1 68 PROBLEMS OF EVOLUTION 



receive such a blow in a book named after Darwin as a testimony 

 of respect. For the thrust, if only driven home, must prove mortal. 

 A great principle, if it operates only partially, must be unsound. 

 A law of gravitation to which some substances were subject but 

 not others would be a subject for ridicule. And no less so in the 

 case of Natural Selection : if it is a true principle, it must operate 

 wherever life is : it must decide the fate of every organism and 

 of every important part of every organism. Each structure must 

 pass muster either as definitely serviceable or as too insignificant 

 to be harmful. 



I have called attention early in this chapter to the fact that the 

 male sex is characterised by energy and variability, while the 

 female sex is less variable and comparatively sedentary. This 

 differentiation seems to date from the time when sexual dimorph- 

 ism originated, and it is the tendency of the male to vary, which 

 Sexual Selection has turned to account. It was there before any 

 of the conspicuous secondary characters of sex had been evolved. 

 Thus much may be conceded. There was material ready to 

 work upon. There was all the vigour which Dr Russel Wallace 

 assumes. But something more than this is wanted, some principle 

 that will account for the accumulation of favourable variations as 

 they arose. And none has been suggested except Sexual Selec- 

 tion. 



Sexual Moreover, Sexual Selection rightly understood, does not con- 

 Selection fli ct w jth Natural Selection, but leaves it in its supreme position, 

 ates with The secondary male characters, even if they lose some strong 

 Natural individual his life, are yet advantageous to the species. For by 

 captivating the hen birds, they help to bring it about that the 

 very cream of the males are the sires of all the next generation. 

 Thus vigour and not in the form ot showiness is transmitted 

 to the females, who have to rear and defend the young. The 

 courage with which a mother bird defends her nestlings is derived 

 from the line of pugnacious males from which she is sprung. 

 Thus the species gains by what might appear mere dandified 

 adornment and a mere fire-eating spirit. 



Natural Selection, as I have shown in the preceding chapter, 

 can only bring about further evolution when there is a change of 



