INTERMINGLING OF RACES 251 



One other matter to be kept in mind in this connection 

 is the impossibility of knowing what factors have survived 

 and what have perished. The great differences between 

 individuals in inherent traits both physical and mental, 

 make it probable that even within a race the average 

 capacity of some strains is greater than others. This 

 seems a fair deduction after making all due allowances 

 for changes in the spirit of the times which accelerate or 

 retard the development of natural ability. Now we do not 

 know and cannot know how the hereditary factors existent 

 to-day compare with those existent 2000 years ago. Selec- 

 tion within the population is an invariable concomitant of 

 human existence. There is a selective death rate, selec- 

 tive mating, selective fertility, each influenced by many 

 conditions. These selective agencies do not remain the 

 same, nor does the material upon which they work. We 

 do not know, for example, whether the most desirable 

 germ plasm of Greece, of Rome, of Mediaeval Europe, has 

 been passed on or has ceased to exist. The world has 

 received a great legacy in the creative production of the 

 master men of the past ; that it is their heir in physical 

 fact is not so certain. In the strictly biological sense, i.e., 

 in the material basis of heredity, the world may be better 

 or it may be worse than it was in the time of Pericles. 

 This phase of the subject is mentioned because one often 

 hears comments on the degeneracy of certain nations who 

 have had periods of enviable greatness. Social condi- 

 tions may be the cause, but it should not be forgotten 

 that they are not the sole possible cause. Essential 

 hereditary factors may have been cut off, may have been 

 wholly eliminated. 



These genetic ideas of race heredity among mankind 



