SEXUAL SELECTION. I45 



morphological constituents, single parts and organs may 

 be modified and perfected in definite advantageous direc- 

 tions, so as to secure for the race and species a higher 

 position in the surrounding world. 



Besides the general results of the right of the strong- 

 est, another very influential phenomenon comes into play 

 where the desire for propagation is concerned, which Dar- 

 win has designated as " sexual selection," and elaborated 

 in great detail in his work on the " Descent of Man." 

 In this we must consider, first, the formation of sexual 

 peculiarities in the males, and the secondary char- 

 acters by which they are aided in the courtship of the 

 females; and only secondly the reactions of these pe- 

 culiarities on the alteration and progress of the species in 

 general. 



The fundamental idea of Darwin's theory of selection 

 is ■ therefore, that the cumulative power of selection ex- 

 ercised by man in the breeding of races, is, in nature, 

 replaced by the struggle for life; and that in the course 

 of time, by the cumulation of advantages primarily 

 slight and becoming more and more prominent, lower 

 organisms are converted into higher ones. The process 

 is incessant. " It may be metaphorically said, that 

 natural selection is daily and hourly scrutinizing through- 

 out the world the slightest variations, rejecting those that 

 are bad, preserving and adding up all that are good; 

 silently and insensibly working, whenever and wherever 

 opportunity offers, at the improvement of each organic 

 being in relation to its organic and inorganic conditions 

 of life." ** 



The following chapters will introduce us more nearly 

 to this theory, its truth, possibility, application, and con- 



