62 2 POPULAR SCIENCE MONTHLY. 



congenitally deaf and the state of the hearing of the wives is un- 

 known produced congenitally deaf children. 



Of the twenty-six families in which both parents are deaf and 

 have congenitally deaf children, there are five families in which 

 one of the parents has one deaf parent, seventeen families in 

 which both parents have deaf relatives of the same generation, 

 four in which one parent has deaf relatives of the same genera- 

 tion, and five in which neither parent has deaf relatives of the 

 same generation. 



Of the twenty-six families in which both parents are congeni- 

 tally deaf and have hearing children only, there is none in which 

 either parent has a deaf parent, so far as reported, twelve families 

 in which both parents have deaf relatives of the same generation, 

 eleven families in which one parent has deaf relatives of the same 

 generation, and three families in which neither parent has deaf 

 relatives of the same generation. 



This illustration proves that the origin of an individual pecul- 

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

 that we can not be sure that statistical data illustrate inheritance 

 unless we can separate 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 to a long femur for example, the chances are a hun- 

 dred to one that the femur of the tall mother is normal and that 

 her extra height is due to some other peculiarity thick interver- 

 tebral bodies, for example. 



There is statistical evidence from other sources to prove that 

 if both parents have long femurs and have brothers and sisters 

 with long femurs, the children, instead of reverting to mediocrity, 

 may on the average be expected to have 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 domestic 

 animals and cultivated plants show that hereditary peculiarities 

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

 perience of all breeders shows that this tendency is greatly inten- 

 sified when both parents have ilie same inherited peculiarity. 



