72 SEX 



CHAPTER IV 



THEORY OF SEX-DIMORPHISM 



Darwin's theory A Lamarckian theory Physiological 

 theories The role of internal secretions Sex-changes 

 in crabs Specific characters and sex-characters 

 Difficulty as to origins Suggestion as to the mode of 

 origin of sex-characters. 



DARWIN'S THEORY. As everyone knows, Dar- 

 win proposed a theory of sexual selection to 

 account for the frequent occurrence of secon- 

 dary sex characters, such as are familiar in 

 cases like stags, stag's-horn beetles, peacocks, 

 and birds of Paradise. On the one hand, he 

 pointed out, there are the combats between 

 rival males which tend to leave those with 

 less perfect weapons or less ability to use them 

 without their fair share in parentage. On 

 the other hand, there is preferential mating, 

 in the course of which the female chooses or 

 seems to choose the more decorative, or agile, 

 or melodious, or otherwise attractive suitor, 

 thus tending to increase these gifts and graces 

 in the hereditary equipment of the race, as 

 far at least as the male sex is concerned. 



There is considerable difficulty in regard to 

 the facts of the case. Where the weaker 

 males, worsted in combat, are killed, or ex- 

 pelled from the herd, or left unmated, the 

 elimination may be reasonably interpreted 

 as tending to raise the standard of those 

 qualities in virtue of which the successful 

 males succeeded. In some cases, however, 

 it is stated that the males unfortunate in war 

 are lucky in love. Much depends on the 



