TWINS AND HEREDITY 



in au NN AR I) AH LB ERG 



INSTlTL'TIi OF HACK RIOI.OGY, UPPSALA 



ON the initiative of Professor Lundrohg some preliminary studies 

 have heen made in the Uterature hearing on the question of twins 

 born from one ovum and from two ova, and as to whether twin-hirth 

 is inherited. As it seems to me that this question of the inheritance 

 of twin-hirth has l)een phued in a false position, perhaps a few 

 remarks may be eonsidered justified at present. 



The foundation in this field of research has been laid by Weinberg, 

 who came to the conclusion that the power of producing twins from 

 two ova is. inherited, w hile the inheritance of the capacity of producing 

 twins from a single ovum could not be proved. Weinberg expresses 

 his views very modestly, but later writers have generalized his conclu- 

 sions in rather a careless manner. The view held by Weinberg that 

 the power of giving birth to twins from two ova is inherited while 

 the inheritance of twin-birth from one ovum is uncertain has been 

 quoted as being a more or less established fact by such investigators as 

 Prinzing, Rumpe and Bonnevie. Writers of text-books speak only 

 of twins in general without differentiating between such from one ovum 

 or from two. Lenz, apparently from purely theoretical motives and 

 without adding any new facts, assumes the inheritance of twin-birth 

 from both one ovum and from two. 



In his first work, in 1904, Weinberg inserts the following table 

 and draws his conclusions in the following manner: — - 



»A subtraction gives the following numbers for births from one 

 ovum: 1987 — 778 = 1209 cases in 5645 births and 64 pairs of twins. 



Among the relatives of two ova twin-births are found in a ratio 

 of 1 : 44. The corresponding ratio for twins from one ovum is 1 : 88. 

 This difference is very significative. The number of births from one 

 ovum corresponds very nearly with the percentage for the whole 

 population, the frequency of twins in Stuttgart being in ratio of 1 : 92. 



So far, therefore, the inheritance of the capacity of giving birth 

 to twins can be shown only in the case of two-egg twins.» 



Weinberg uses here his differentiation method. He starts from the 

 supposition that, with the birth of twins from two ova, the sex of 



