320 STATISTICAL STUDY OF INHERITANCE 



an average height differing but Httle from that indicated by the 

 formula. In regard to all these statistical conclusions, it must 

 be carefuUy borne in mind that they cannot be applied to 

 individual cases. " Of the individual we can assert nothing as 

 certain, only state the probable. The individual varies owing 

 to the variability of the gametes, and we know nothing of the 

 particular gametes which fused to give the stirp, of which 

 he is the product. All we know in heredity is what degree 

 of resemblance there is on the average. . . . The statistician 

 dealing with heredity is like the physicist dealing with the 

 atom — he can say little or nothing of the individual, his know- 

 ledge is of the group containing great numbers." (Pearson, 

 op. cit, p. 457.) 



Note on the Term Regression.— As the term regression, used 

 by Galton to describe the extent to which an average son is more 

 like the mean of the stock than his father is, has been often 

 misunderstood to imply something in the nature of a "throw- 

 back," it is probably desirable to get rid of it and to substitute 

 for it the technical term correlation, which expresses the extent 

 to which a son approximates nearer to his father than to the 

 average of the stock. 



The term " regression " which Mr. Galton introduced into 

 biometrics is not really a biological term. As the late Prof. 

 Weldon pointed out in an interesting lecture, there may be 

 regression between two different sets of results of dice-throwing 

 if the second set of results is in some way, but not entirely, 

 dependent upon the first. He protested against regarding 

 regression " as a peculiar property of living things, by virtue 

 of which variations are diminished in intensity during their 

 transmission from parent to child, and the species is kept true 

 to its type (1906, p. 107). This view may seem plausible to 

 those who simply consider that the mean deviation of children 

 is less than that of their fathers ; but if such persons would re- 

 member the equally obvious fact that there is also a regression 



