HUMAN SELECTION. ic 3 



rate of increase of population caused by a delay in the average 

 period of marriage. For when the age of marriage is delayed the 

 time between successive generations is correspondingly length- 

 ened ; while a still further effect is produced by the fact that the 

 greater the average age of marriage the fewer generations are 

 alive at the same time, and it is the combined effect of these three 

 factors that determines the actual rate of increase of the popula- 

 tion.* 



But there is yet another factor tending to check the increase 

 of population that would come into play in a society such as we 

 have been considering. In a remarkable essay on the Theory of 

 Population, Herbert Spencer has shown, by an elaborate discus- 

 sion of the phenomena presented by the whole animal kingdom, 

 that the maintenance of the individual and the propagation of the 

 race vary inversely, those species and groups which have the 

 shortest and most uncertain lives producing the greatest number 

 of offspring ; in other words, individuation and reproduction are 

 antagonistic. But individuation depends almost entirely on the 

 development and specialization of the nervous system, through 

 which, not only are the several activities and co-ordinations of the 

 various organs carried on, but all advance in instinct, emotion, 

 and intellect is rendered possible. The actual rate of increase in 

 man has been determined by the necessities of the savage state, 

 in which, as in most animal species, it has usually been only just 

 sufficient to maintain a limited average population. But with 

 civilization the average duration of life increases, and the possible 

 increase of population under favorable conditions becomes very 

 great, because fertility is greater than is needed under the new 

 conditions. The advance in civilization as regards the preserva- 

 tion of life has in recent times become so rapid, and the increased 

 development of the nervous system has been limited to so small 

 a portion of the whole population, that no general diminution in 

 fertility has yet occurred. That the facts do, however, accord 

 with the theory is indicated by the common observation that 

 highly intellectual parents do not as a rule have large families, 

 while the most rapid increase occurs in those classes which are 

 engaged in the simpler kinds of manual labor. But in a state of 

 society in which all have their higher faculties fully cultivated 

 and fully exercised throughout life, a slight general diminution 

 of fertility would at once arise, and this diminution, added to 

 that caused by the later average period of marriage, would at 

 once bring the rate of increase of population within manageable 

 limits. The same general principle enables us to look forward to 



* See Inquiries into Iluman Faculty and its Development, p. 321 ; and Hereditary 

 Genius, p. 353. 



