214 POPULAR SCIENCE MONTHLY. 



It will be noticed that the families of sizes ranging between three 

 and six, both inclusive, are tindnly few. It might be supposed that 

 this is due to the artificial limitation of families, more especially since, 

 as Karl Pearson has pointed out, in the normal families themselves 

 there is already a deficiency in those groups, probably due to this 

 cause. I am, however, inclined to doubt whether that is so in the case 

 of families of men of genius, although to some extent it may be so. 

 There seems some reason to suppose that from the present point of 

 view the group may not be homogeneous, but made up in part of men 

 with feeble vitality and a tendency to sterility, and in part of men 

 with a tendency towards unusual fecundity, thus leading to a deficiency 

 of medium-sized families. 



In the case of 147 families of men of genius, it has been possible 

 to ascertain the number of children of each sex. This is found to be 

 100 girls to nearly 103 boys. This is almost the normal proportion of 

 the sexes at birth at the present time in England. If, however, I am 

 right in supposing that in a certain proportion of our cases the biog- 

 raphers have stated not the gross fertility, but only the net fertility (or 

 the surviving children), we are not entitled to expect so close an ap- 

 proximation to the proportions at birth, since the preponderance of 

 boys begins to vanish immediately after birth. The figures thus sug- 

 gest that the families of men of genius show the same tendency to 

 excess of boys, which we have already seen to be clearly marked in 

 the case of the families producing men of genius. The data are too 

 few to indicate whether there is any corresponding excess of girls in 

 the families of women of genius. 



VII. DUEATION OF LIFE. 



IT has long been a favorite occupation of popular writers on genius 

 to estimate the ages at which famous men have died, to dilate on 

 their tendency to longevity, and to conclude, or assume, that longevity 

 is the natural result of a life devoted to intellectual avocations. The 

 average age for different groups, found by a number of different in- 

 quirers, varies between sixty-four and seventy-one years. One writer, 

 who finds this highest age for certain groups of eminent men of the 

 nineteenth century, argues that here we have a test from which there 

 is no appeal, proving the preeminence of the nineteenth century over 

 previous centuries, and its freedom from 'degeneration.' It did not 

 occur to this inquirer to ask at what age the famous men of earlier 

 centuries died. I have done so in the case of a small group of ten 

 eminent men on my list, dying between the fourth and the end of the 

 thirteenth centuries — including, I believe, nearly all those in my list 

 of whose dates we have fairly definite information during this period 

 — and I find that their average age is exactly seventy-four years. So 



