284 Journal of Travel and Natural History 



colours, that the normal action of sexual selection is to develop 

 colour and beauty in both sexes by the preservation and multipli- 

 cation of all varieties of colour in either sex which are pleasing to 

 the other. The female bird, however, while sitting on her eggs in 

 an uncovered nest, is especially open to the attacks of enemies, 

 and any modification of colour which rendered her more con- 

 spicuous would lead to her destruction and that of her offspring. 

 All variations of colour in this direction in the female would, there- 

 fore, sooner or later be exterminated, while such modifications as 

 rendered her inconspicuous by assimilating her to surrounding 

 objects, as the earth or the foliage, would, on the whole, be pre- 

 served the longest, and thus lead to the attainment of those 

 brown or green and inconspicuous tints which form the colouring 

 (of the upper surface at least) of the vast majority of female birds 

 which sit upon open nests." 



Let us now analyze the assumptions which are involved in this 

 theory of the physical causes, whereby opposite systems of colouring 

 have been produced in birds. 



It assumes that there is some innate tendency in the plumage of 

 all hen birds, or at least of the hens of certain species of birds, to 

 become as brilliantly coloured as the cock. It assumes, in the 

 second place, that this colouring, when produced, is always more 

 pleasing to the other sex than dull colouring. It assumes, for ex- 

 ample, that a cock Pheasant would be much better pleased if he 

 could have a wife coloured like himself than a wife coloured like 

 the ground — an assumption which, by analogy, as applied to our 

 own species, would require that men ought to prefer for wives 

 the most masculine-looking women. It assumes, in the third 

 place, that this innate tendency to the development of bright 

 colours has no other limit than the extermination of the unfortunate 

 hens on which it is exerted. It assumes, in the fourth place, that 

 somehow, as these individual bright hens come to be all killed off, 

 this dangerous tendency gets so snubbed and discouraged in some 

 other individuals that it ceases to act upon them. It assumes, in 

 the fifth place, that alongside of this tendency to produce bright hues 

 there is all the time another tendency opposite but equally innate 

 to produce dull colouring, imitative of the colours of the ground or 

 of the habitat of the bird. It assumes, in the sixth place, that this 

 opposite tendency of colouring becomes encouraged and confirmed 

 in certain individuals by some kind of knowledge or intimation con- 

 veyed to it, that the birds upon which it works have a better chance 



