102 SEX AND HEREDITY 



normals. Hence we have the following possibilities in 

 syngamy : 



Gametes of Brachydactylous Gametes of Normal 



Persons. Persons. Zygotes. 



Brachydactylous x Normal Brachydactylous. 



Normal x Normal Normal. 



Thus the result of the marriage of brachydactylous and 

 normal persons should be, on the average, half the children 

 brachydactylous and half normal a result which is 

 approximately realised in the pedigree. 



However, for the reasons indicated above, Mendel's 

 law will not take us very far in the investigation of 

 inheritance in man, and different methods have to be 

 employed which, while they may not have added much 

 to our knowledge of the how and why of inheritance, have 

 resulted in the discovery of formulae which describe in 

 a simple way the relation between parent and offspring 

 for a large number of characteristics. 



The invention and development of these methods is 

 almost entirely due to Sir Francis Galton and Professor 

 Karl Pearson. The methods are much too elaborate 

 and require far too advanced a knowledge of mathe- 

 matics to attempt to describe here, but the general way 

 of attacking the problem and the main results are 

 easily intelligible. 



To begin with, we will take the inheritance of height 

 or stature, using the data provided by Pearson's measure- 

 ment of over 1000 families. In this case we will limit 

 ourselves to fathers and sons, as the results are practically 

 identical for mothers and daughters, and indeed for fathers 

 and daughters and for mothers and sons. 



In Table I the left hand column gives the heights of 

 the fathers (in inches) and the third column the average 

 height of their sons. The other two columns show the 



