FERTILITY 643 



by breeding from twin ewes and employing the S.TVHT- of twin rams, 

 have been able permanently to increase the fertility of their stock. 1 



The inheritance of fertility in man and also in thorough bn-d 

 horses has been investigated statistically by Karl Pearson and his 

 biometrical collaborators,- to whose memoir the reader is referred for 

 a full discussion of the mathematical details and the com In 

 which are arrived at. It is there shown, among other facts, that the 

 woman inherits fertility equally through the male and female lim-s. 

 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 KM< hrd : (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 nir.omed for a horse and 

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



More recently Rommel and Phillips 3 have shown mathematically 

 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, I'earson, 4 from studying Weldon's records of 

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

 in regard to the size of the litters. I'earl and .Surface, 5 as a result of 

 a statistical investigation on egg-production in Jiarn-d 1'lvmoiith 

 Hock fowls, found no evidence of the inheritance of fecundity so long 

 as simple mass selection was practised. For this breed the capacity 

 for egg-producing was not increased by this method, but tended 

 rather to be diminished. 



Pearl next started to analyse his results on the assumption that 

 Mendelian factors might exist which were themselves concerned 

 with different degrees of fertility. He found that the winter egg- 

 production bore a direct relation to the total egg- production 



1 Mai-shall, "Fertility in Scottish Sii. ).. />.///.<. ///<//./<//./ //;./ . i 

 vol. xx., 1908. 



2 Pearson, Lee, and Bramley Moore, "Mathematical Contribution! i" tlie 

 Theory of Evolution: VI, (Jt-netic (ReprodncttTe) Srlirtion, Inln-ritan 

 Fertility, etc.," /'/-//. '/',.>/.<., A., vol. -x.-ii., l- 



3 Rommel and Phillips, Inheritance in tin- l-Ymalr I,ii f Si/-- of I-ittei- 



in P< 'land China Sows," /V<. .I,,,-,-. /'/,//. >'.., \..l. \1\.. I!o7. 



4 Pearson, "On Heredity in Mirr, from the Records of the late W. K. II. 

 Weldon," />'/<///////<, vol. v.', I'.xiT. 



IVarl and Surface. " Una on tin- [nheritance <>f fecundity obtained 



No. 110, Washington, 1900. 



