652 Studies in the Theory of Descent. 



rarely happened in former epochs of the earth's 

 history. Even climatic changes, which we might 

 at first regard as of this character, and which pro- 

 duce a modification in one fixed direction, occur 

 always so gradually that the species has time 

 either to adapt itself to the conditions in this or 

 that direction, according to the variations possible 

 to its physical nature, or else to emigrate. 



It thus appears to me erroneous to suppose 

 that variability must be " merely undetermined " 

 in order to complete its part in Darwin's theory of 

 selection, and its "illimitedness" seems tome also 

 as little necessary for this purpose. Von Hart- 

 mann imagines that it is only unlimited variability 

 that furnishes a guarantee that any type, to what- 

 ever extent diverging from its point of departure, 

 will be reached by the Darwinian method of 

 gradual transmutation by means of selection and 

 the struggle for existence. 



But who has ever asserted that any type can 

 be reached from any point ? Or if anybody has 

 said such nonsense, who can prove that its ad- 

 mission is necessary for the theory of selection ? 

 Nowhere in systemy do we see any point of 

 support for such an assumption. But when Von 

 Hartmann imagines that the " unlimited " varia- 

 bility \7hich he postulates for Darwin " is in itself 

 unlimited, the limits of its divergence in a given 

 direction being found, not in itself, but only in 

 external obstacles," he conceives variability to be 



