GENETICS 259 



of domesticated animals and plants that are of economic value. These 

 results have been more simple and clear in the case of plants than in that 

 of animals, though the end products have been scarcely more valuable. 

 Inheritance in animals is very complex in nearly all characteristics which 

 are of commercial worth, and the practice of the breeder is still very 

 largely the method of cut and try. But even by this empirical method 

 the milk-production of cattle, the egg-laying qualities of poultry, the wool- 

 clip of sheep, the productivity of the silk-worm and many other economic 

 features of animals have been marvelously improved. In plants the 

 economically important features are more often inherited in simple 

 fashion, and it is possible to apply promptly the principles of heredity 

 which have been elaborated since 1900. By these means the produc- 

 tivity of wheat and other grains, and of hay, has been appreciably in- 

 creased. It has been possible to combine in one variety of wheat, for 

 example, such desirable qualities as high yield, stiff straw, winter hardi- 

 ness, and resistance to rust; in oats, high yield with the absence of hulls; 

 in tobacco, high number and desirable shape of leaves with proper 

 texture and "grain. " And the end is not yet. The prospects for further 

 valuable improvements are bright. 



In human beings the application of the knowledge of heredity has 

 scarcely begun. Progress has been slow for the reason that such applica- 

 tion must either be voluntary, which requires much education of the 

 public, or must be enforced by legislation, which always meets with 

 objections from those to whom "personal liberty " is dear. Furthermore, 

 less is definitely known of heredity in man than in domestic animals, 

 because knowledge can only come from family histories, not experiments, 

 and family records can seldom be traced for many generations. While 

 much that is known could well be applied voluntarily by intelligent 

 people, legislation should limit itself for the present to those characters 

 which are of the greatest social importance and whose heredity is best 

 known. Feeble-mindedness is such a characteristic, and radical steps 

 looking toward its eradication would be justified even in the present 

 state of knowledge. 



References 



Babcock, E. B., and R. E. Clausen. Genetics in Relation to Agriculture. 



Bateson,,W. Mendel's Principles of Heredity. 



Castle, W. E. Genetics and Eugenics. 



CoNKLiN, E. G. Heredity and Environment in the Development of Men. 



Morgan, T. H. Heredity and Sex. 



Morgan, T. H. The Physical Basis of Heredity. 



Morgan, T. H., A. H. Sturtevant, H. J. Muller and C. B. Bridges. The 



Mechanism of Mendelian Heredity. 

 Punnett, R. C. Mendelism. 



