viz.] DISCUSSION OF THE DATA OF STATURE. 97 



Statures of the Sons would be, if they were on the 

 average identical with those of their Mid- Parents. 



o 



Most obviously A B does not agree with C D ; therefore 

 Sons do not, on the average, resemble their Mid- 

 Parents. On examining these lines more closely, it 

 will be observed that A B cuts C D at a point M that 

 fairly corresponds to the value of 685- inches, whether 

 its value be read on the scale at the top or on that at 

 the side. This is the value of P, the Mid-Stature of 

 the population. Therefore it is only when the Parents 

 are mediocre, that their Sons on the average resemble 

 them. 



Next draw a vertical line, E M F, through M, and 

 let EGA be any horizontal line cutting ME at E, MC 

 at E, and MA at A. Then it is obvious that the ratio of 

 EA to EC is constant, whatever may be the position of 

 EGA. This is true whether E C A be drawn above or 

 like F D B, below M. In other words, the proportion 

 between the Mid-Filial and the Mid-Parental deviation 

 is constant, whatever the Mid-Parental stature may be. 

 I reckon this ratio to be as 2 to 3 : that is to say, the 

 Filial deviation from P is on the average only two- 

 thirds as wide as the Mid-Parental Deviation. I call 

 this ratio of 2 to 3 the ratio of " Filial Eegression." It 

 is the proportion in which the Son is, on the average, 

 less exceptional than his Mid-Parent. 



My first estimate of the average proportion between 

 the Mid-Filial and the Mid-Parental deviations, was 

 made from a study of the MS. chart, and I then 

 reckoned it as 3 to 5. The value given above was 



H 



