Law of Regression 



mean whether that departure is due to a mutation 

 or a fluctuating variation. 



It is only by watching the effect of the 

 peculiarity on the offspring of its possessor that 

 we are able to determine the nature of the varia- 

 tion. Where the peculiarity is due to a fluctuating 

 variation the offspring will display the peculiarity 

 in a diminished degree ; but if the peculiarity be 

 due to a mutation, the offspring are likely to 

 display it in as marked a degree as the parent. 



Fritz Mliller and Galton conducted inde- 

 pendently enquiries into the amount of the 

 regression shown by the progeny of parents 

 which have deviated from the average by 

 fluctuating variation. 



Mliller experimented with Indian corn; Galton 

 with the sweet pea. 



Each found that where the deviation of the 

 parents is represented by the figure 5, that of 

 their offspring is usually 2, that is to say, the 

 deviation they display is, on the average, less 

 than half that of their parents. 



Applying this rule to the hypothetical case 

 given above, if two individuals of species A 

 having a length of wing of 20 inches be bred 

 together, their offspring will, on an average, have 

 a length of wing of 20 inches, since neither 

 parents showed any deviation from the mean. 

 On the other hand, the offspring of 2O-inch-wing 

 individuals of species B would show, on an 

 F 81 



