348 THE SURVIVAL OP THE UNLIKE. [xXI 



organism and the male sex -elements from the destruc- 

 tive or dissociative (katabolic) changes. It is probable, 

 especially in organisms of increasing complexity, that 

 these opposed changes of the organic structure cannot 

 take place simultaneously, at least in equal degree; and 

 it therefore happens that even in the lowest hermaphro- 

 dite or bisexual organisms the sexes develop or ope- 

 rate alternately, the individual being at one time essen- 

 tially male and at another time essentially female. In 

 this way it first came, no doubt, that self-fertilization 

 was more or less prohibited. Now, as the struggle 

 for existence increased, every organism, whether animal 

 or plant, was obliged to dispense with every superfluous 

 ambition and to concentrate its powers upon those 

 organs and functions which were an absolute necessity 

 to the prolongation of the life of the species. There 

 came a tendency in certain individuals to eliminate 

 one sex and in other individuals to eliminate the other 

 sex ; so in time there came to be male and female, or 

 a division of labor. But other advantages besides a 

 mere division of labor resulted from this disjunctive 

 evolution. The male and female individuals became 

 unlike in other features than those of mere sex, and 

 the offspring of their union were more variable than 

 those which might spring from one parent, or which 

 had no father and mother. The more variable the 

 offspring of any species, the greater are the (chances 

 that many of them will find congenial or at least 

 tolerable places in nature, and the safer is the species 

 in the contest for life. It is the opinion of some 

 modern philosophers — Weismann and his followers — 

 that the chief use of sex is to originate variation in 

 the offspring. 



