SEXUAL SELECTION. 145 
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- 
