The Descent of Man, and Selection in Relation to Sex. Charles Darwin

characters are absent in the lowest classes—Brilliant colours—Mollusca—Annelids—Crustacea, secondary sexual characters strongly developed; dimorphism; colour; characters not acquired before maturity—Spiders, sexual colours of; stridulation by the males—Myriapoda.

      X. — Secondary Sexual Characters of Insects.

      Diversified structures possessed by the males for seizing the females—Differences between the sexes, of which the meaning is not understood—Difference in size between the sexes—Thysanura—Diptera—Hemiptera—Homoptera, musical powers possessed by the males alone—Orthoptera, musical instruments of the males, much diversified in structure; pugnacity; colours—Neuroptera, sexual differences in colour—Hymenoptera, pugnacity and odours—Coleoptera, colours; furnished with great horns, apparently as an ornament; battles; stridulating organs generally common to both sexes.

XI.

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      Insects, continued.—Order Lepidoptera.

      (Butterflies and Moths.)

      Courtship of Butterflies—Battles—Ticking noise—Colours common to both sexes, or more brilliant in the males—Examples—Not due to the direct action of the conditions of life—Colours adapted for protection—Colours of moths—Display—Perceptive powers of the Lepidoptera—Variability—Causes of the difference in colour between the males and females—Mimicry, female butterflies more brilliantly coloured than the males—Bright colours of caterpillars—Summary and concluding remarks on the secondary sexual character of insects—Birds and insects compared.

XII.

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      Secondary Sexual Characters of Fishes, Amphibians, and Reptiles.

      Fishes: Courtship and battles of the males—Larger size of the females—Males, bright colours and ornamental appendages; other strange characters—Colours and appendages acquired by the males during the breeding-season alone—Fishes with both sexes brilliantly coloured—Protective colours—The less conspicuous colours of the female cannot be accounted for on the principle of protection—Male fishes building nests, and taking charge of the ova and young. AMPHIBIANS: Differences in structure and colour between the sexes—Vocal organs. REPTILES: Chelonians—Crocodiles—Snakes, colours in some cases protective—Lizards, battles of—Ornamental appendages—Strange differences in structure between the sexes—Colours—Sexual differences almost as great as with birds.

XIII.

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      Secondary Sexual Characters of Birds.

      Sexual differences—Law of battle—Special weapons—Vocal organs—Instrumental music—Love-antics and dances—Decorations, permanent and seasonal—Double and single annual moults—Display of ornaments by the males.

      XIV. — Birds—continued.

      Choice exerted by the female—Length of courtship—Unpaired birds—Mental qualities and taste for the beautiful—Preference or antipathy shewn by the female for particular males—Variability of birds—Variations sometimes abrupt—Laws of variation—Formation of ocelli—Gradations of character—Case of Peacock, Argus pheasant, and Urosticte.

      XV. — Birds—continued.

      Discussion as to why the males alone of some species, and both sexes of others are brightly coloured—On sexually-limited inheritance, as applied to various structures and to brightly-coloured plumage—Nidification in relation to colour—Loss of nuptial plumage during the winter.

XVI.

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      Birds—concluded.

      The immature plumage in relation to the character of the plumage in both sexes when adult—Six classes of cases—Sexual differences between the males of closely-allied or representative species—The female assuming the characters of the male—Plumage of the young in relation to the summer and winter plumage of the adults—On the increase of beauty in the birds of the world—Protective colouring—Conspicuously coloured birds—Novelty appreciated—Summary of the four chapters on birds.

XVII.

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      Secondary Sexual Characters of Mammals.

      The law of battle—Special weapons, confined to the males—Cause of absence of weapons in the female—Weapons common to both sexes, yet primarily acquired by the male—Other uses of such weapons—Their high importance—Greater size of the male—Means of defence—On the preference shewn by either sex in the pairing of quadrupeds.

XVIII.

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      Secondary Sexual Characters of Mammals—continued.

      Voice—Remarkable sexual peculiarities in seals—Odour—Development of the hair—Colour of the hair and skin—Anomalous case of the female being more ornamented than the male—Colour and ornaments due to sexual selection—Colour acquired for the sake of protection—Colour, though common to both sexes, often due to sexual selection—On the disappearance of spots and stripes in adult quadrupeds—On the colours and ornaments of the Quadrumana—Summary.

SEXUAL SELECTION IN RELATION TO MAN, AND CONCLUSION.

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      XIX. — Secondary Sexual Characters of Man.

      Differences between man and woman—Causes of such differences, and of certain characters common to both sexes—Law of battle—Differences in mental powers, and voice—On the influence of beauty in determining the marriages of mankind—Attention paid by savages to ornaments—Their ideas of beauty in women—The tendency to exaggerate each natural peculiarity.

      XX. — Secondary Sexual Characters of Man—continued.

      On the effects of the continued selection of women according to a different standard of beauty in each race—On the causes which interfere with sexual selection in civilised and savage nations—Conditions favourable to sexual selection during primeval times—On the manner of action of sexual selection with mankind—On the women in savage tribes having some power to choose their husbands—Absence of hair on the body, and development of the beard—Colour of the skin—Summary.

XXI.

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      General Summary and Conclusion.

      Main conclusion that man is descended from some lower form—Manner of development—Genealogy of man—Intellectual and moral faculties—Sexual selection—Concluding remarks.

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