CHAPTER IV 



THE STATISTICAL STUDY OF HEREDITY 



In studying heredity, either of two methods may 

 be adopted. We may either choose a character and 

 observe or measure its development in a large number 

 of parents and in their childi'en, and so deduce the 

 average extent of resemblance between parents and 

 children for that character ; or we may consider a 

 number of individual cases separately, and endeavour 

 to discover the manner in which the character appears 

 in the children who have parents or ancestors pos- 

 sessing it. With regard to the first method Prof. 

 Pearson has written * We must proceed from inheri- 

 tance in the mass to inheritance in narrower and 

 narrower classes, rather than attempt to build up 

 general rules on the observation of individual in- 

 stances.' And ', . .the very nature of the distribution 

 ...seems to indicate that we are dealing with that 

 sphere of indefinitely numerous small causes, which 

 in so many other instances has shown itself only 

 amenable to the calculus of chance, and not to 



