OUR NATURAL INHERITANCE 81 



Man work into one another's hands. When Nature 

 suppHes the raw material in the form of heritable varia- 

 tions and mutations, and Man supplies the sieve, whether 

 by bringing similar desirable forms together or by 

 eliminating undesirable variants whenever they show 

 face, great results may ensue. We see this in cereals 

 and potatoes, cattle and poultry, and in a score of other 

 cases. 



As we have already noticed in the first chapter, Men- 

 del put a clue — an Ariadne thread — into the hands of 

 breeders and cultivators. It is becoming increasingly 

 clear that Mendelism can enable a breeder or cultivator 

 to reach his desired end more surely, more rapidly, and 

 more economically. His new knowledge shows him 

 how desirable qualities of the unit-character type can 

 be grafted on to a stock, and how undesirable qualities 

 can be slipped of?. Desirable qualities are continually 

 welling forth from life's inexhaustible fountain of change. 

 Mendelism has shown the breeder and cultivator how 

 to utilise these more effectively. The greatest difficulty 

 is with ourselves. In the eighth chapter we shall briefly 

 discuss the question. What is practicable in the way of 

 human eugenics in the stricter sense — the improvement 

 of the human breed? 



