The comparatively low averages of the consanguineous marriages from Bemiss may easily be accounted for by the fact that the cases were highly selected so that nearly one-third of the children were in some way defective, and the parents in many cases were far below the average in vitality. The "more distantly related" are in a still lesser degree representative of the class, since out of a greater possibility of choice a smaller number were chosen. The "non-consanguineous" were supposed to be near the average in vitality and fertility.
In Norway, according to Uchermann, the consanguineous and the non-consanguineous marriages are equally fertile, averaging 6.1 children per marriage;[49] and in a Black Forest village Tenckhoff found an average of 4.6 children to each consanguineous marriage as against 3.5 to each non-consanguineous marriage.[50] In regard to the youthful death-rate among the offspring of consanguineous marriages, comparison with non-related marriages is more feasible. I have counted in each case all those children who are known to have died under the age of twenty. This age was taken for the sake of convenience, and to include all children indefinitely specified as having "died young." The results are given in Table XIX:
TABLE XIX. ------------------------------------------------- Parentage. | No. of |No. dying | (Genealogies.) |Children.|under 20. |Per cent. ------------------------------------------------- First cousins | 672 | 113 | 16.7 Other cousins | 1417 | 211 | 14.9 Ch. of 1st cousins| 825 | 103 | 12.5 Non-consanguineous| 3184 | 370 | 11.6 ------------------------------------------------- (Correspondence.) ------------------------------------------------- First cousins | 759 | 88 | 11.6 Other marriages | 829 | 71 | 8.6 -------------------------------------------------
[Footnote 49: Feer, _Der Einfluss der Blutsverwandschaft der Eltern auf die Kinder,_ p. 12, _note_.]
If the figures in Table XIX are to be accepted at their face value, and there seems to be no good reason for not doing so in the genealogical cases at least, the youthful death-rate among the offspring of consanguineous marriages far exceeds the average. The average in the correspondence cases is undoubtedly too low, as many correspondents failed to report the deaths. From the fact that a comparatively large percentage of these were reported as defective, we should expect a higher death-rate than among the unbiased genealogical cases.