REPRODUCTION AND SEX 



463 



Tile-fish (Lopholatilus) for a long stretch of years after 1882, pro- 

 bably as the result of some oceanic cataclysm ; but slight fluctuations 

 are the rule. And even the Tile-fish has been reinstated. A sudden 

 increase may bring its own check in the growing scarcity of food; 

 a sudden decrease may relieve the intra-specific competition, so 

 that the mortality of young stages is reduced, and the number of 

 the population is re-established. 



In his famous Essay on Population (1798) Malthus showed that 

 the increase of human population tends to outrun the means of 

 subsistence, but is met by various "positive" checks (disease, 

 starvation, war, infanticide) and by various "prudential" checks 

 (ethical and economic restraint, which may imply some artificial 

 method of preventing conception). The teaching of Malthus was: 



Diagram indicating in six different types the inverse ratio of reproduction or 

 genesis (upper perpendiculars, 1-6) to individuation (lower perpendiculars, 

 1-6). 



To avoid the horrors of "positive" checks, put "prudential" checks 

 into operation. This is a large question by itself; we are here most 

 concerned with the fact that the essay of Malthus came as a powerful 

 suggestion to both Darwin and Wallace, who extended the induction 

 to plants and animals, recognising in their increase one of the funda- 

 mental conditions of the struggle for existence, and finding the 

 analogues of Malthus's "positive" checks in the various modes of 

 elimination that operate in Natural Selection. 



Not less important was Herbert Spencer's analysis of the laws 

 of multiplication. To these we shall return, but the gist of his thesis 

 must be stated here. Including under the term individuation all the 

 race-preserving processes by which the individual life is completed 

 and maintained, and under the term genesis all the processes that 

 lead to the production of new individuals, Spencer maintained that 



