SEXUAL SELECTION. 



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species that may be encountered, while they are said 

 even to attack birds of prey that approach too closely 

 to their nests. It must be admitted that these facts 

 agree well with the theory that colour and ornament 

 are due to surplus vital energy and a long course of 

 unchecked development. We have also direct evidence 

 that the males are more active and energetic than the 

 females. Mr. Gosse says that the whirring made by 

 the male Polytmus humming-bird is shriller than that 

 produced by the female ; and he also informs us that 

 the male flies higher and frequents mountains while the 

 female keeps to the lowlands. 



Theory of Typical Colours. — The remaining kinds of 

 animal colours, those which can neither be classed as 

 protective, warning, or sexual, are for the most part 

 readily explained on the general principles of the de- 

 velopment 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 under- 

 going great and rapid developmental modification. 

 Among more perfect animals, where the need for recog- 

 nition has been added, we find intensity and variety of 

 colour at its highest pitch among the South American 



