where the species freher brighter tints. We have already
We have already quent the depths of tropical forests reason for rejecting this latter and are thus naturally protected from theory in every case, and I also ad
Swoop of birds of prey, we find mit that my theory of protection is, almost equally intense coloration; as in this case, only partially if at all in the trogons, barbets, and gapers. applicable. But the general theory of Of the mode of action of the geneintensity of colour being due to general ral principles of colour-development vital energy is quite applicable ; and among animals, we have an excellent the fact that the superiority of the example in the humming-birds. Of female in this respect is quite excep- all birds these are at once the smallest, tional, and is therefore probably not the most active, and the fullest of vital of very ancient date in any one case, energy. When poised in the air their will account for the difference of wings are invisible, owing to the racolour thus produced being always pidity of their motion, and when comparatively slight.
startled they dart away with the ra
pidity of a flash of light. Such active Theory of Typical Colours. - The creatures would not be an easy prey to remaining kinds of animal colours
any rapacious bird; and if one at length those which can neither be classed was captured, the morsel obtained would as protective, warning, nor sexual, hardly repay the labour.
. We may be are for the most part readily ex- sure, therefore, that they are praeplained on the general principles of tically unmolested. The immense the development of colour which we variety they exhibit in structure, have now laid down. It is a most plumage, and colour, indicates a high suggestive fact, that, in cases where antiquity for the race, while their colour is required only as a warning, general abundance in individuals as among the uneatable caterpillars, shows that they are a
dominant we find, not one or two glaring tints group, well adapted to all the cononly but every kind of colour disposed ditions of their existence. Here we in elegant patterns, and exhibiting find everything necessary for the dealmost as much variety and beauty as velopment of colour and accessory among insects and birds. Yet here, plumes. The surplus vital energy not only is sexual selection out of the shown in their combats and es. question, but the need for recognition cessive activity, has expended itself and identification by others of the in ever-increasing developments of same species, seems equally unneces- plumage, and greater and greater in sary. We can then only impute this tensity of colour, regulated only by variety to the normal production of the need for specific identification colour in organic forms, when fully ex- which would be especially required posed to light and air and undergoing in such small and mobile creatures great and rapid developmental modi- Thus may be explained those remarkfication. Among more perfect animals, able differences of colour between where the need for recognition has closely - allied species, one having *