CONTROL OF HEREDITY: EUGENICS 387 



this method of hybridization or "heterozygo- 

 sis," as it has been called, offers an extremely 

 important means of quickly producing very 

 vigorous and fruitful individuals, but not lines 

 or races which breed true. 



This is what is meant by the control of he- 

 redity, namely the possibility of preventing 

 the reproduction of individuals with bad traits, 

 and of making new and favorable combina- 

 tions of old traits by means of selective 

 breeding, and of seizing upon and perpetuat- 

 ing new and favorable mutations. 



2. Origin of Mutations. — Mendelian asso- 

 ciation and dissociation of characters produces 

 new forms of adult animals and plants but not 

 new hereditary characters. Permutations of 

 Mendelian characters we may have almost 

 without number, of new combinations of these 

 there may be no end, but no new unit charac- 

 ters are formed by such temporary combina- 

 tions, no new inheritance factors are created or 

 evolved. New combinations of factors may 

 be compared to new combinations of chemical 

 elements; you can always get out of the 

 combination what went into it, whereas new 



