354 Professor J. Arthur Thomson [March 80, 



breed. But (3) the hybrid may also be very different from either 

 parent, showing features which appear to be quite novel, or which on 

 close investigation are seen to be interpretable as the reassertion of 

 the characters of a remoter ancestor. In short, it may show either a 

 new variation or a reversiou. The extraordinary fact is that at least 

 two of these different results may be illustrated in one brood or litter 

 of hybrids. 



The facts above referred to may be considered in another aspect, 

 in terms of what is called the quality of prepotency, with which 

 breeders have been for a long time familiar. The term refers to the 

 fact that in the development of a character the paternal or the 

 maternal qualities may predominate, as in unequal blending where 

 there is relative prepotency, or in exclusive inheritance where the 

 prepotency in respect to a given character is absolute. It seems 

 doubtful whether we gain much by using the word, since all these 

 general terms are apt to form the dust particles of intellectual fog, 

 but what we have to do with is the fact that in respect to certain 

 characters the paternal inheritance seems more potent than the 

 maternal, or vice versa. Thus in man the father is usually prejjotent 

 in the matter of stature, and breeders give many instances where 

 certain, even trivial, characters of sire or dam reappear persistently 

 in the offspring irrespective of the nature of the other parent. 



It seems that one of the ways in which the quality of pre- 

 potency may be developed is by inbreeding, as Prof. Ewart and 

 others have maintained. " Some breeders say that they can produce 

 a horse so prepotent, so fixed by interbreeding (inbreeding) that it 

 will produce its like however mated " ; and there is much evidence 

 to show that, of two parents, the more inbred — up to a certain limit 

 of stability — is likely to have the greater influence on the offspring. 



As inbreeding may be frequent in nature, especially among 

 gregarious and isolated groups, and as it tends to develop prepotency, 

 we are able to understand better how new variations may have been 

 fixed in the course of evolution. And we can better understand the 

 position maintained by Reibmayr, that the evolution of a human race 

 implies alternating periods of dominant inbreeding, and dominant 

 cross-breeding. The inbreeding gives fixity to character, the cross- 

 breeding averts degeneracy and stimulates new variations which form 

 the raw material of progress. The Jews, especially in isolated 

 colonies, may serve to illustrate persistent inbreeding, which we may 

 contrast with the complex cross-breeding at present conspicuous in 

 America. 



Until we have more precise statistical data in regard to blended, 

 exclusive, and particulate inheritance, we cannot hope to simplify the 

 matter with any security. But perhaps a unified view will be found 

 in the theoretical conception of a germinal struggle in the arcana of 

 the fertilised ovum — a struggle in which the maternal and paternal 

 contributions may blend and harmonise, or may neutralise one 

 another, or in which one may conquer the other, or in which both 



