VARIATIONS AND MODIFICATIONS ii 



sets of facts, both expressions of the hereditary relation, — 

 inertia, persistence, continuity, resemblances, on the one hand ; 

 deviation, novelty, differences, on the other. 



Can we hope to discriminate an apparent difference between 

 parent and offspring, which is really due to an incompleteness 

 in the expression of the inheritance, from a real difference, which 

 is due to the dropping out of an old hereditary item or the 

 addition of a new one ? Can we distinguish between inborn 

 peculiarities — germinal variations — and acquired, nurtural pecu- 

 liarities ? Can we distinguish between variations which seem 

 to be simply a little less or a little more of some hereditary 

 character, and variations which involve something new ? 

 These and similar questions must be faced in the study of 

 variation. 



Modifications. — Furthermore, whenever the study of the facts 

 of inheritance becomes critical, it is necessary to try to dis- 

 criminate between inborn changes, which must have a germinal 

 origin, and are therefore in the strict sense inherited, and are 

 liable to be transmitted, and those theoretically quite different 

 changes which are acquired by the body of the individual off- 

 spring as the result of peculiarities in function and environment. 

 This is the contrast between germinal variations and bodily 

 modifications, a contrast which is of fundamental importance 

 in several ways. It is important to try to distinguish resem- 

 blances and differences due to inherited nature from resemblances 

 and differences due to nurture. A collier may have his collier 

 father's red hair, and he may also resemble him in having " col- 

 lier's lung." But while the first resemblance is a fact of in- 

 heritance, the second is due to the similarity in their life-con- 

 ditions. This distinction remains important whatever conclusion 

 be reached in regard to the transmissibility of modifications, 

 but its importance is enhanced when we discover that practically 

 all variations (except sterility) are transmissible, though not 

 always transmitted, and that the evidence of any modification 



