THE STUDY OF INHERITANCE. 617 



THE STUDY OF INHERITANCE. 



A Review of the Writings of Francis Galton. 

 BY W. K. BEOOKS, LL. D. 



SECOND PAPER. 



IT may be well to remind those who are not familiar with 

 statistical reasoning that a type may exhibit the influence of 

 inheritance and yet be of no value as a basis for generalization on 

 inheritance. 



The bullet type shows the influence of aim, but if we use it to 

 test the accuracy of aim or the excellence of the rifle we may 

 be led astray if some other influence, such as the weight of the 

 bullet, act on all or on a majority of the shots and escape detec- 

 tion. In this case the type may seem to prove that the rifle is 

 inaccurate or improperly sighted when it is not, and we can not 

 assume that because a type shows the influence of aim it is a 

 test of aim. 



So a characteristic or a group of characteristics of living things 

 may conform to the mathematical law of deviation from a mean, 

 and may thus form a type, and this type may show the influence 

 of inheritance, without being a safe basis for generalization re- 

 garding inheritance. 



This may be illustrated by an example. If we were to tabu- 

 late the prices of all the horses sold within a given period, we 

 should undoubtedly find that they would conform to a type : that 

 there is a mean or average price ; that the horses which fetch 

 more than this price are equal in number to those which fetch 

 less, and that the prices group themselves about the mean accord- 

 ing to the law of error. If the term be long enough to include 

 several generations, we shall find that inheritance or " blood " has 

 a marked influence on price, and that the children of high or 

 moderate or low priced parents are much more likely than horses 

 selected at random to bring the same price. This type will ex- 

 hibit the influence of inheritance, but it will be of no value in 

 studying inheritance unless we can in some way separate the in- 

 fluence of blood from the influence of supply and demand which 

 has far more to do with the average price and with the type. 



That the price of horses is, on the whole, determined like that 

 of other commodities is obvious, and it is also obvious that the 

 type may be changed by events which have no relation to inher- 

 itance, such as the application of electricity to street cars. 



A change of this sort, such as took place when steam replaced 

 stage coaches, is a " sport " or sudden and fundamental change of 

 type, but this may also be changed by slight and gradual niodifi- 



VOL. XLVIII. 44 



