CHAPTER X 



SEXUAL SELECTION, ASSORTATIVE MATING AND 

 THE DIFFERENTIAL MARRIAGE RATE 



"She's that sort," declared my Emma. "When you get them slim 

 maidens, so quick-eared and quick-eyed as a mouse, with full lips 

 that move and twinkle to their thoughts, and pretty, sly, sleepy eyes, 

 same as Phillipa have got, then you can take it that men interest 'em 

 more than any created thing. And they interest men, because nothin's 

 so lightning quick as a man to answer that sort of a signal." Eden 

 Phillpotts, Chronicles of St. Tid. 



As is well known Mr. Darwin attempted to explain the develop- 

 ment of many of the secondary sexual characters which distin- 

 guish the males from the females of higher animals as the result of 

 the action of sexual selection. This term was used by Darwin to 

 describe two very different kinds of selective activity; in one the 

 outcome was based upon the "law of battle" or the struggle 

 between rival males, the female falling as a matter of course to the 

 lot of the victor; in the other mode of selection, the female is 

 supposed to choose from among rival suitors the one whose 

 charms make the strongest appeal. The law of battle is essen- 

 tially a form of natural selection, although it does not as a rule 

 result in the actual death of the unsuccessful contestant. It offers 

 a very plausible explanation of the development of horns, tusks, 

 greater strength and various offensive and defensive features that 

 characterize the male sex of many animals. These endowments 

 are directly useful in keeping the stock of their possessors, if not 

 their possessors themselves, from extinction, and their develop- 

 ment would naturally be favored by selection. But with sexual 

 selection of the other type in which female volition forms an 

 essential element, the outcome is usually the development of 

 characteristics that charm the senses instead of directly aiding 



