The Editor: Genealogy and Eugenics 



379 



here genealogy can aid with very Httle 

 trouble. Unfortunately, it is not un- 

 common to find in the earHer genera- 

 tions of a family tree that the exact 

 birth-rank of the various children is 

 not designated; nor is account always 

 made of infant deaths or still-births, as 

 should certainly be done in every case. 



The question of consanguineous mar- 

 riage is one in which every genealogist 

 is certain to have taken an interest, 

 merely because of the doubling up of a 

 name in his chart, if not from a biological 

 point of view. Until recently, the 

 question of the marriage of kin was 

 debated largely by an appeal to dogma. 

 I daresay every genealogist has seen 

 cases where the marriage of first cousins 

 was followed by good progeny, and 

 equally cases where the result was bad. 

 There is plenty of evidence of that sort 

 to be had on both sides. I think it is 

 safe to say that genetics has established 

 the status of consanguineous marriage 

 beyond all dispute. It certainly is not 

 bad in itself, although first cousins are 

 forbidden by law to marry in a third of 

 the States of the Union. i'^ It simply 

 results in a doubling up of the traits 

 which the two may have in common. If 

 these traits are good, the children get 

 a double dose of them, and will be more 

 highly endowed than their parents. If 

 the traits are bad, the children equally 

 get a double dose of them, and may far 

 surpass their parents in worthlessness, 

 or in the prominence of any particular 

 defect. The general conclusion is clear 

 to us: marriages between cousins or 

 other relatives of equal consanguinity, 

 should not be condemned offhand, but 

 the facts should be taken into considera- 

 tion in each individual case. And it 

 should be borne in mind, of course, 

 that a trait may be latent or concealed 

 in each of the cousins, but come into 

 expression in their children. Although 

 cousin marriages, therefore, should be 

 scrutinized closely, we certainly find no 

 reason to forbid them when the con- 

 tracting parties are of sound stock. 



The question of the inheritance of 

 disease is one of great importance, 

 which can be studied very easily through 



genealogy. Of course, no one with a 

 knowledge of modern work in genetics 

 now believes that diseases are truly 

 inherited as such; but there is a great 

 deal of evidence to show that what the 

 doctors call a "diathesis," a predisposing 

 tendency to some disease, may be 

 inherited. Greater research is urgently 

 needed to find the extent and limits of 

 such inheritance, and it is to enlightened 

 genealogy that we must look for the 

 solution of the problem — or rather, 

 problems, since there are as many 

 problems as there are diseases, defects 

 and abnormalities. We must not draw 

 hasty generalizations, but attack each 

 subject separately. We have pretty 

 good evidence, for instance, that the 

 tubercular diathesis is inherited: that 

 the white plague ravages some families 

 and leaves others untouched; that al- 

 most every city-dweller, at least, is at 

 some time or other during his life in- 

 fected with phthisis, and whether he 

 resists or succumbs depends on his 

 heredity. Herein lies guidance for those 

 who would marry: other things being 

 equal, let them avoid the weak stocks, 

 the stocks known to be marked by 

 tuberculosis. But because tuberculosis 

 is thus a matter of heredity, it does not 

 necessarily follow that cancer, or any 

 other disease, is. We must take nothing 

 for granted ; we must find out by examin- 

 ing many families in which a given 

 disease or abnormality occurs. And to 

 do this, we must depend on the data of 

 genealogy. 



Here, however, let me utter an em- 

 phatic warning against superficial inves- 

 tigation. The medical profession has 

 been particularly hasty, many times, 

 in reporting cases which were assumed 

 to demonstrate heredity. The child 

 was so and so; it was found on inquiry 

 that the father was also so and so: 

 post hoc, ergo propter hoc — it must have 

 been heredity. Such a method of 

 investigation is calculated to bring the 

 science of genetics into disrepute, and 

 might easily ruin the credit of the science 

 of genealogy, should genealogy allow 

 itself to be so misled. As a fact, one 

 case counts for practically nothing as 



" Davenport, C. B. State Laws Limiting Marriage Selection, p. 14. Eugenics Record Office 

 Bull. No. 9, Cold Spring Harbor, Long Island, N. Y., June, 1913. 



