CHAPTER VIII 



THE INHERITANCE OF ACQUIRED 

 CHARACTERS 



1. The Forgetting of the Original Structure 



As pointed out above, adaptive change of genes, as a rule, can be 

 regarded as "Dauermodifikation" or durable modification. Since the 

 gradual, reversible change of genes takes place gradually under the 

 influence of environmental factor, the return to the original structure 

 on the removal of the environmental factor, which induced the change, 

 should take place also gradually, with the result that the changed 

 character continues to exist for some periods of time after the removal 

 of the factor. 



Durable modification, however, is found mainly with unicellular 

 organisms. In the case of higher, multicellular organisms the modi- 

 fication is, as a rule, restricted to one generation, not being inherited 

 to progeny, although its transmission from soma to soma appears to 

 be possible. This is apparently not to be attributed to the failure of 

 the transmission of the change of the somatic cell to the germinal, 

 since, as will be discussed below, there are good reasons to consider 

 that the transmission is quite possible. The general non-inheritance 

 of acquired characters in higher organisms should be ascribed to the 

 fertilization in which the changed pattern of the germ cell is to re- 

 turn to its original state through the structural disturbance by the 

 germ cell of the other sex. This return to the original pattern is 

 nothing but the rejuvenation caused by the fertilization as already 

 stated. 



This is also the case with unicellular organisms. It has several 

 times been reported that the occurrence of conjugation or autogamy 

 was particularly likely to result in rapid reversal of an adaptive 

 change. In every case described the adaptive change can take place 

 only during periods of asexual reproduction, in cells originally derived 

 from single ancestral individual. 



For example, by culturing for long periods in the presence of 

 sublethal amounts of arsenious acid, a strain of Paramecium was 

 obtained which was several times as resistant as its parent (72). This 



