It will be noticed that the families of sizes ranging between three and six, both inclusive, are unduly 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 biographers have stated not the gross fertility, but only the net fertility (or the surviving children), we are not entitled to expect so close an approximation to the proportions at birth, since the preponderance of boys begins to vanish immediately after birth. The figures thus suggest 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. DURATION 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 inquirers, 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
