PHYSICAL CHARACTERS IN MAN 29 



legs. A child may happen to inherit all the relatively 

 long or short segment-lengths of its two parents, and 

 may thus be considerably taller or shorter than either 

 parent. Thus uniformity is not to be expected in 

 marriages between tall and short people. I know 

 personally of two cases of marriages between a very 

 exceptionally tall man and an exceptionally short 

 woman. In one case the son is tall, though not so 

 tall as his father. In the other, the son is exception- 

 ally short, like his mother. 



Castle (1922) has recently criticised these con- 

 clusions of Davenport. He made a study of size 

 inheritance in crosses between large and small varieties 

 of rabbits and found the F^ generations intermediate 

 between the parental races, but nearer the size of the 

 larger parent owing to heterosis or hybrid vigour. 

 The latter phenomenon is well known. It is largely 

 confined to the F^ of both plant and animal hybrids, 

 and probably occurs also in some first generation 

 crosses of man.* Castle found that in crosses between 

 two small varieties of rabbits, such as Polish and 

 Himalayan, the F^ was larger than either parent 

 owing to this " hybrid vigour," but the effect was lost 

 in the F2, which was strictly intermediate in average 

 size. In crosses of either of these races with the 

 much larger Flemish rabbit, the average size of the 

 F2 was strictly intermediate, but the range of varia- 

 tion was much greater than in F^. By the application 

 of statistical methods it was estimated that eight or 

 ten independent factors or linkage-systems affected 

 the size. 



Extensive measurements were made of weight, 

 ear-length, and the dimensions of several bones. A 

 study of the correlation between these measure- 

 ments was made, in order to determine whether 



* For a discussion of heterosis in hybrids see East and Jones 

 (1919)- 



