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, also, 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;[1] 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.[2] 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 probably 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 average, we obtain the following results:
| Size of family | 1 | 2 | 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 biographers 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.
