REPRODUCTION AND SEX 487 



Contrariwise, although there may not be any marked dimorphism, 

 there may be a profound functional difference. There are many 

 facts, long since outlined in our Evolution oj Sex (1889), which go 

 to show that in their metabolism the male and the female are very 

 different. They run at different physiological rates; the metabolism 

 of the male is relatively more intense. The ratio of katabolism to 

 anabolism is greater in the male than in the female. We may quote 

 a few sentences from another biologist who takes the same view. 

 In his Sex Antagonism (1913) Mr. Walter Heape writes: "The Male 

 and the Female individual may be compared in various ways with 

 the spermatozoon and ovum. The Male is active and roaming, he 

 hunts for his partner and is an expender of energy; the Female is 

 passive, sedentary, one who waits for her partner and is a conserver 

 of energy." 



Perhaps the average differences between the sexes may be summed 

 up tentatively in this tabular contrast : 



Male. Female. 



Sperm-producer Egg-producer 



With less expensive reproduction With much more expensive repro- 

 duction 



More intense metabolism Less intense metabolism 



Relatively more katabolic Relatively more anabolic 



Often with shorter life Often with longer life 



Often smaller Often larger 



Often more brilliantly coloured Often quieter in colour and plainer 



and more decorative in decoration 



Rising to more intense outbursts Capable of more patient endurance 



of energy 



More impetuous and experimental More persistent and conservative 



More divergent from the youthful Nearer the youthful type 



type 



Often more variable Often less variable 



Making more of sex-gratification Making more of the family 



THEORIES OF SEX-DIMORPHISM 



Darwin's Theory. — As everyone knows, Darwin argued that 

 the evolution of dimorphic sex-characters might be accounted for 

 in terms of selection — especially Sexual Selection. This has two 

 modes: the combats between rival males and the preferential 

 mating where the female chooses or seems to choose. We shall 

 re discuss this theory in c(jnnection with evolution, and so here 

 simply indicate at present that there are some serious difficulties 

 in its way. (a) What is known experimentally in regard to selective 

 breeding, e.g. Johannsen's work, does not favour the view that the 



