598 POPULAR SCIENCE MONTHLY. 



may possibly thus have been unduly diminished. Again, the biographers 

 in a very large number of cases ignore the daughters, and from this cause 

 again their statements become valueless. In estimating the natality of 

 the families producing children of ability I have never knowingly 

 reckoned the offspring of previous or subsequent marriages; so far as 

 possible, we are only concerned with the fecundity of the two parents of 

 the eminent persons. So far as possible, <»lso, I have reckoned the 

 gross fecundity, i. e., the number of children born, not the number 

 of children surviving; in the case of a large number of eminent men 

 this gross fertility is known from the inspection of parish registers; in a 

 certain proportion of cases it is probable, however, that we are only 

 dealing with the surviving children. On the whole, the ascertainable 

 size of the family may almost certainly be said to be under the mark. 

 It is, therefore, the more remarkable that the average size of genius- 

 producing families is found to be larger than that of normal families. 

 The average of the normal English family is at the very most 6;* the 

 average size of our genius-producing families is 7 (more exactly, 6.96). 

 In order to effect an exact comparison I have looked about for some 

 fairly comparable series of figures, and am satisfied that I have found it 

 in the results of an inquiry by Mr. F. Howard Collins concerning 4,390 

 families.! These families furnish an excellent normal standard for 

 comparison; they deal mainly with 'Anglo-Saxon' people (in England 

 and America) of the middle and upper classes; they represent, with prob- 

 ably but very slight errors of record, gross fertility; they are apparently 

 not too recent, and they betray little evidence of the artificial limitation 

 of families. The mean size of Collins's group of fertile families is 

 found by Pearson to be 4.52 children. Comparing in more detail the 

 composition of our genius-producing families with the normal aver- 

 age, we obtain the following results: 



Size of family 12 3 4 5 6 7 8 



Normal families 12.2 14.7 15.3 14.1 11.1 8.6 7.8 6.3 



Genius-producing families . 6.2 6.2 11.0 8.4 10.6 10.2 11.7 6.9 



Size of family 9 10 11 12 13 14 over 14 



Normal families 3.9 2.7 1.4 1.0 .5 .2 .1 



Genius-producing families.. 5.5 4.4 5.8 4.0 2.9 1.8 4.0 



Unless, as is scarcely probable, the mental eccentricities of bi- 

 ographers lead to very frequent selection on definite lines, it will be seen 

 that there is a very marked tendency for genius-producing families to 



* This was the average fertility of 1,700 marriages, as ascertained by Ansell, 

 Duncan, 'Sterility in Women,' p. 4. Galton found the mean of 204 marriages 4.65, 

 and Pearson the mean of 378 fertile marriages 4.70. 



+As quoted by Karl Pearson, 'The Chances of Death,' Vol. I., p. 70. In passing 

 through Mr. Pearson's mathematical hands the 4,390 emerge as 4,444, and it is on 

 this number that my percentages for normal families are based. 



