134 HEREDITY AND SOCIETY 



The thoroughbred horse has arisen by the union in 

 the past of Arab stallions with good English mares, 

 and the careful preservation of their progeny from 

 other strains of blood for many generations. The 

 nations of ancient Greece and Rome and modern 

 England and Japan arose from definite crosses at one 

 period or a few periods in time, and subsequent 

 isolation for longer or shorter periods of years, secured 

 to them by their geographical position on peninsulas 

 or islands. 



It is not easy to predict what elements will give a 

 successful cross. Firstly, it is clear that the parent races 

 themselves must be virile and sound. Secondly, if they 

 are too divergent, we get a mongrel race with the best 

 qualities of both ancestors blurred. The cross-breeds 

 of South America nowadays, and the mixture of races 

 which followed the expansion of Rome and heralded 

 its decay, point the dangers. Thirdly, the new race 

 must have a time of isolation and inbreeding to estab- 

 lish itself, show its worth and fix its characters ; and 

 this is the r61e played by the separation and political 

 crystallization of distinct nationalities. Fourthly, the 

 main theme of this book, a constant selection of the 

 best elements must be maintained within the nation. 

 Fifthly, occasional re-crossing with other, not too dis- 

 similar, strains may add to the vigour of the race, 

 provided once more that re-crossing be limited in time, 

 and that the new stock be appropriate and well-bred. 



Little attention has been given yet to the effect on 

 the average national character which is likely to be 

 produced by the continued immigration into England 

 of large masses of people from Eastern Europe. 



