Apert: The Laws of Naudin-Mendel 



493 



namely, the patient observation of 

 numerous cases of inheritance in man. 



Of course, the objection is at once 

 raised that it is very difficult to observe 

 the facts of heredity in man. The dif- 

 ficulties are indeed great, and there is 

 every reason for insisting on them. 

 The observation of facts of heredity can 

 be much simplified in experimental 

 plant and animal breeding, by judicious 

 choice of the varieties with which one 

 works, but no such expedient is avail- 

 able in the hiunan species. It is very 

 true, as critics have emphasized, that 

 scientific prudence requires us, in deal- 

 ing with heredity in man, sometimes to 

 have a doubt about the real paternity 

 of the subjects with whom we are deal- 

 ing. It is very true that it is hard to 

 push our researches farther back than 

 two or three generations. It is very 

 true that the ordinarily small number 

 of descendants of any couple make the 

 search for the Mendelian proportions 

 deceptive. All of these difficulties are 

 of the most inevitable sort. But be- 

 cause the verification of a law is dif- 

 ficult, shall we say that the law is 

 untrue? Hardly! We are merely led to 

 say that researches on a large scale 

 are necessary to surmount the difficul- 

 ties, and to verify or contradict the 

 exactitude of the law. The work will 

 be onerous, but may nevertheless be 

 conclusive. 



A good part of this work of collecting 

 facts is now in process, thanks to the 

 efforts of eugenic organizations. I do 

 not refer to our own society, whose 

 birth is too recent and whose funds too 

 limited, to allow it to do such work; 

 but you are familiar with the beautiful 

 publications which make up the Treas- 

 ury of Human Inheritance, issued by 

 the Eugenics Laboratory of London, 

 and also with the Drapers' Company 

 Research Memoirs, published by the 

 Biometric Laboratory of the University 

 of London. In the latter series, Messrs. 

 Pearson, Nettleship and Usher have 

 just issued a big volume of pedigrees 

 relating to albinism in man. 



ALBINISM IN MAN. 



Albinism is one of the variations 

 which has been the most studied from 



the top to the bottom of the animal and 

 vegetable scale, from the Mendelian 

 point of view, and it has always s'hown 

 itself to be recessive from that point of 

 view. Here, then, is a good chance to 

 see whether albinism obeys Mendel's 

 Law in man, too; whether it is reces- 

 sive, as it is with other living things. 

 When it is realized that the work of 

 these writers has brought together 691 

 genealogical trees, that many of them 

 include three, four, five, or even six 

 generations, that some of them include 

 several hundred individuals, it will be 

 admitted that the material on hand 

 makes errors, if not negligible, at 

 least much less important, so that their 

 final influence on the results will be 

 very slight. 



In particular, the objection drawn 

 from the small number of offspring of 

 a single couple, in the human species, 

 wholly disappears. If, instead of seek- 

 ing the number of albinos among the 

 offspring of a single couple, we seek the 

 number among the children of some 

 hundreds of couples, all of whom have 

 given rise to one or more albinos, the 

 result obtained will command some re- 

 spect ; and if it coincides with the Men- 

 delian proportions, we have a right to 

 assume that the law of Mendel is veri- 

 fied. 



However, we do not obtain the large 

 mmibers necessary if we limit ourselves 

 to investigating the direct descendants 

 of albinos. For many reasons, albinos 

 rarely marry; and their marriages are 

 rarely fecund. Fertile marriages be- 

 tween two albinos are rare ; in marriages 

 between an albino and a normal the 

 result is, according to the Mendelian 

 law, variable according as the normal 

 individual is homozygous (in that case 

 there should be no albino offspring, 

 according to the formula DDxRR = 

 100% DR), or as that individual is 

 heterozvgous (when we have DRx 

 RR = 56% DR+50% RR, or half of 

 the children albinos). But in man, it 

 is rare that we can say with certainty 

 whether a subject of normal appearance 

 is or is not homozygous. We can, there- 

 fore, get no help for our present study 

 from statistics of children one of whose 

 parents was albino and the other nor- 



