THE MARRIAGE OF KIN 



No Adequate Evidence That Any Evil Results from Consanguineous Matings, 



as Such, Although Where Both Stocks Are Weak the Offspring 



May Show Double Amount of Weakness. 



Edward Nettleship^ 

 University of London, England 



THE subject of marriage between 

 blood-relations should, I think, 

 engage the attention of all 

 who are interested in problems 

 bearing upon the improvement of the 

 race; it is at any rate one upon which 

 there has been, and perhaps still is, 

 much diversity of opinion. Such dif- 

 ferences of view are doubtless often 

 based, on the one hand, upon the 

 experiences of certain single families 

 where serious defects or degeneracies 

 have appeared in the offspring of con- 

 sanguineous marriages, and on the 

 other upon acquaintance with families 

 in which nothing undesirable has fol- 

 lowed the marraige of first cousins. 

 Indeed those who object, from what we 

 may call individual or single-family 

 experience, would perhaps be surprised 

 to find that the children of cousins 

 sometimes showed a decided improve- 

 ment upon their parents. In short I 

 venture to think that the subject is one 

 upon which we may well seek more 

 knowledge and greater clearness of 

 thought. 



The fundamental questions are (1) 

 whether the offspring of consanguineous 

 parents display inferior or degenerate 

 characters in larger proportion than do 

 the offspring of unrelated parents? 

 And (2), if such an effect can be shown, 

 is the appearance of these undesirable 

 characters attributable to something 

 produced de novo by the union of 

 parents related in blood, but who them- 

 selves contain no trace of such char- 

 acters, either manifest or hidden"" Or 

 are the defects only a result of both 

 parents being tainted, but not tainted 

 badly enough to show ? 



The second question is not merely 

 academic. For if consanguinity can 

 produce something bad, good, or in- 

 different that had never occurred before 

 in the genealogy then no cousin marriage 

 is safe. But if it is only a case of in- 

 heritance from both parents, a tainted 

 pair who have no community of blood 

 will, so far as we know, be as likely to 

 have undesirable offspring as if they 

 were tainted cousins; whilst cousins 

 who are free from taint will be expected 

 to yield normal children. 



It must be said at once that the 

 data for answering the first question 

 upon statistical grounds do not exist 

 because no one up to the present time 

 has been able to obtain sufficiently 

 accurate returns of the relative numbers 

 of consanguineous and unrelated mar- 

 riages. 



FREQUENCY OF OCCURRENCE 



In 1862 a French writer, M. Boudin, 

 came to the conclusion that close 

 upon 1% of the marriages in France 

 between the years 1853 and 1859 were 

 between first cousins (counting in a 

 few between uncle and niece or aunt 

 and nephew.) And he considered that 

 if second-cousin marriages had been 

 included the total percentage would 

 be 2% This conclusion was based 

 upon the official records of more than 

 twenty million marriages. It is obvious 

 that such a return would err, if at all, 

 on the negative side; especially in a 

 CathoHc country such as France was 

 then. In the Roman Catholic Church 

 marriage between near cousins is for- 

 bidden unless an indulgence be obtained 

 by pa>TTient ; and obviously the liability 



1 Dr. Nettleship died shortly after preparing this paper, which was pubHshed in the Eugenics 

 Review, VI, 2, 130, London, July, 1914. It is here reprinted slightly abridged. 



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