288 THE EVOLUTION OF SEX. 



or larger broods at longer intervals ; or whether there shall be many unpro- 

 tected offspring, or a few carefully protected by the parent. Again, survival 

 of the fittest has a share in determining the proportion of matter subtracted 

 from individuation for genesis. Yet this operation of natural selection goes 

 on strictly under the limits of the antagonism above traced. 



The needed qualification arises on introducing the conception of evolu- 

 tionary change. If time be left out of account as hitherto, — or, what is the 

 same thing, if all the species be viewed as permanent, — the inverse ratio 

 between individuation and genesis holds absolutely. But each advance in 

 individual evolution (it matters not whether in bulk, in structure, or in 

 activities) implies an economy ; the advantage must exceed the cost, else it 

 would not be perpetuated. The animal thus becomes physiologically 

 richer ; it has an augmentation of total wealth to share between its in- 

 dividuation and its genesis. And thus, though the increment of individua- 

 tion tends to produce a corresponding decrement of genesis, this latter will 

 be somewhat less than accurately proportionate. The product of the two 

 factors is greater than before ; the forces preservative of race become 

 greater than the forces destructive of race, and the species spreads. In 

 short, genesis decreases as individuation increases, yet not quite so fast. 



Hence every type that is best adapted to its conditions — every higher 

 type — has a rate of multiplication that ensures a tendency to predominate. 

 For though the more evolved organism is the less fertile absolutely, it is 

 the more fertile relatively. 



The whole generalisation admits of the simplest graphic 

 illustration. For if the line AB represents the aggregate 



C 



A ! B 



matter or energies, the structures or the functions, of the 

 organism, of which AC denotes the amount devoted to in- 

 dividuation and CB to reproduction, the inverse variation of 

 AC to CB is obvious, as also if AC and CB represent the 

 psychological obverse of these two classes of function. Nor 

 does an increase in total energy modify this, as when the 

 stronger members of a species frequently also exhibit greater 

 reproductive power; for if in one case AB = 2o, of which 

 C13 = 4, and in another AB = 25, CB may become 5 without 

 any rise of reproductive ratio, since 0^7 = WV- ^^ut if the species 

 be evolving, the advance in individuation implies a certain 

 economy, of which a share may go to diminish the decrement 

 to genesis, as above explained. 



i^ 4. Spencer'' s Application of his Results to Man. — In ex- 

 tending this hard-won generalisation to the case of man, the 

 concomitance of all but highest total individuation with all but 

 lowest rate of multiplication (the enormous bulk of the elephant 

 involving a yet greater deduction from genesis) is at once 

 apparent. Comparing different races or nations, or even 



