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 

 A 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 

 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. 



