THE PURE LINE 



101 



Finally, the relation between the midparent and 

 the average offspring may be expressed in fractional 

 form by taking the average height of the offspring 

 for the numerator and the height of the midparent 

 for the denominator in each instance. The minus 

 deviations are thus seen to be 



4 2.5 1.5 1 

 6 4.5 2 1.5 



which, added together and reduced to a decimal, 

 equal .60. 



Similarly, the plus deviations are 



J_ _L5 2 5.5 

 1.5 3 4.5 6 



which reduce to .63. The average of the minus 

 deviations (.60) and the plus deviations (.63) is 

 nearly .62, or about two thirds. 



That is to say, the fraction f represents the 

 amount of resemblance or "inheritance" between two 

 generations, as determined by the foregoing series, 

 while the remaining I is the measure of "regression" 

 from the general type. 



This illustrates Galton's Law of Regression or the 

 tendency in successive generations toward medioc- 

 rity. The law may be stated as follows : - 



