Septembeb i, 1914] 



SCIENCE 



323 



destination. It, moreover, exemplifies that 

 parental polarity of the zygote to which I 

 alluded in my first address, a phenomenon 

 which we suspect to be at the bottom of 

 various anomalies of heredity, and sug- 

 gests that there may be truth in the popular 

 notion that in some respects sons resemble 

 their mothers and daughters their fathers. 



As to the descent of hereditary diseases 

 and malformations, however, we have 

 abundant data for deciding that many are 

 transmitted as dominants and a few as re- 

 cessives. The most remarkable collection 

 of these data is to be found in family his- 

 tories of diseases of the eye. Neurology 

 and dermatology have also contributed 

 many very instructive pedigrees. In great 

 measure the ophthalmological material was 

 collected by Edward Nettleship, for whose 

 death we so lately grieved. After retiring 

 from practise as an oculist he devoted sev- 

 eral years to this most laborious task. He 

 was not content with hearsay evidence, 

 but traveled incessantly, personally exam- 

 ining all accessible members of the families 

 concerned, working in such a way that his 

 pedigrees are models of orderly observa- 

 tion and recording. His zeal stimulated 

 many younger men to take part in the 

 work, and it will now go on, with the re- 

 sult that the systems of descent of aU the 

 common hereditary diseases of the eye will 

 soon be known with approximate accuracy. 



Give a little imagination to considering 

 the chief deduction from this work. Tech- 

 nical details apart, and granting that we 

 can not wholly interpret the numerical re- 

 sults, sometimes noticeably more and some- 

 times fewer descendants of these patients 

 being affected than Mendelian formulae 

 would indicate, the expectation is that in 

 the case of many diseases of the eye a large 

 proportion of the children, grandchildren, 

 and remoter descendants of the patients 

 will be affected with the disease. Some- 



times it is only defective sight that is 

 transmitted; in other cases it is blindness, 

 either from birth or coming on at some 

 later age. The most striking example, per- 

 haps, is that of a form of night-blindness 

 still prevalent in a district near Montpel- 

 lier, which has affected at least 130 persons, 

 all descending from a single affected indi- 

 viduaP who came into the country in the 

 seventeenth century. The transmission is 

 in every case through an affected parent, 

 and no normal has been known to pass on 

 the condition. Such an example well 

 serves to illustrate the fixity of the rules of 

 descent. Similar instances might be re- 

 cited relating to a great variety of other 

 conditions, some trivial, others grave. 



At various times it has been declared that 

 men are born equal, and that the inequality 

 is brought about by unequal opportunities. 

 Acquaintance with the pedigrees of dis- 

 ease soon shows the fatuity of such fancies. 

 The same conclusion, we may be sure, 

 would result from the true representation 

 of the descent of any human faculty. Never 

 since Galton's publications can the matter 

 have been in any doubt. At the time he 

 began to study family histories even the 

 broad significance of heredity was fre- 

 quently denied, and resemblances to par- 

 ents or ancestors were looked on as inter- 

 esting curiosities. Inveighing agaiast 

 hereditary political institutions, Tom Paine 

 remarks that the idea is as absurd as that 

 of an "hereditary wise man," or an "hered- 

 itary mathematician," and to this day I 

 suppose many people are not aware that 



2 The first human descent proved to follow Men- 

 delian rules was that of a serious malformation of 

 the hand studied by Farabee in America. Drink- 

 water subsequently worked out pedigrees for the 

 same malformation in England. After many at- 

 tempts, he now tells me that he has succeeded in 

 proving that the American family and one of his 

 owu' had an abnormal ancestor in common, five 

 generations ago. 



