76 



HEREDITY 



considerable influence. In the first place, there are 

 probably many different hereditary factors having an 

 influence in the matter. The number of hybrid char- 

 acters as influencing physiological vigour may probably 

 bear some relation to it. Finally, stature is to some 

 extent influenced by environmental conditions, such as 

 nutrition, cUmate, accidental injuries, disease, and so 

 forth. Such a large group of independent causes tends 

 to produce normal variability. 



In studying the inheritance of stature by the 

 statistical method, we make no effort to separate the 

 effects of these vai'ious causes, but simply set out to 

 discover the average degree of gross difference or re- 

 semblance between parent and child. 



Our first business is to make several hundreds of 

 observations of the stature of, say, father and son. 

 This done, we proceed to arrange the figures in groups. 

 Taking, say, all the fathers between 61^ and 62^ inches, 

 we may set them down as a group at 62, and proceed 

 to set do\\Ti in groups the statures of the sons of these 

 several fathers, finally striking an average of the lot. 

 Thus in the investigation carried out by Professor 

 Pearson and Miss Lee, where over a thousand pairs of 

 fathers and sons were measured, there were seventeen 

 fathers in the 62-inch group. The sons of these, ar- 

 ranged in groups to the nearest inch, were as follows : — 



2 



4 

 2 

 2 



5 

 2 



giving the average size of about 65J inches. 



One proceeds in a similar manner with all the groups 

 of fathers which in the investigation mentioned extended 

 from 59 to 75 inches, ascertaining the average size of 

 the sons of each group. It is now possible to express 

 these figures grapliically. On squared paper, one can 

 set off, say, horizontal distances to represent the several 



