THE PURPOSIVE IMPROVEMENT OF THE HUMAN RACE 567 



turn the current of human evolution from degeneracy to 

 progress. Already we know^ how to improve the breeds of 

 domestic animals and cultivated plants; we know that man 

 also is a hving creature and that all the principles of heredity 

 and development, of progress or degeneration, of hfe or 

 death apply to man as well as to the humblest animal or 

 plant. Mankind could, if it would, breed a healthier, more 

 intelHgent, more ethical type than the general average of the 

 existing race. Exactly the same principles which are used 

 so successfully in the improvement of horses or cattle or 

 crops would produce corresponding results if apphed to 

 human reproduction and development. 



PRINCIPLES OF GOOD BREEDING 



What are these principles of good breeding which have 

 doubled the best speed of horses, the best weight of cattle, 

 the best yield of wheat during the past century? They 

 may be summed up under two general heads: (i) improved 

 heredity through selective breeding: (2) improved environ- 

 ment through better food, nurture, training. No successful 

 breeder neglects either of these factors. 



The only Hving bond between one generation and the 

 next is found in the germ cells, and whatever is inherited must 

 be carried in these cells. Of course no adult characters are 

 present in germ cells, but certain genes or inheritance factors 

 are contained in those cells and by the interaction of these 

 factors on one another and by their reactions to environmental 

 stimuli the adult characters gradually develop. Every 

 developed character is the result of many factors or causes, 

 some of which are inherited (that is they are present in the 

 germ cells) and others are environmental. For example, there 

 are multitudes of factors both hereditary and environmental 

 involved in the development of the eye; most of these are 

 common to all eyes and hence are non-differential, but as 

 between a blue eye and a brown one there must be at least 

 one differential factor and if this factor is located in the germ 

 plasm, as it is, the eye color is said to be inherited in spite 

 of the fact that many of the factors in the production of 

 this character are environmental. However, if the differential 



