CONTROL OF HEREDITY: EUGENICS 397 



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 

 factors are comparable to the changes which 

 take place in certain atoms, for example ra- 

 dium, by which the element itself is changed in 

 an irreversible manner. The discoveries of 

 Mendel show us how to follow old characters 

 through many combinations and through many 

 generations, but they do not show us how new 

 characters arise. These discoveries have given 

 us an invaluable method of sorting and combin- 

 ing hereditary qualities, but Mendelian inheri- 

 tance as such does not furnish the materials for 

 evolution. 



