G ALTON AND STATISTICAL STUDY OF INHERITANCE 1 75 



reported, with a deaf parent; there are 12 families in which both 

 parents have deaf relatives of the same generation ; 1 1 in which 

 one parent has deaf relatives of the same generation ; and 3 in 

 which neither parent has deaf relatives of the same generation. 



This illustration proves that the origin of an individual pecu- 

 liarity has much to do with the question of its inheritance, and that 

 we cannot be sure that statistical data illustrate inheritance unless 

 we can separate the phenomena of ancestry from those of nurture. 



Furthermore, in order to prove that children always revert to 

 the mean or type of the race, and are on the average more medi- 

 ocre than their parents, we must prove that this is the case when 

 both parents have the same inherited peculiarity. Galton shows 

 that this is true of the stature of children both whose parents 

 were tall or both short, but he has not shown that it is true 

 when the peculiarity in the stature of both parents is the same 

 inherited peculiarity. He points out that stature may be affected 

 by diversity in the thickness of more than one hundred bodily 

 parts, and it is plain that if the extra height of a tall father is 

 due, for example, to a long femur, the chances are a hundred to 

 one that the femur of the tall mother is normal, and that her 

 extra height is due to some other peculiarity — thick intervertebral 

 bodies, for example. 



There is statistical evidence from other sources to show that 

 if both the parents have long femurs and have brothers and sis- 

 ters with long femurs, the children, instead of reverting to medi- 

 ocrity, may be expected to have, on the average, femurs very 

 much above the mean, and that some of them may have them 

 longer than either parent. 



Many facts in our stock of information regarding domesticated 

 animals and cultivated plants show that hereditary peculiarities 

 are often very persistent independently of selection, and the expe- 

 rience of all breeders shows that this tendency is greatly intensified 

 when both parents have the same inherited peculiarity. Not only is 

 this the case, but it may be proved by many observations that the 

 normal or type to which the average children of exceptional parents 

 tend to revert may itself be rapidly modified. In proof of this 

 I refer to the following experiments in selection by Fritz Miiller, 

 ("Ein Zuchtungs-versuch an Mais," Kosnios, 1886, 2, i, p. 22) : — 



