DISTRIBUTION OF INHERITABLE TRAITS 185 



the Malays /'consanguinity, even the remotest, constitutes 

 an important obstacle to marriage." We read of the Is- 

 landers making voyages to other islands and carrying off 

 maidens for wives. In India and China marriage of persons 

 within the patronymic is against social ideals.^ European 

 ideals are largely a legacy of Roman law. Here the purely 

 formal and legal relations constituted as much of an obstacle 

 as blood relationship. A stepchild should not marry his 

 mother nor a father-in-law his daughter-in-law. Only re- 

 cently has a relic of these legal and non-biological interdic- 

 tions been removed in England by the repeal of the law pro- 

 hibiting a man from marrying his deceased wife's sister. 



Such wide-spread social barriers to close intermarriage, 

 even among the children of nature — one might almost say 

 especially among them — vindicates if not an instinctive re- 

 pugnance to, at least an apprehensiveness toward, such 

 marriages. We have still to inquire if there is any biological 

 basis for such apprehensiveness. The answer to this ques- 

 tion has been furnished in many places in the earlier part of 

 the book. Defects in the germ plasm tend to reveal them- 

 selves in the offspring of cousin marriages but tend to dis- 

 appear entirely in the children that are derived from out- 

 matings. On the other hand, undesirable positive traits 

 that are absent from both parents will not reappear in the 

 offspring even though the parents be cousins. One can easily 

 imagine a strain without any important defect, so that a 

 consanguineous marriage would, for generations, be unin- 

 jurious to the offspring; but such strains are doubtless rare. 

 We are told that in the family of the Ptolemies and in the 

 royal family of the Incas the marriage of brother and sister 

 repeatedly occurred but, as a friend of mine says, ''Where 

 are the Ptolemies and Incas now?'' The conclusion seems 



1 The foregoing summary of marriage limitations is based chiefly upon the 

 compiled data of Ploss-Bartels : Das Weib. 



