CHAPTER VI 



DARWIN'S THEORY OF SEXUAL SELECTION 



Sexual Selection 



The theory of sexual selection was formulated by Darwin, 

 even in the first edition of the " Origin of Species," but was 

 developed at much greater length in " The Descent of Man." 

 " This form of selection depends, not on a struggle for exist- 

 ence in relation to other organic beings or to external condi- 

 tions, but on a struggle between the individuals of one sex, 

 generally the males, for the possession of the other sex. The 

 result is not death to the unsuccessful competitor, but few or 

 no offspring. Sexual selection is, therefore, less rigorous 

 than natural selection. Generally the most vigorous males, 

 those which are best fitted for their place in nature, will leave 

 most progeny. But in many cases victory depends, not so 

 much on general vigor, as on having special weapons, con- 

 fined to the male sex. A hornless stag or spurless cock 

 would have a poor chance of leaving numerous offspring. 

 Sexual selection, by always allowing the victor to breed, 

 might surely give indomitable courage, length to the spur, 

 and strength to the wing to strike in the spurred leg in 

 nearly the same manner as the brutal cock-fighter by the 

 careful selection of his best cocks." It is important to no- 

 tice that the theory of sexual selection is admittedly an 

 extension of the selection principle into a new field. Having 

 accounted for domesticated animals and plants by artificial 

 selection, and for the adaptations of wild species by natural 

 selection, there remained only to account for the second- 



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