adduced by Mr. Darwin in support of his theory of voluntary sexual selection.

are

In Descent of Man, 2nd ed., pp. 307-316, we find an elaborate account of the various modes of colouring of butterflies and moths, proving that the coloured parts are always more or less displayed, and that they have some evident relation to an observer. Mr. Darwin then says-"From the several foregoing facts it is impossible to admit that the brilliant colours of butterflies, and of some few moths, have commonly been acquired for the sake of protection. We have seen that their colours and elegant patterns arranged and exhibited as if for display. Hence I am led to believe that the females prefer or are most excited by the more brilliant males; for on any other supposition the males would, as far as we can see, be ornamented to no purpose" (l.c., p. 316). I am not aware that any one has ever maintained that the brilliant colours of butterflies have "commonly been acquired for the sake of protection," yet Mr. Darwin has himself referred to cases in which the brilliant colour is so placed as to serve for protection; as for example, the eye-spots on the hind wings of moths, which are pierced by birds and so save the vital parts of the insect, while the bright patch on the orange-tip butterflies which Mr. Darwin denies are protective, may serve the same purpose. It is in fact somewhat remarkable how very generally the black spots, ocelli, or bright patches of colour are on the tips, margins, or discs of the wings; and as the insects are necessarily visible while flying, and this is the time when they are most subject to attacks by insectivorous birds, the position of the more conspicuous parts at some distance from the body may be a real protection to them. Again, Mr. Darwin admits that the white colour of the male Ghost-moth may render it more easily seen by the female while flying about in the dusk, and if to this we add that it will be also more readily dis

tinguished from allied species, we have a reason for diverse ornamentation in these insects quite sufficient to account for most of the facts, without believing in the selection of brilliant males by the females, for which there is not a particle of evidence. The facts given to show that butterflies and other insects can distinguish colours and are attracted by colours similar to their own, are quite consistent with the view that colour, which continually tends to appear, is utilised for purposes of identification and distinction, when not required to be modified or suppressed for purposes of protection. The cases of the females of some species of Thecla, Callidryas, Colias, and Hipparchia, which have more conspicuous markings than the male, may be due to several causes: to obtain greater distinction from other species, for protection from birds, as in the case of the yellow-underwing moths, while sometimes-as in Hipparchiathe lower intensity of colouring in the female may lead to more contrasted markings. Mr. Darwin thinks that here the males have selected the more beautiful females, although one chief fact in support of his theory of voluntary sexual selection is, that throughout the whole animal kingdom the males are usually so ardent that they will ac cept any female, while the females are coy, and choose the handsomest males, whence it is believed the general brilliancy of males as compared with females has arisen.

Perhaps the most curious cases of sexual difference of colour are those in which the female is very much more gaily coloured than the male. This occurs most strikingly in some species of Pieris in South America, and of Diadema in the Malay islands, and in both cases the females resemble species of the uneatable Danaidæ and Heliconidæ, and thus gain a protection. In the case of Pieris pyrrha, P. malenka, and P. lorena, the males are plain white and black, while the females are orange, yellow, and black, and so banded and spotted as exactly to

resemble species of Heliconidæ. Mr. Darwin admits that these females have acquired these colours as a protection; but as there is no apparent cause for the strict limitation of the colour to the female, he believes that it has been kept down in the male by its being unattractive to her. This appears to me to be a supposition opposed to the whole theory of sexual selection itself. For this theory is, that minute variations of colour in the male are attractive to the female, have always been selected, and that thus the brilliant male colours have been produced. But in this case he thinks that the female butterfly had a constant aversion to every trace of colour, even when we must suppose it was constantly recurring during the successive variations which resulted in such a marvellous change in herself. But if we consider the fact that the females frequent the forests where the Heliconidæ abound, while the males fly much in the open, and assemble in great numbers with other white and yellow butterflies on the banks of rivers, may it not be possible that the appearance of orange stripes or patches would be as injurious to the male as it is useful to the female, by making him a more easy mark for insectivorous birds among his white companions? This seems a more probable supposition, than the altogether hypothetical choice of the female, sometimes exercised in favour of and sometimes against every new variety of colour in her partner.

The full and interesting account given by Mr. Darwin of the colours and habits of male and female birds (Descent of Man, chapters xiii. and xiv.), proves that in most, if not in all cases, the male birds fully display their ornamental plumage, before the females and in rivalry with each other; but on the essential point of whether the female's choice is determimed by minute differences in these ornaments or in their colours, there appears to be an entire absence of evidence. In the section on "Preference

for particular Males by the Females," the facts quoted show indifference to colour, except that some colour similar to their own seems to be preferred. But in the case of the hen canary, who chose a greenfinch in preference to either chaffinch or goldfinch, gay colours had evidently no preponderating attraction. There is some evidence adduced that female birds may, and probably do, choose their mates, but none whatever that the choice is determined by difference of colour; and no less than three eminent breeders informed Mr. Darwin that they "did not believe that the females prefer certain males on account of the beauty of their plumage." Again, Mr. Darwin himself 66 says: as a general rule colour appears to have little influence on the pairing of pigeons." The oftquoted case of Sir R. Heron's peahens which preferred an "old pied cock" to those normally coloured, is a very unfortunate one, because pied birds are just those that are not favoured in a state of nature, or the breeds of wild birds would become as varied and mottled as our domestic varieties. If such irregular fancies were not rare exceptions the production of definite colours and patterns by the choice of the female birds, or in any other way, would be impossible.

We now come to such wonderful developments of plumage and colour as are exhibited by the peacock and the Argus-pheasant; and I may here mention that it was the case of the latter bird, as fully discussed by Mr. Darwin, which first shook my belief in "sexual," or more properly "female" selection. The long series of gradations, by which the beautifully shaded ocelli on the secondary wingfeathers of this bird have been produced, are clearly traced out, the result being a set of markings, so exquisitely shaded as to represent "balls lying loose within sockets,"-purely artificial objects of which these birds could have no possible knowledge. That this result should have been attained through thousands and tens

of thousands of female birds all preferring those males whose markings varied slightly in this one direction, this uniformity of choice continuing through thousands and tens of thousands of generations, is to me absolutely incredible. And, when further, we remember that those which did not so vary would also, according to all the evidence, find mates and leave offspring, the actual result seems quite impossible of attainment by such

means.

Without pretending to solve completely so difficult a problem, I would point out a circumstance which seems to afford a clue. It is, that the most highly-coloured and most richlymost richlyvaried markings, occur on those parts of the plumage which have undergone the greatest modification, or have acquired the most abnormal development.

In the peacock, the tail-coverts are enormously developed, and the "eyes are situated on the greatly dilated ends. In the birds of paradise, breast, or neck, or head, or tailfeathers, are greatly developed and highly coloured. The hackles of the cock, and the scaly breasts of humming-birds are similar developments; while in the Argus-pheasant the secondary quills are so enormously lengthened and broadened as to have become almost useless for flight. Now it is easily conceivable, that during this process of development, inequalities in the distribution of colour may have arisen in different parts of the same feather, and that spots and bands may thus have become broadened out into shaded spots or ocelli, in the way indicated by Mr. Darwin, much as the spots and rings on a soap bubble increase with increasing tenuity. This is the more probable, as in domestic fowls varieties tend to become symmetrical, quite independently of sexual selection. (Descent of Man, p. 424.)

If now we accept the evidence of Mr. Darwin's most trustworthy correspondents, that the choice of the female, so far as she exerts any, falls

upon the "most vigorous, defiant, and mettlesome male e; " and if we further believe, what is certainly the case, that these are as a rule the most brightly coloured and adorned with the finest developments of plumage, we have a real and not a hypothetical cause at work. For these most healthy, vigorous, and beautiful males will have the choice of the finest and most healthy females, will have the most numerous and healthy families, and will be able best to protect and rear those families. Natural selection, and what may be termed male selection, will tend to give them the advantage in the struggle for existence, and (thus the fullest plumage and the finest colours will be transmitted, and tend to advance in each succeeding genera tion.

There remains, however, what Mr. Darwin evidently considers his strongest argument the display by the male of each species of its peculiar beauties of plumage and colour. We have here, no doubt, a very remarkable and very interesting fact but this too may be explained by general principles, quite independent of any choice or volition of the female bird. During pairing-time, the male bird is in a state of great excitement, and full of exuberant energy. Even unornamented birds flutter their wings or spread them out, erect their tails or crests, and thus give vent to the nervous excitability with which they are overcharged. It is not improbable that crests and other erectile feathers may be primarily of use in frightening away enemies, since they are generally erected when angry or during combat. Those individuals who were most pugnacious and defiant, and who brought these erectile plumes most frequently and most powerfully into action, would tend to increase them by use, and to leave them further developed in some of their descendants. If, in the course of this development, colour appeared, we have every reason to believe it would be most vivid in these most pugnacious and energetic

individuals, and as these would always have the advantage in the rivalry for mates (to which advantage the excess of colour and plumage might sometimes conduce), there seems nothing to prevent a progressive development of these ornaments in all dominant races, that is, wherever there was such a surplus of vitality, and such complete adaptation to conditions, that the inconvenience or danger produced by them, was so comparatively small as not to affect the superiority of the race over its nearest allies. If then those portions of the plumage, which were originally erected and displayed, became developed and coloured, the actual display, under the influence of jealousy or sexual excitement becomes intelligible.

The males, in their rivalry with each other, would see what plumes were most effective, and each would endeavour to excel his enemy as far as voluntary exertion could effect it, just as they endeavour to rival each other in song, even sometimes to the point of causing their own destruction.

There is also a general argument against Mr. Darwin's views on this question, founded on the nature and potency of "natural" as opposed to

sexual" selection, which appears to me to be itself almost conclusive of the whole matter at issue. Natural selection, or the survival of the fittest, acts perpetually and on an enormous scale. Taking the offspring of each pair of birds as, on the average, only six annually, one-third of these at most will be preserved, while the twothirds which are least fitted will die. At intervals of a few years, whenever unfavourable conditions occur, fivesixths, nine-tenths, or even a greater proportion of the whole yearly production are weeded out, leaving only the most perfect and best adapted to survive. Now unless these survivors are on the whole the most ornamental, this rigid selective power must neutralise and destroy any influence that may be exerted by female selection. For the utmost that can be claimed

for this is, that a small fraction of the least ornamented do not obtain mates, while a few of the most ornamented may leave more than the average number of offspring. Unless, therefore, there is the strictest correlation between ornament and general perfection, the former can have no permanent advantage; and if there is (as I maintain) such a correlation, then the sexual selection of ornament for which there is little or no evidence becomes needless, because natural selection which is an admitted vera causa will itself produce all the results. In the case

of butterflies the argument becomes even stronger, because the fertility is so much greater, and the weeding out of the unfit takes place, to a great extent, in the egg and larvæ state. Unless the eggs and larva which escaped to produce the next generation were those which would produce the more highly-coloured butterflies, it is difficult to perceive how the slight preponderance of colour sometimes selected by the females, should not be wholly neutralised by the extremely rigid selection for other qualities to which the offspring in every stage are exposed. The only way in which we can account for the observed facts is, by the supposition that colour and ornament are strictly correlated with health, vigour, and general fitness to survive. We have shown that there is reason to believe that this is the case, and if so, voluntary sexual selection becomes as unnecessary as it would certainly be ineffective.

There is one other very curious case of sexual colouring among birds-that, namely,in which the female is decidedly brighter or more strongly marked than the male; as in the fighting quails (Turnix), painted snipe (Rhynchæa), two species of phalarope (Phalaropus), and the common cassowary (Casuarius galeatus). In all these cases, it is known that the males take charge of and incubate the eggs, while the females are almost always larger and more pugnacious. In my "Theory of Birds' Nests" (Natural Selection,

p. 251), I imputed this difference of colour to the greater need for protection by the male bird while incubating, to which Mr. Darwin has objected that the difference is not sufficient, and is not always so distributed as to be most effective for this and he believes that it purpose, is due to reversed sexual selection, that is, to the female taking the usual rôle of the male, and being chosen for her brighter tints. We have already seen reason for rejecting this latter theory in every case, and I also admit that my theory of protection is, in this case, only partially if at all applicable. But the general theory of intensity of colour being due to general vital energy is quite applicable; and the fact that the superiority of the female in this respect is quite exceptional, and is therefore probably not of very ancient date in any one case, will account for the difference of colour thus produced being always comparatively slight.

Theory of Typical Colours. - The remaining kinds of animal coloursthose which can neither be classed as protective, warning, nor sexual, are for the most part readily explained on the general principles of the development of colour which we have now laid down. It is a most suggestive fact, that, in cases where colour is required only as a warning, as among the uneatable caterpillars, we find, not one or two glaring tints only but every kind of colour disposed in elegant patterns, and exhibiting almost as much variety and beauty as among insects and birds. Yet here, not only is sexual selection out of the question, but the need for recognition and identification by others of the same species, seems equally unnecessary. We can then only impute this variety to the normal production of colour in organic forms, when fully exposed to light and air and undergoing great and rapid developmental modification. Among more perfect animals, where the need for recognition has

been added, we find intensity and variety of colour at its highest pitch among the South American butterflies of the families Heliconidæ and Danaidæ, as well as among the Nymphalidæ and Erycinidæ, many of which obtain the necessary protection in other ways. Among birds also, wherever the habits are such that no special protection is needed for the females, and where the species frequent the depths of tropical forests and are thus naturally protected from the swoop of birds of prey, we find almost equally intense coloration; as in the trogons, barbets, and gapers.

Of the mode of action of the general principles of colour-development among animals, we have an excellent example in the humming-birds. Of all birds these are at once the smallest, the most active, and the fullest of vital energy. When poised in the air their wings are invisible, owing to the ra pidity of their motion, and when startled they dart away with the rapidity of a flash of light. Such active creatures would not be an easy prey to any rapacious bird; and if one at length was captured, the morsel obtained would hardly repay the labour. We may be sure, therefore, that they are praetically unmolested. The immense

variety they exhibit in structure, plumage, and colour, indicates a high antiquity for the race, while their general abundance in individuals shows that they are a dominant group, well adapted to all the conditions of their existence. Here we find everything necessary for the development of colour and accessory plumes. The surplus vital energy shown in their combats and excessive activity, has expended itself in ever-increasing developments of plumage, and greater and greater intensity of colour, regulated only by the need for specific identification which would be especially required in such small and mobile creatures. Thus may be explained those remarkable differences of colour between closely allied species, one having a