CHAPTER XXI. 

 DIPLOID ORGANISMS AND MUTATION. 



We have given our reasons for being sceptical as to 

 the existence of mutations. 



This scepsis is partly based on fact, partly on cir- 

 cumstantial evidence. The fact is, that we possess no 

 means to establish complete specific purity experimen- 

 tally, and consequently are never sure of the purity of 

 our material. 



Certainty of purity however is a conditio sine qua non 

 to obtain proof of the existence of mutation in living 

 beings, just as chemical purity is a conditio sine qua non 

 to obtain proof of the existence of mutability of the ele- 

 ments. 



The circumstantial evidence is, that all so called mu- 

 tants are recessives e. g. arise in material in which 

 impure individuals are indistinctible at sight from 

 pure ones, which makes it very probable that the aber- 

 rant individuals were no mutants at all, but segregates 

 from heterozygotes, indistinctible from the pure do- 

 minants. 



Circumstantial evidence always contains an element 

 of uncertainty and the evidence from the recessives is 

 no exception to the rule. 



The fact that the ,,mutants" are always recessives is 

 namely no proof that they are segregates. 



