1 10 Life and Letters of Francis Gait on 



Fifty-seven fathers of these Fellows were themselves distinguished men. Now 

 let us start from distinguished fathers; we have seen (see our pp. 102-3) 

 that they are likely to have a higher percentage than mediocre fathers of dis- 

 tinguished sons, but the probability of a distinguished son occurring to a 

 distinguished father depends on the number of his male offspring. Hence if 

 we start by selecting distinguished men, we are likely to find that their fathers 

 had families above the average, especially if those fathers were themselves 

 distinguished. I do not think therefore that we can reach a measure of the 

 fertility of distinguished men from the number of their brothers, nor indeed 

 from the number of their fathers' brothers, if a large number (upwards of 50 °/ o ) 

 of those fathers were themselves distinguished. We require the number of 

 children of the Fellows themselves, and this has not been provided. 



The next point raised by Galton is of very considerable interest, namely 

 the relative intensity of heredity in the direct line and in the collaterals of 

 this line. I am a little puzzled to follow Galton here. In the direct line of male 

 ancestors there is only one representative in each generation, and there is no 

 necessity to divide by 1 1 the total marks obtained by each grade of ancestry 

 if we are dealing only with relative measures of noteworthiness. In the one 

 case of fa fa and me fa, the grandparents, Galton does divide by two. Yet 

 when he comes to the collateral kinsmen, he puts down the total marks gained 

 by brothers, and these number not 110 but 110 x 2 "43 brothers, and there- 

 fore it is not legitimate to compare the total marks obtained by brothers with 

 those obtained by "selves" or fathers. In the same way Galton does divide by 

 two the sum of the total marks obtained by paternal and maternal uncles, 

 but forgets that uncles are more numerous than fathers or selves! I have 

 therefore ventured to recompute Galton's Table III, adding to it one or two 

 additional items, but giving in each case the average number of marks 

 obtained by a kinsman of the given grade instead of Galton's total marks of 

 the class. The following will illustrate the method by which my average has 

 been obtained. There are four kinds of male cousins: (i) fa bro son; their 

 average number is 1 x{(d — \)/d\ x d, for there is only one father; his average 

 number of brothers = a — ^, and ijd (see our p. 107) is the probability that a 

 brother will have sons and d is the number of his sons. Accordingly (on Galton's 

 theory) d — \ is the number of male cousins that a man will have of the class 

 fa bro son; (ii) fa si son will also provide d — \ male cousins; (hi) me bro son 

 and (iv) me si son will give the same number, or the average number of total 

 male cousins is 4 (d — ^). Galton gives 2"43 as the average number of brothers 

 in the self generation and the father generation. Hence d — ^ = 2*43 and 

 d = 2"93, and therefore on Galton's theory 972 is the average number of male 

 cousins or 19*44 the average number of cousins of both sexes combined *. Now 

 the following are the total marks obtained by the cousins of 110 men, i.e. 

 2 138 '4 cousins : fa bro son, 45 ; fa si son, 25 ; me bro son, 46 ; and me si son, 

 31; total marks, 147. Average marks of a cousin: "07. 



* This seems to me rather a low average number of cousins for the individual, but I think 

 it is the number which results from supposing the population stable; probably no population 

 ought to be considered as such. 



