152 DARWINISM TO-DAY. 



of time plays an important role in inheritance (heredity). 

 Schubeler found in his studies of the translation of the 

 northern boundary of the grain culture that the characters 

 newly acquired (heavier and earlier ripening seeds) per- 

 sisted for several generations when the forms were replanted 

 in the original [more southerly] habitat. De Vries in six 

 years selected corn which had an average of 20 rows of 

 kernels instead of the original 12 to 14, and held the plants 

 at this height of production through five years. When he 

 then planted seed from a i6-rowed ear, the average of the 

 ears gathered from this planting was in the first generation 

 still at 20 rows, and sank only in the next two years again 

 to 14 to 16. If he had continued his selection longer he 

 would have arrived at a more nearly constant form. De 

 Vries himself says : 'When the selection ceases, the selected 

 characteristics drop away and in practically the same length 

 of time which was necessary for the production of the new 

 race, that is within a few generations.' From this it follows 

 that a domestic race produced by slow persistent selection 

 through many thousands of generations would show the 

 same relative constancy or fixity as natural species, the 

 majority of which also must have originated slowly, for 

 otherwise the appearance of new species would be often 

 observed. If one wishes to be very conservative in this 

 matter one may declare : in the light of our present knowl- 

 edge we cannot say that artificial selection gives us any safe 

 means of judging just what degree of constancy [fixity] can 

 be attained by its means ; but it is not fair to say that be- 

 cause up to the present only a partial constancy has been 

 reached through artificial selection, natural selection cannot 

 have led to the production of constant species. All culti- 

 vated races have been relatively quickly, some indeed very 

 quickly, selected * and, therefore, they strike back very 

 quickly. This, however, need not be assumed for the slowly 

 arisen products of natural selection." 



