333 THE EVOLUTION THEORY 



upwards towards the forehead, the hind-limbs towards diminution, 

 the lungs towards lengthening, the tail towards broadening out. But 

 each of these variational tendencies was always only one of several 

 possibilities, and that the particular path which led towards the 

 ' goal ' was followed was due to the fact that the others plunged into 

 the abyss to which the wrong paths led, that is to say, they were 

 weeded out by selection. Thus germinal selection offers a possibility 

 of reconciliation between Nageli's and Darwin's interpretations, which 

 seem so directly contradictory ; for the former referred everything 

 to the hypothesis of an internal evolutionary force, the latter rejected 

 this, and regarded natural selection as the main, if not the exclusive 

 factor in evolution. The internal struggles for food, which we have 

 assumed as occurring in the germ-plasm, represent an internal force, 

 though not in the sense of Nageli, who thought of determining 

 influence operative from first to last, but still an impelling force, 

 which determines the direction of variation for the individual deter- 

 minants, and must therefore do the same for the whole evolution 

 up to a certain point ; for it is only the possible variations of the 

 determinants in a germ-plasm which can be chosen, selected, combined, 

 and increased by natural selection, and every germ-plasm cannot give 

 rise to all sorts of variations ; the determinants contained in it con- 

 dition what is possible and what is not, and this is an important 

 limitation to the efficacy of natural selection, and to a certain extent 

 also implies a guiding and determining power on the part of the 

 internal mainspring, to wit, germinal selection. 



The essential difference between Darwin's view of the trans- 

 formation of forms and my own lies in the fact that Darwin conceived 

 of natural selection as working only with variations which are not 

 only due to chance themselves, but the intensification of which also 

 depends in its turn solely upon natural selection, while, according 

 to my view, natural selection works with variational tendencies which 

 become intensified through internal causes, and are simply accumulated 

 by natural selection in an ever-growing majority of ids in a germ- 

 plasm through the selection of individuals. 



This affects our view of the establishment of a specific type 

 in so far that my intra-germinal variational tendencies are not 

 necessarily, and not always due to chance, though they are so in most 

 cases. If certain determinants are impelled to vary in a particular 

 direction through climatic or any other influences, as we have seen 

 to be the case, for instance, with the climatic varieties of many 

 Lepidoptera, then the corresponding determinants in all the individuals 

 must vary in the same direction, and thus all the individuals of the 



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