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The Journal of Heredity 



to such an exaction would sometimes 

 lead to concealment of cousinship. 

 Somewhat later returns (up to 1875) 

 showed a rather higher proportion 

 (1.5%) of first-cousin marriages, the 

 consequence, apparently, of instruc- 

 tions from headquarters to make 

 the enquiries more thorough. Further, 

 M. Lego^i; (Chief of the Statistical 

 Department for France, quoted by 

 George Darwin), at about the same date, 

 came to the conclusion that the true 

 percentage of first-cousin marriages for 

 the whole of France was much higher 

 than Boudin had supposed, viz., about 



3%. 



In 1875 George Darwin juiblished a 

 long and careful paper upon " Marriages 

 of First Cousins in England and Their 

 Effects." In this memoir the author 

 made the important point that in 

 England and Wales cousin marriages 

 are probably much more frequent, rela- 

 tively, in the aristocracy than in the 

 general population, and least frequent 

 in London. He estimated that 3.5% of 

 aristocratic marriages were between first 

 cou.sins, but only 1.5% of all London 

 marriages. The paper was the outcome 

 of great labor and care, but the exact 

 figures of the cousin marriages were 

 admittedly open to revision. 



In 1908 Professor Karl Pearson made 

 a limited contribution to the subject. 

 He found that of 1,600 members of the 

 medical profession no less than 4.5% 

 had married first cousins, and that 

 if the lesser degrees of consanguinity 

 were included the total was 7.5%. 



This 4.5% of first-cousin unions may 

 be comy)ared with Legoyt's estimate of 

 about 3% for the whole of France, and 

 George Darwin's 3.5% for the British 

 aristocracy. 



Pearson further, horn an examination 

 of the books of the hosjjital for sick 

 children in London, found only 1.3% 

 of cousin marriages of all degrees 

 up to third cou.sins, recorded in the 

 histories of 700 in-patients. This so 

 far as it goes confirms George Darwin's 

 conclusion that consanguineous mar- 

 riage was relatively infrequent in Lon- 

 don; but the family histfjries of these 

 700 hospital in-imtients were jjrobably 



far from complete in regard to the point 

 and 1.3% is almost certainly too low. 



DISCREPANCIES IN DATA 



From these discrepant, and avowedly 

 incomplete, materials it seems probable 

 that a class or clan or caste influence 

 operates in certain cases to produce a 

 high proportion of consanguineous mar- 

 riages, and therefore conclusions as to 

 any effects of consanguinity, whether 

 bad or good, drawn from a mass popula- 

 tion would not necessarily apply to all 

 the groujjs of which the population was 

 composed. However this may be, one 

 certainly finds that in some individual 

 genealogies cousins often marry, and 

 in others seldom or never. 



As to the second question: Are the 

 defects sometimes observed in the 

 offspring of consanguineous parents 

 due to the consanguinity as such or on 

 the other hand to both parents being 

 tainted ? 



In regard to the de novo origin of 

 defects in children of cousin parentage 

 we find Charles Darwin stating his 

 belief as follows, after having devoted 

 much attention to the subject: "I hope 

 to show in a future work that con- 

 sanguinity by itself counts for nothing, 

 but acts solely from related organisms 

 having a similar constitution, and having 

 been exposed in most cases to similar 

 conditions;" and a recent authority, 

 Professor J. Arthur Thomson, of Aber- 

 deen, considers that "the idea that there 

 can be any objection to the marriage of 

 two healthy cousins who happen to fall 

 in love with one another is preposter- 

 ous." Many similar, and also some, but 

 I think a diminishing number of, opi)o.s- 

 ing, opinions might be cited. 



What then is the origin of the view, 

 or at least the suspicion, held by many, 

 that consanguineous unions are injurious 

 as such? 



Without going back to the very 

 early history of marriage customs and 

 ]irohibitions — a task I am not comj^etent 

 to undertake — it is I think enough to 

 say that the early Christian Church 

 ajjjicars to be chiefly responsible for 

 the existing residue of prejudice against 

 the marriage of cousins. The church 

 put its ban upon consanguineous unions ; 



