166 THE EVOLUTION OF LIVING BEINGS. 



If the presence- and absence-hypothesis holds good, 

 they may really be mutants, arisen by a loss of a gen 

 or factor, as a result of faulty inheritance e. g., 

 after our present conceptions, as a result of accidental 

 irregularities in karyokinesis, but even if this were the 

 case, such an occurence would not materially assist the 

 mutation theory because evolution by a process of re- 

 peated losses is inconceivable. 



The mutation theory requires proof of the existence 

 7 of progressive mutants e. g. proof that dominants can 

 arise from recessives. 



As we have seen, there is not a particle of proof for 

 such an occurence. It need hardly be added, that it is 

 not sufficient to prove the occurence of a dominant in a 

 bed of recessives, but that it is necessary to prove that 

 the dominant arose from a recessive. 



The mere presence of a dominant in a bed of reces- 

 sives, proves as little that it arose from a recessive as 

 the presence of a cuckoo's egg in the nest of a sparrow 

 proves that this egg arose from a sparrow's egg. 



Finis. 



73 35 



