522 STUDIES, SCIENTIFIC AND SOCIAL chap. 



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 Fopidation Herbert Spencer has 

 shown, by an elaborate discussion of the phenomena pre- 

 sented 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 short- 

 est and most uncertain lives producing the greatest num- 

 ber of offspring ; in other words, individuation and repro- 

 duction 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 popu- 

 lation. But with civilization the average duration of life 

 increases, and the possible increase of population under 

 favourable conditions becomes very great, because fertility 

 is greater than is needed under the new conditions. The 

 advance in civilization as regards the preservation 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 com- 

 mon 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 labour. But in a state of society in which 

 all will 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 that distant future when the 

 world will be fully peopled, in perfect confidence that an 



