104 NATURAL INHERITANCE. [CHAP. 



crown of the head, upwards or downwards as the case 

 may be, and not from the ground to the crown of the 

 head. (In the population with which I am now dealing, 

 the level of mediocrity is 68J inches (without shoes).) 

 The law of Regression in respect to Stature may be 

 phrased as follows ; namely, that the Deviation of the 

 Sons from P are, on the average, equal to one-third of 

 the deviation of the Parent from P, and in the same 

 direction. Or more briefly still : If P + (=t D) be the 

 Stature of the Parent, the Stature of the offspring will 

 on the average be P + (=t 3- D). 



If this remarkable law of Regression had been based 

 only on those experiments with seeds, in which I first 

 observed it, it might well be distrusted until otherwise 

 confirmed. If it had been corroborated by a compara- 

 tively small number of observations on human stature, 

 some hesitation might be expected before its truth could 

 be recognised in opposition to the current belief that the 

 child tends to resemble its parents. But more can be 

 urged than this. It is easily to be shown that we ought 

 to expect Filial Regression, and that it ought to amount 

 to some constant fractional part of the value of the Mid- 

 Parental deviation. All of this will be made clear in a 

 subsequent section, when we shall discuss the cause of 

 the curious statistical constancy in successive generations 

 of a large population. In the meantime, two different 

 reasons may be given for the occurrence of Regression ; 

 the one is connected with our notions of stability of 

 type, and of which no more need now be said ; the 

 other is as follows : The child inherits partly from his 



