this distribution seems to indicate that the mothers of persons of intellectual ability are predominantly at the period of greatest vigor and complete sexual maturity when they produce their distinguished children., Notwithstanding the tendency of first-born children to show intellectual ability, none of the mothers are under 21.
It may be noted that in at lea«t 36 of the 276 cases in which we have details of the family history (or in about 13 per cent.) the mother was a second or third wife. In at least 6 cases the father was a second husband.
It would have been instructive to compare the ages of the parents and to ascertain the degree of disparity. I have only been able to do this in 34 cases. There is a marked tendency to disparity which ranges up to 49 years.[1] Whatever may be the normal amount of disparity between the ages of parents, it certainly tends to range chiefly below 4 years, but in this group only 8 cases (i. e., in the proportion of about 23 per cent.) show less disparity than 4 years; the majority range between 4 and 8 years, and as many as 8 (i. e., in the proportion of over 22 per cent.) show a greater disparity than 10 years.[2] In 6 out of the 34 cases the mother was older than the father. In a considerable proportion of cases both parents were elderly.
On the whole it would appear, so far as the evidence goes, that the fathers of our eminent persons have been predominantly middle-aged and to a marked extent elderly at the time of the distinguished child's birth; while the mothers have been predominantly at the period of greatest vigor and maturity, and to a somewhat unusual extent elderly. There has certainly been a notable deficiency of young fathers, and, still more notably, of young mothers.
Our data at this point are too few to be very decisive, but, so far as they indicate anything, they enable us once again to bring men of 'genius' into line with the other mentally abnormal classes. The late Dr. Langdon Down (who at my suggestion investigated the point some twelve years ago) found that in the case of the parents of idiots there was a disparity of more than ten years in 23 per cent, cases, almost the same proportion as we have found in the parents of persons of intellectual ability. Among criminals also inequality of age in the parents, as well as elderly age of both parents, has been found by Marro to be more common than among the normal population. Marro (in his 'Carat-
- ↑ This very exceptional case was that of the father (an eminent bishop) of Charles Leslie, the nonjuring divine. In this case the father was 79, the mother 30.
- ↑ In Hungary, as a table given by Körösi shows, if we take men at ages between 26 and 30, covering the most frequent normal age of marriage, in only 3 per cent, cases is the discrepancy of age as much as ten years. The disparity, of course, tends to increase with the man's higher age at marriage.
