54 THE CONTROL OF LIFE 



architectural style or plan is the same in all. Some of 

 the minor features which are crisply defined behave in 

 a remarkable way in inheritance, refusing to blend with 

 corresponding but contrasted characters. They are 

 continuous from one generation to another, appearing 

 in more or less intact expression in a certain proportion 

 of the offspring, and being quite absent from others. 

 They behave like entities, as if (in typical cases) they 

 could neither be split up nor blended. They have been 

 compared to chemical radicles {e.g. NH4) which can 

 enter into many different associations, but behave as 

 unities. Such characters are called * unit-characters ' 

 or Mendelian characters. Recent work has shown that 

 many of our more superficial characters are of this 

 nature. We are in some measure composed of strands 

 of ' unit-characters,' a familiar instance being the colour 

 of the eye. It is possible that the stable fundamental 

 block of the inheritance (the specific hereditary organisa- 

 tion) is made up of a very large number of coherent 

 unit-characters firmly linked together. To some 

 students of heredity it seems rather as if the stable 

 foundation block were made up of a blend of ancestral 

 contributions. In either case, the result of ages upon 

 ages of sifting has been that there is now little or no alter- 

 native as regards the general human features. It is 

 therefore probable that the variations, e.g. in the human 

 brain, that the future may have in store for mankind 

 must be congruent with the general style of brain 

 architecture which has, as it were, come to stay forever. 

 There is a growing body of evidence that some of 



