THE EVOLUTION OF SEX 43 



our Evolution in the present series) is that the 

 difference between the sexes expresses the 

 same kind of constitutional alternative that 

 we see in the contrasts between spermatozoon 

 and ovum, between animals and plants, 

 between active Infusorians and sluggish Sporo- 

 zoa, in fact between the free and the sedentary 

 groups which recur at so many levels of the 

 animal kingdom, and in short between pre- 

 ponderant activity and passivity in all forms 

 of life. 



The first step, at least, in the scientific 

 explanation of a phenomenon is to show that 

 it is a particular case of a general sequence, 

 and our theory of sex interprets the difference 

 between male and female as an instance of a 

 primeval and ever recurrent alternative in 

 variation namely, between increased ex- 

 penditure and increased income ; between 

 relative predominance of disruptive, analytic, 

 down-breaking processes, on the one hand, 

 and a relative predominance of constructive, 

 synthetic, up-building processes, on the other 

 hand; between, to put it shortly, a relative 

 preponderance, to the extent of constitutional 

 bias, of one or other of these katabolic and 

 anabolic processes which all physiologists 

 agree are mingled in the life of protoplasm 

 and cell, tissue and organ. The resulting bias 

 of this whole life-process, this ever-mingled 

 metabolism, is thus for us expressed in sex 

 and its subvarieties (themselves, as almost 

 every family shows, preponderatingly accented 

 one way or other), but also in the contrasts 

 of allied species and genera, of families and 

 classes, sub-kingdoms and kingdoms. Sex 



