THE LAWS OF NAUDIN-MENDEL 



An Interpretation of the Statistics of Pearson, Nettleship and Usher, on Albinism 



in Man Practical Rules to Regulate Marriage of Members of 



Tainted Family Stocks.' 



Dr. E. Apert 



Physician of the Hospitals of Paris, France. 



1BEG your pardon, gentlemen, for 

 returning to this subject of the ap- 

 jjlication of the laws of Naudin- 

 Mendel to the human species. I 

 have previously discussed the question 

 in my book Maladies Familiales; I have 

 treated it in various magazine articles; 

 I expounded it again at the International 

 Eugenics Congress in London. I would 

 not come back to it this time if it did 

 not seem to me absolutely necessary to 

 do so. These laws are the very founda- 

 tion of studies on heredity; they con- 

 stitute the clue which at last saves us 

 from losing ourselves in a chaos of 

 facts that at first sight are multiple, de- 

 ceptive and contradictor}'; thanks to 

 them, we may dream of establishing a ra- 

 tional science of eugenics; if they do 

 not corres]jond to the facts, we have no 

 basis on which to i)ursue our eugenic 

 studies. 



We must be very certain, then, of 

 the legitimacy of their application to 

 the human species. This legitimacy has 

 very recently been once more called in 

 question. Happily new data permit me 

 to establish the laws this time, not by 

 analogy, by generalization for man 

 from observations on lower animals, 

 but by direct demonstration. 



Let me recall that as a result of the 

 observ^ations of Naudin and Mendel 

 on crosses between varieties of the same 

 species of plant, and as a resvUt of more 

 recent confirmatory studies, we thought 

 we could consider the conclusions of 

 their studies as definitely established. 

 These conclusions were the segrega- 

 tion of forms in the posterity of crosses 



(Naudin), and the existence of definite 

 mathematical proportions between the 

 numbers of descendants belonging to each 

 of the segregated forms (Mendel). As 

 these laws had been verified in very 

 diverse species of plants and animals, 

 and for very diverse morphological, 

 physiological and even pathological 

 characters,* their extension to the hu- 

 man species might have been thought 

 indisputable and undisputed, and their 

 ap]3lication to the field of eugenics, 

 which I have tried to make, might have 

 been thought wholly legitimate. 



ATTACKS ON THE LAWS. 



But the legitimacy of the application 

 of the Naudin-Mendel Laws to the 

 human species has not only been called 

 in question, but violenth' disputed. An 

 article by Dr. Guyenot, " Mendelism 

 and Heredity in Man," published in his 

 excellent journal Biologica (Jan., 1914), 

 brings together a long list of objections 

 of the most diverse application. These 

 critics, it must be said, either limit 

 themselves to the abuses which may 

 occur in the premature aijplication to 

 particular cases, of princijjles which 

 remain none the less unshakeable, or 

 else waste their energy on the category 

 of cases which I emphasized at London. 

 In some cases the law of Mendel seems 

 to fail, because various other factors add 

 their influence to the hereditary fac- 

 tors governed by that law: such, for 

 example, is the sexual factor (matri- 

 archal heredity). To settle such cases, 

 one method alone is practicable — 



' Delivered before the Soci<5t6 Francaise d'Eug(5nique, Mav 6, 1^14; translated from Eugoniqiie 

 (organ of the society), II, 5, 129ff., Mai, 1914. 



* Hereditary ataxy in mice, rust resistance in wheat. 

 492 



