326 THE TREND OF THE RACE 



industries which greatly affect the differential death rate of 

 relatively large numbers of the population; (3) the growth of 

 cities with the resulting subjection of their inhabitants to a 

 changed and often deleterious environment and mode of life; 

 (4) the effect of economic factors on the marriage and birth rates 

 of different stocks; and (5) the possible influence of altered 

 environmental factors on the trend of germinal variability. 



We shall consider briefly these different topics, although 

 it should be borne in mind that they are closely interrelated. 

 The striking increase of the populations of civilized countries 

 during the igth century is in large part due to the application of 

 science to industry which has increased enormously the wealth 

 with which nature has been compelled to reward the labors of 

 man. To a large extent also this increase of population has 

 resulted from the reduction of the death rate which has followed 

 the advances made in medicine, surgery, and especially those 

 branches of hygiene which are concerned with the control of 

 infections and epidemics. But whatever progress is made in the 

 art of saving life, the population of a country must obviously be 

 limited by the resources furnished by nature for human subsist- 

 ence. The yield of nature has been greatly increased by the 

 application of scientific discovery. Improvements in mining, 

 manufacturing, agriculture and transportation make it possible 

 for the earth to support a greatly increased number of inhabi- 

 tants, and human population even now comes sufficiently'near 

 obeying the law of Malthus to respond to the opportunities thus 

 created for its maintenance. 



Through the increase of numbers which industrial development 

 has made possible those races and peoples among whom such 

 development has reached a higher stage are enabled, by war or 

 otherwise, to prevail over races and peoples on a lower industrial 

 level. The Anglo-Saxon has doubtless been aided in extending 

 his domain on account of the very rapid growth of the population 

 of Great Britain which followed upon the unprecedented develop- 

 ment of her industries. The great economic development of 

 Germany, by creating opportunities for her people at home and 



