LAWS OF MULTIPLICATION. 265 



But again, since fatness is associated with sterility, it is often argued that high 

 feeding is unfavorable to genesis. Obesity, however, is now known to be 

 associated with imperfect assimilation, with physiological impoverishment or 

 degeneration,— by no means with that constitutional wealth which is favorable 

 to fertility. If, in short, we bear in mind that truly high nutrition means only 

 due abundance of, and due proportion among, all the substances which the 

 organism requires, and that their perfect assimilation by the organism is also 

 needful, such objections to the ^generalization not only disappear, but such a 

 phenomenon' as the coincidence of returning fertility with disappearing obesity 

 affords a confirmatory argument. 



Organisms having aberrant modes of life are next appealed to for crucial 

 evidence bearing on these general doctrines. Thus, turning to vegetable and 

 animal parasites, which combine superabundant nutrition with greatly diminished 

 expenditure, the enormous fertility exhibited by all such forms is seen to be the 

 necessary correlative of such a state of nutrition and expenditure, and not 

 merely an acquired adaptation to their peculiar difficulties of survival. The 

 reversion exhibited by so many species (especially among the higher arthropods, 

 for example, Aphis, Cecidomyia) from sexual reproduction to primitive forms 

 of genesis, is explained by pointing out that such species are peculiarly situated 

 in obtaining abundant food with little exertion. Among bees, ants, and termites 

 alike, the enormous fertility of the inactive and highly nourished queen-mother 

 are obviously also cases in point. 



The inverse variation of genesis with individuation has now been demon- 

 strated inductively as well as deductively, and that for each element of the latter 

 (growth, development, or activity). Vet before discussing its application to the 

 problems of the multiplication of the human species, two points remain, — a 

 question has to be answered, and a qualification made. The question, only 

 partially answered in course of the preceding argument, is, How is the ratio 

 between individuation and genesis established in each special case ? and the 

 answer is. By natural selection. This may determine whether the quantity of 

 matter spared from individuation for genesis be divided into many small ova or 

 a few larger ones ; whether there shall be small broods at short intervals, or 

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

 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 antogonism above traced. 



The needed qualification arises on introducing the conception of evolutionary 

 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 individua- 

 tion 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 individuation and its genesis. And thus, though the 

 increment of individuation 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. 



