402 



LAWS OF MULTII'LICATION. 



having but small self-preservative powers are rapidly de- 

 stroyed, to be at the same time without reproductive powers 

 proportionately great. The defect of fertility, if extreme, 

 will result in the death of one generation before another has 

 grown up. If less extreme, it will entail a scarcity such 

 that in the next generation sexual congress will be too infre- 

 quent to maintain even the small number that remains ; and 

 the race will dwindle with increasing rapidity. If still less 

 extreme, the consequent degree of rareness, while not so 

 great as to prevent an adequate number of proereative 

 unions, will be so great as to render special food very abundant 

 and special enemies very few — will thus diminish the destruc- 

 tive forces BO much that the self-preservative forces will be- 

 come relatively great : so great, relatively, that when com- 

 bined with the small ability to propagate the species, they 

 will suffice to balance the small destructive forces. Suppose, 

 next, a species whose individuals have great powers of 

 self-preservation, while they have powers of multiplication 

 much beyond what is needful. The excess of fertilitj', if 

 extreme, will cause sudden extinction of the species by 

 starvation. If less extreme, it must produce a permanent 

 increase in the number of the species ; and this, followed 

 bv intenser competition for food and augmented number 

 of enemies, will involve such an increase of the dangers 

 to individual life, that the great self-preserving powers of 

 the individuals will not be more than sufficient to cope with 

 them. That is to say, if the fertility is relatively too great, 

 then the ability to maintain individual life inevitably becomes 

 smaller, relatively to the requirements ; and the inverse pro- 

 portion is thus established. 



So that when, from comparing the different states of the 

 same species, we go on to compare the states of different species, 

 we see that there is an analogous adjustment — analogous 

 in the sense that great mortality is associated with great 

 multiplication, and small mortality with small multiplication. 

 And we see that the unlikeness of the cases consists merely 



