106 THE THEORIES OF EVOLUTION 



males, were more in need of distinctive characters 

 which would enable the males to recognise them. 



There is also a theory according to which certain 

 useless characters like the huge antlers of old stags, 

 result from a desire on the part of the males to appear 

 more dangerous to their rivals than they are in re- 

 ality, but this is an assumption at least as gratuitous 

 as the theory of the selection by the females. 



Another idea, more plausible, and suggested inci- 

 dentally by Darwin, is that those males which bear 

 ornamental characters possess a surplus of energy 

 which reveals itself through certain structures such as 

 a deeper pigmentation or an abundance of feathers. 

 Their various special motions or dances would only 

 be the consequence of a marked sexual excitation. 

 This explanation is unconvincing for it does not ex- 

 plain how a surplus of energy could produce, for in- 

 stance, a brighter colouring. 



According to another theory which seems to point 

 at last in the right direction and which has many 

 points in common with the preceding one, second- 

 ary sexual characters can be traced directly to certain 

 conditions of the sexual organs, being due to internal 

 secretions which act upon the tissues of the organism. 

 Emery was the first to offer this explanation. 9 Va- 

 rious experiments have demonstrated the fact that the 



» Gedanken zur Descendenz-und Vererbungtheorie. (Biologisches Cen- 

 tralblatt, 1903, pp. 397-420.) 



