The Making of Species 



explanation of all the peculiarities of animal 

 structure and colouration. 



It is not easy to understand how natural selec- 

 tion can have caused marked sexual dimorphism 

 in a species where the habits of the sexes are 

 the same, in the Paradise Flycatcher ( Terpsiphone 

 paradisi), for example, where the cock and the 

 hen obtain their food in the same way, and share 

 equally the duties of nest-building, incubation, and 

 feeding the young. 



Of course, in all species where each individual 

 carries only one of the two kinds of sexual organs, 

 there must of necessity be some slight difference 

 between the individuals that carry the male organ, 

 which performs one function, and those that carry 

 the female organ, which performs another function. 



But in many species the sexes display differ- 

 ences which have no direct connection with the 

 generative organs for example, the deer, where 

 the stag alone has horns. 



Those characters which differ with the sex, 

 but are not directly connected with the organs 

 of reproduction, are known as secondary sexual 

 characters. 



In nearly all species where the male and 

 female differ in beauty, it is the male who 

 surpasses the female. Natural selection is, 

 in many cases, not able to explain the origin 

 of these differences, or why, when they occur, 

 the male should be more beautiful than the 



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