Descent Of Man Research Articles

The Descent of Man, and Selection in relation to Sex

II. THAT selection in relation to sex has been an important factor in the formation of the present breeds of animals was more than indicated in the “Origin of Species,“and the theory has since been especially worked out by Professor Haeckel. It includes two distinct hypotheses. One is that in contests between males, the weakest would go to the wall, and thus either be killed outright, or at least debarred more or less completely from transmitting their characters to another generation. This may be regarded as a particular case of Natural Selection, and may be compared with the theory of protection by mimicry, suggested by Mr. Bates, and carried out by him and by Mr. Wallace. But though in the lists of Love the battle is often to the strong, even more frequently it is to the beautiful. This introduces a new process, of which the effects are not nearly so obvious as those of Natural Selection, either in its simplest form or in the more complicated cases of mimicry, and of sexual selection by battle. Many circumstances must combine in order that the most successful wooers shall have a larger and more vigorous progeny than the rest. In the first place, all hermaphrodite and all sessile animals may be excluded, and also those cases in which sexual differences depend on different habits of life. Mr. Darwin then shows that secondary sexual characters are eminently variable, and that males vary more than females from the standard of the species, a standard determined by the young, by allied forms, and sometimes by the character of the male himself when his peculiar functions are only periodical, or when they have been artificially prevented. Moreover it is the males who take the active part in pairing, and who not only fight for the possession of their mates, but display their colours, their voice, or whatever be their peculiar attractions, in order to gain the same end. This rule is confirmed by the exceptional case of the cassowary and a few other species in which the hens court the male birds, fight together in rivalry, and accordingly assume the brighter colours and more attractive shape usually worn by the male. Not only the parental and incubating instincts, but the usual moral qualities of the two sexes are in these cases reversed: "the females being savage, quarrelsome, and noisy, the males gentle and good.“But it is further necessary to show that the females exert a choice among the males, and that the latter are polygamous, or arrive earlier at the place of pairing, as is the case with some birds, or else exceed in numbers, at least when both sexes are mature. On this point a series of observations is recorded relating chiefly to man, to domesticated mammals, and to insects. The rule as to transmission of male characters to both sexes appears.to be that when variations appear late in life they are usually developed in the same sex only of the next generation, although they are, of course, transmitted in a latent condition through both; while, on the other hand, the differences which appear before maturity in the parent are equally developed in both sexes when transmitted to the offspring. The numerous apparent exceptions to these laws of inheritance and of sexual selection are examined with wonderful fairness and fertility in resource. I may particularly refer to the discussion of the ways in which the young and adults of both sexes differ among birds. The extreme intricacy of some of the questions considered is best shown by a postscript in which, with characteristic candour, the author corrects "a serious and unfortunate error“in the eighth chapter. The Descent of Man, and Selection in relation to Sex. By Charles Darwin., &c. In two volumes. Pp. 428, 475. (Murray, 1871.)

The “Times” Review of Darwin's “Descent of Man”

THE British public are deeply indebted to the Times Reviewer for his very comforting and reassuring remarks on Mr. Darwin's “Descent of Man,” in which he has so well exposed the “utterly unsupported hypotheses,” the “unsubstantial presumptions,” the “cursory investigations,” of that “reckless” and “unscientific” writer. It is a great satisfaction to find that Mr. Darwin's odious conclusion that the genealogy of the Talbots, and the Howards, and the Percys must be traced back beyond the Conqueror to an Anthropomorphous Ape, and beyond the ape to an Acephalous Mollusk, rests on no logical foundation whatever. The Reviewer well suggests that anything so odious in idea, so immoral in its apparent tendency, and so different from what we have been accustomed to believe, cannot possibly be true. One is so glad indeed to be free once and for ever from the mischievous influence of such, “unpractical,” “disintegrating speculations,” that it seems worth while trying, if space can be found for the experiment, to elicit from the good nature of the Reviewer, or of those who think with him, a little clearer explanation here and there, before the subject is finally consigned to a well-merited oblivion.

Ape Resemblances to Man

THE Zoological Society can hardly fail to derive decided material advantage from the publication of Mr. Darwin's “Descent of Man.” It has been said that already there is a perceptible increase in the visitors to the monkey-house, though an early spring has no doubt co-operated with scientific zeal in the promotion of pilgrimages to the Regent's Park, undertaken in the interest of a more than Chinese worship of ancestors. These visits would, perhaps, be considerably increased if it were very widely known that a fine specimen of a closely-related structural ally was there to be seen and heard, and one the resemblance of which to us has, 1 venture to think, not been generally appreciated sufficiently. I allude to the fine specimen of the Hoolock Gibbon which has been some time at the Gardens, and which appears to rejoice in good health, good temper, and good voice.

Sexual Selection

MR. DARWIN in his recent work on the “Descent of Man has shown that throughout the animal kingdom the male generally displays the stronger passions and is always the most eager. The males, moreover, whenever secondary sexual characters occur, are, as a rule, the possessors of weapons for defence or offence, brilliant colours, or other ornamental appendages, all of which Mr. Darwin supposes to have been acquired through sexual selection, either for the purpose of charming the female or for struggling with other males for the possession of the females. In a few exceptional cases among birds, the females are the wooers, and these are then more brilliantly coloured than the males. In Westwood's work on insects* I met with the following passage:—“M. Donzel has published a curious memoir upon the flight of butterflies whilst coupling (Ann. Soc. Ent. de France, 1837, P. 77.) showing that whilst the males of Pontia Brassicæ, &c., Colias, and Polyommatus support the females, it is the latter which support their partners in the genera Thais, Thecla, Argynnis, Melitæa, Hipparchia, and Pieris.” Now this is strictly analogous to these exceptional birds, because, among our British representatives of these genera whenever a considerable sexual difference of colour occurs, the female is always the more brilliantly coloured. Thus, the female Thecla Quercus has the bright purple patch, and the female Thecla Betulæ the brilliant orange blotch on the fore wing, while the females of Hipparchia (Satyrus), Janira, and H. Semele are considerably brighter than their partners. The female H. Megæra is rather brighter than the male, and the same is true of Colias Edusa and C. Hyale, since the females of these species have orange or yellow spots in the black marginal border, represented in the males by thin streaks only. The females of the whole genus Pieris also are ornamented with black spots on the fore wings, which are only partially present in the males. I must confess that I am not convinced of the action of sexual selection in producing the colours of insects, but it cannot be denied that these facts are strikingly corroborative of Mr. Darwin's views. With few exceptions the rule holds good throughout the exotic species of these genera.

Sexual Selection

IN the first volume of “The Descent of Man,” at page 396, Mr Darwin says, referring to butterflies, that “the lower surface (of the wings) generally affords to entomologists the most useful character for detecting the affinities of the various species.” I think, also, that this lower surface might afford another link in the chain of argument by which Mr. Darwin supports his theory of Sexual Selection. Thus, for example, to speak of British species only, in the cabbage butterflies, the under surface of the wings is alike in both sexes of Pieris Brassicæ. The black spots, however, which appear on both surfaces of the fore wing of the female vanish from the upper surface of that of the male, probably because the female has some dislike to them. There is no difference in food-plant, habit, or need of protection here; the only explanation seems to be a whim of the female or a whim of nature, and we have lately discarded all thought of nature being freakish. In P. Rapæ and P. Napi a similar difference prevails, though less constant and in a degree less marked. In the allied Anthocharis Cardamines the under surface of both sexes is alike, notwithstanding the vast difference of their upper surfaces. When these butterflies alight and close their wings, the under surfaces of the hind wings are alone visible, and these are, apparently, the parts of the insect modified for the sake of protection. The simple yellow in Brassicæ and Rapæ, the green-veined yellow in Napi, the green marbling in Cardamines, of the under sides of the hind wings, are well fitted to conceal those insects as they settle on the wild flowers which they prefer.