Modification and Variation. 309 



How then is progress possible if none of the modifica- 

 tions which the body suffers is transmitted from parent to 

 offspring ? To this question the reply must be that though 

 modification is, on this view, excluded from taking any 

 direct share in race-progress, yet there is still variation. 

 Modifications are those changes which are in some way 

 wrought in the body structure ; and variations, those 

 differences which are of germinal origin. That variation 

 of germinal origin is a fact in organic nature is admitted 

 on all hands ; and that some variations are adaptive is 

 also unquestioned. Transmissionists contend that modifi- 

 cation in a particular direction in one generation is, 

 through transmission of the change in some, at present 

 unexplained, way from the bodily tissues to the germinal 

 cells, a source of similar variation in the next generation. 

 Selectionists, on the other hand, exclude this source of 

 variation, contending that the supposed evidence in its 

 favour is insufficient or unsatisfactory. But their whole 

 theory depends on the occurrence of variations, of which 

 those that are in unfavourable directions are weeded out, 

 while those that are useful and adaptive remain. How 

 these variations originate in the germ need not here be dis- 

 cussed. Let us assume that variations of germinal origin 

 in a great number of directions do as a matter of fact occur. 



This then is how the matter stands. All acknowledge 

 the existence of variations, and admit that their proximate 

 source is in the fertilized ovum. All admit that the 

 individual is through its innate plasticity in greater or 

 less degree capable of adaptive modification. Trans- 

 missionists contend that the effects of modification are 

 somehow transferred to the germinal substance, there to 

 give origin to variations. Selectionists deny this trans- 

 mission, and contend that adaptive variations are inde- 

 pendent of adaptive modifications. 



