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Show 182 SEXUAL SELECTION: BIRDS. PART II. for some distinct purpose, perhaps for gaining a warmer winter covering ; and that variations in the plumage occurring during the summe~ were accumulate~ through sexual selection, and transmitted to the offsprmg at the same season of the year. Such variations being inherited either by both sexes or by the males alone, according to the form of inheritance which prevailed. This appears more probable than that. these. species in all cases originally tended to retam the1r ornament~! plumage during the winter, but were saved from th1s through natural selection, owing to the inconvenience or danger thus caused. I have endeavoured in this chapter to shew that the arguments are not trustworthy in favour of the view that weapons, bright colours, and various ornaments, are now confined to the males owing to the conversion, by means of natural selection, of a tendency to tho equal transmission of characters to both sexes into transmission to the male sex alone. It is also doubtful whether tho colours of many female birds are clue to the preservation, for the sake of protection, of variations which were from the first limited in their transmission to the female sex. But it will be convenient to defer any further discussion on this subject until I treat, in the following chapter, on the differences in plumage between the young and old. C HAP. XVI. INHERITANCE, LIMITED BY .AGE. 183 CHAPTER XVI. BIRDS-concluded. 'The immature plumage in relation to the character of the plumaae in both sexes when adult- Six classes of cases- Sexual diffe~·ences between the males of closely-allied or representative species -The female assuming the characters of the male- Pluma"e of the young in relation to the summer and winter plumage ot the 11dults -On the increase of beauty in the Birds of the WorldProtective colouring- Conspicuously-coloured birds- Novelty appreciated- Summary of the four chapterR on Birds. WE must now consider the transmission of cha1·acters as limited by age in reference to sexual selection. The truth and importance of the principle of inheritance at corresponding ages need not here be discussed, as enough bas aheady been said on the subject. Before giving the several rather complex rules or classes of cases, under which all the differences in plumage between the young and the old, as far as known to me, may be included, it will be well to make a few preliminary remarks. Vritb animals of all kinds when the young differ in colour from the adults, and the colours of the former are not, as far as we can see, of any special service, they may generally be attributed, like various embryological structures, to the retention by the young of the character (){an early progenitor. But this view can be maintained with confidence, only when the young of several species dosely resemble each other, and likewise resemble other adult species belonging to the same group; fo1· th~ latter are the living proofs that such a state of tlungs was formerly possible. Young lions and pumas |
