The average number of children of feeble-minded people seems to be frequently about one-third more than in normal families, and is sometimes much greater.
Dr. Ettie Sayer, when investigating for the London County Council the family histories of one hundred normal families and one hundred families in which mentally defective children had been found, ascertained that the families of the latter averaged 7.6 children, while in the normal families they averaged 5.
Tredgold, specially investigating 150 feeble-minded cases, found that they belonged to families in which 1269 children had been born, that is to say 7.3 per family, or, counting still-born children, 8.4. Nearly two-thirds of these abnormally large families were mentally defective, many showing a tendency to disease, pauperism, criminality, or else to early death. 32
Here, indeed, we have a counterbalancing influence, for, in the large families of the feeble-minded, there is a correspondingly large infantile mortality.
A considerable proportion of Tredgold's group of children were born dead, and a very large number died early. Eichholz, again, found that, in one group of defective families, about sixty per cent of the children died young.
That is probably an unusually high proportion, and in Eichholz's cases it seems to have been associated with very unusually large families, but the infant mortality is always very high.