460 



THE AM ERIC AX NATURALIST 



[Vol. L 



from one another by, probably, one electron lost from 

 each successive stage of the series. The series is thus 

 shown graphically by Sieveking (1913) : 

 ^RaC 2 



Ra->Em-^ Ra^ -> Ra# -> Ra(7 x -> RaZ) -> Ra# -> RaF 



III. Certain Consequences of the Theory 



1. The acceptance of this theory requires a special 

 explanation to account for adaptation. Eimer's theory 

 of orthogenesis posited the direct action of environment 

 on the germ plasm, a view which wider knowledge of 

 facts does not support. It follows naturally from the 

 hypothesis that new traits bear, at first, no relation to 

 environment any more than the polonium that is derived 

 from the uranium does. Darwin recognized that varia- 

 tions were not necessarily adaptive in their origin ; also 

 that it was not necessary that they should be adaptive in 

 order to survive. Darwin says : 4 



We clearly see that the nature of the conditions is of subordinate im- 



each particular form of variation. 



How then is adaptation brought about? Strictly, we 

 may say adaptation is not the thing that is brought about, 

 but rather absence of non-adaptiveness. Such adjust- 

 ment as we find is, doubtless, only such a residuum of 

 variants as has not proved incompatible with conditions 

 of existence. Two kinds of variations may survive: 

 (a) Those not incompatible with the conditions of the 

 present environment and (b) those which, while incom- 

 patible with present environment, are not incompatible 

 with some other environment into which the species may 

 migrate. 



2. Relation to the Role of Selection in Evolution.— 

 There is going on to-day a great discussion as to the 

 importance of selection in evolution. How does the 

 matter look from the standpoint of this theory. 



First, all are agreed that nothing has importance for 



* "Origin of Species," p. 9. 



