INFLUENCE OF THE MALE IN THE PBODUC- 

 TION OF HUMAN TWINS 1 



DR. C. B. DAVENPORT 

 Station for Experimental Evolution, Cold Spring Harbor, L. I. 



It is frequently pointed out that the father of twins 

 can have little influence in determining their production ; 

 such production is purely a maternal quality, due to 

 double ovulation. One possible way, however, in which 

 the male may influence twin production is recognized, but 

 this affects only 1-egg twins. Thus, if we assume that 

 1-egg twins are due to an early fission of the embryonic 

 blastodisc, or if they are due to a secondary budding (fol- 

 lowing the method of the armadillo), then the sperm cell 

 might carry the tendency to such fission or budding, as 

 well as the egg cell. This possibility, however, does not 

 help the statistical student of plural births, such as Wein- 

 berg, because he believes that the tendency to 1-egg twins 

 is not inherited at all. 



In the following study, there will be considered only 

 the class of cases showing heredity most clearly, namely, 

 those in which the principal fraternity under considera- 

 tion has more than one pair of twins. Parents of such 

 fraternities are spoken of in what follows as repeater 

 fathers or mothers. Our query is then: "What is the 

 relative importance in twinning of inheritance from the 

 maternal and paternal sides, or what is the relative oc- 

 currence of twin labors in the close relatives of repeating 

 mothers and of their husbands? " 



To get an answer to this question, all available figures 

 on twin repeaters were studied statistically. Of 355 

 labors occurring to the mothers of repeating mothers, 16 

 (4.5 per cent.) were twin labors. Of 289 labors occurring 

 to the mothers of twin-repeating fathers, 12 (4.2 per 

 cent.) were twin labors. These statistics thus indicate 



i Read before the American Society of Naturalists, at Princeton, Dee. 

 30, 1919. 



