292 OBITUARY X 



Considering the difficulties which surround the 

 question of the causes of variation, it is not to be 

 wondered at, that Darwin should have inclined, 

 sometimes, rather more to one and, sometimes, 

 rather more to another of the possible alternatives. 

 There is little difference between the last edition 

 of the " Origin " (1872) and the first on this head. 

 In 1876, however, he writes to Moritz Wagner, 

 " In my opinion, the greatest error which I have 

 committed has been not allowing sufficient weight 

 to the direct action of the environments, i.e., food, 

 climate, &c., independently of natural selection. 

 . . . . When I wrote the ' Origin/ and for some 

 years afterwards, I could find little good evidence 

 of the direct action of the environment ; now there 

 is a large body of evidence, and your case of the 

 Saturnia is one of the most remarkable of which 

 I have heard." (Ill,, p. 159.) But there is really 

 nothing to prevent the most tenacious adherent to 

 the theory of natural selection from taking any 

 view he pleases as to the importance of the direct 

 influence of conditions and the hereditary traiis- 

 missibility of the modifications which they produce. 

 In fact, there is a good deal to be said for the view 

 that the so-called direct influence of conditions is 

 itself a case of selection. Whether the hypothesis 

 of Pangenesis be accepted or rejected, it can hardly 

 be doubted that the struggle for existence goes on 

 not merely between distinct organisms, but between 

 the physiological units of which each organism is 



