SEXUAL SELECTION. I45 



of the organic morphological constituents, single parts 

 and organs may be modified and perfected in definite 

 advantageous directions, 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 strongest, 

 another very influential phenomenon comes into play 

 where the desire for propagation is concerned, which 

 Darwin has designated as " sexual selection," and elabo- 

 rated 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 

 characters by which they are aided in the courtship of 

 the females ; and only secondly the reactions of these 

 peculiarities 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 

 exercised 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 na- 

 tural 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- 



L 



