xni EXTENSIONS OF DARWINISM 261 



of the teeth, which are wonderfully varied throughout the 

 whole of the vertebrate sub-kingdom. Yet the more or less 

 use of the teeth cannot be shown to have any tendency to 

 change their form or structure in the special ways in which 

 they have been again and again changed, though it might 

 possibly have induced growth and increased size. Yet again, 

 the scales or plates of reptiles, the feathers of birds, and the 

 hairy covering of mammals, have never been shown to have 

 their special textures, shapes, or density modified by the 

 mere act of use. One common error is that cold produces 

 length and density of hair, heat the reverse ; but the purely 

 tropical monkey-tribe are, as a rule, quite as well clothed 

 with dense fur as most of the temperate or arctic mammals 

 while no birds are more luxuriantly feather-clad than those 

 of the tropics. Neither is it certain that increased gazing 

 improves the eyes, or loud noises the ears, or increased 

 eating the stomach ; so that we must conclude that this aid 

 to the powers of natural selection is very partial in its 

 action, and that it has no claim to the important position 

 sometimes given it. 



(3) Germinal Selection, an Important Extension of the 

 Theory of Natural Selection 



Although I was at first inclined to accept Darwin's view 

 of the influence of female choice in determining the develop- 

 ment of ornamental colour or appendages in the males, yet, 

 when he had adduced his wonderful array of facts bearing 

 upon the question in the Descent of Man, the evidence for 

 any such effective choice appeared so very scanty, and the 

 effects imputed to it so amazingly improbable, that I felt 

 certain that some other cause was at work. In my Tropical 

 Nature (1878) and in my Darwinism (1889) I treated the 

 subject at considerable length, adducing many facts to prove 

 that, even in birds, the colours and ornamental plumes of 

 the males were not in themselves attractive, but served 

 merely as signs of sexual maturity and vigour. In the case 

 of insects, especially in butterflies, where the phenomena of 

 colour, and to some extent of ornament, are strikingly 

 similar to those of birds, the conception of a deliberate 

 aesthetic choice, by the females, of the details of colour, 



