290 



THE EVOLUTION OF SEX. 



effected upon the conception of Alalthus"^ by Darwin, will the 

 utility of such increasing elaboration be disputed. Thus the 

 full inductive verification of Spencer's law involves a detailed 



Author. 



Development of Theory of Population. 



Practical 



Action 

 Deduced. 



I. 



Non- bio- 

 logical 

 writers 

 (prede- 

 cessors 

 and op- 

 ponents 

 of Mal- 

 thus). 



Increase of population 

 does not tend to out- 

 run subsistence. 









II. 



Malthus. 

 1798. 



Increase of population But meets checks : 

 tends to outrun that A. Positive, 

 of subsistence. B. Preventive. 





To avoid A, 

 adopt B. 



III. 



Dar\vin. 



1859. 



Do. 



Hence _ struggle 

 for existence : 



A. Natural 

 selection. 



B. Artificial 

 selection. 



Leading to 

 evolution. 



Laissez -/aire, 

 i.e., on ac- 

 count of ad- 

 vantage to 

 species from 

 A, avoid B. 



IV. 



Spencer. 

 1852-66. 



Do. 

 Rate of multiplication 

 investigated _ for dif- 

 ferent species, and 

 shown tovarj- inverse- 

 ly as individuation. 



Do. 



Do. 

 Also lead- 

 ing to 

 e v 1 u- 

 tion _ of 

 species. 



Do. 

 \Individiiate. ] 



comparison of the rates of reproduction of each group of 

 organic species, with their observed degree of individuation 

 (first in each of its factors, and finally in their sum), devia- 

 tions from the inverted symmetry of the theoretic curves 

 (see fig. opposite) having to be separately discussed. Natural 

 selection also requires a yet deeper analysis; the limits and 

 possibilities of artificial selection are but little known, while 



* It is also interesting to compare Malthus's view of population, tend- 

 ing to increase in geometrical proportion and substance only in arithmetical, 

 with Spencer's demonstration of the limit of growth already simimarised 

 (see p. 220), the more so when we bear in mind that reproduction is dis- 

 continuous growth. The precise statement of Malthus becomes confirmed, 

 as regards the cell, if not the cell aggregate. 



