FERTILITY 605 



The inheritance of fertility in Man and also in thoroughbred 

 horses has been investigated statistically by Karl Pearson and 

 his biometrical collaborators, 1 to whose memoir the reader is 

 referred for a full discussion of the mathematical details and 

 the conclusions which are arrived at. It is there shown, 

 among other facts, that the woman inherits fertility equally 

 through the male and female lines. Among thoroughbred 

 race-horses the fecundity was first ascertained (i.e. the ratio 

 of foals surviving to be yearlings to the total number of foals 

 possible under the given conditions), and the following general 

 conclusions were afterwards reached : (1) Fecundity is inherited 

 between dam and daughter, and (2) Fecundity is also inherited 

 through the male line, i.e. the sire hands down to his daughter 

 a portion of the fertility of his dam. Thus fecundity, which is, 

 of course, a latent character in the male, was measured for a 

 horse and for his sire, and was found to be strongly inherited. 



More recently Rommel and Phillips 2 have shown mathe- 

 matically that there is an actual correlation between the size of 

 the litter in two successive generations of Poland China sows, 

 the productiveness being a character which is transmitted from 

 mother and daughter. 



On the other hand Pearson 3 from studying Weldon's records 

 of mice-breeding experiments, failed to find a sensible parental 

 correlation in regard to the size of the litters. Furthermore, 

 Pearl and Surface, 4 as a result of a statistical investigation on 

 egg-production in Barred Plymouth Rock fowls, carried on over 

 nine years, found no evidence of the inheritance of fecundity. 

 For this particular breed at any rate the capacity for egg-pro- 

 ducing could not be increased by selective breeding, but tended 



1 Pearson, Lee, and Bramley- Moore, " Mathematical Contributions to the 

 Theory of Evolution : VI., Genetic (Reproductive) Selection, Inheritance of 

 Fertility," &c., Phil. Trans., A., vol. cxcii., 1899. 



2 Rommel and Phillips, " Inheritance in the Female Line of Size of 

 Litter in Poland China Sows," Proc. Ann,-. 1'hil. .sv-., vol. xlv., 1907. 



3 Pearson, " On Heredity in Mice, from the Records of the late W. F. R. 

 Weldon," Biometrika, vol. v., 1907. 



4 Pearl and Surface, " Data on the Inheritance of Fecundity obtained 

 from the Records of Egg Production," &<.. Mnim .!<///<. /.'</<. Station, 

 Bulletin No. 166; Maine, 1909. Pearl, "A Biometrical Study of Egg Pro- 

 duction in the Domestic Fowl," 17. S. Dep. of .-!;///<.. linn mi of Animal 

 Industry, Bulletin No. 110; Washington, 1909. 



