Ellis says of his general conclusions resulting from this investigation: "I made some attempts to ascertain whether different kinds of genius tend to be produced by fathers who were at different periods of life. I refrained from publishing the results as I doubted whether the numbers dealt with were sufficiently large to carry any weight. It may, however, be worth while to record them, as possibly they are significant. I made four classes of men of genius: (1) Men of Religion, (2) Poets, (3) Practical Men, (4) Scientific Men and Sceptics. (It must not, of course, be supposed that in this last group all the scientific men were sceptics, or all the sceptics scientific.) The average age of the fathers at the distinguished son's birth was, in the first group, 35 years; in the second and third group, 37 years; and in the last group, 40 years. (It may be noted, however, that the youngest father of all the history of British genius, aged sixteen, produced Napier, who introduced logarithms.) "It is difficult not to believe that as regards, at all events, the two most discrepant groups, the first and last, we come upon a significant indication. It is not unreasonable to suppose that in the production of men of religion in whose activity emotion is so potent a factor, the youthful age of the father should prove favorable; while for the production of genius of a more coldly intellectual and analytic type more elderly fathers are demanded. If that should prove to be so, it would become a source of happiness to religious parents to have their children early, while irreligious parents should be advised to delay parentage. "It is scarcely necessary to remark that the age of the mothers is probably quite as influential as that of the fathers. Concerning the mothers, however, we always have less precise information. My records, so far as they go, agree with Vaerting's for German genius, in indicating that an elderly mother is more likely to produce a child of genius than a very youthful mother. There were only fifteen mothers recorded under twenty-five years of age, while thirteen were over thirty-nine years; the most important age for mothers was twenty-seven. "On all these points we certainly need controlling evidence from other countries. Thus, before we insist with Vaerting that an elderly mother is a factor in the production of genius, we may recall that even in Germany the mothers of Goethe and Nietzsche were both eighteen at their distinguished son's birth. A rule which permits of such tremendous exceptions scarcely seems to bear the strain of emphasis."