[Footnote 66: Darwin, see _Jour. Stat. Soc._, p. 173.]
[Footnote 67: Huth, _Marriage of Near Kin_, pp. 210-211.]
The earlier American writers, Drs. Howe and Bemiss, believed that consanguinity was a cause of idiocy. Dr. Howe inquired into the parentage of 359 idiots and found that in 17 families the parents were nearly related; in one of these cases there were 5 idiotic children; in 5 families there were 4 idiots each; in 3 families 3 each; in 2 families 2 each; and in 6 families i each. In all 17 families there were 95 children of whom 44 were idiots, 12 were scrofulous and puny, 1 was deaf, 1 dwarf--58 in low health or defective, and only 37 fairly healthy. These of course are selected cases and do not indicate at all, as Dr. Howe supposed, that consanguinity was the cause of the disasters. He adds that in each case one or both of the parents were either intemperate or scrofulous, and that there were also other predisposing causes.[70] Dr. Bemiss found that 7.8 per cent of his 3942 children of consanguineous marriages were idiots, while but 0.7 per cent of the children of non-consanguineous parentage were idiotic.[71] A more detailed examination reveals the fact that in a large number of these, one or both of the parents were mentally defective. For example, in a marriage of double cousins the wife was "feeble minded" and the six children were of inferior mentality. In a case of first-cousin marriage the wife became insane and two of the children were idiotic. In a case of the marriage of cousins, themselves the offspring of cousins the husband was a hypochondriac, and seven children idiotic. In another marriage of the same class both parents were feeble-minded and the children idiotic. These are simply taken at random, and many others might be given. When we find also that in a majority of cases no report is given of the ancestry, it is very obvious that consanguinity alone could not have been the cause of any large proportion of the 308 cases of idiocy in the Bemiss report.
My own investigations show that out of 600 children of first cousin marriage (from correspondence) 26 or 4.3 per cent are mentally defective--10 are reported as "idiots," 13 as "weak-minded" and 3 as "imbeciles." In at least five of these cases there is evidence of bad heredity, in two others the father was intemperate and in two more causes acting after birth are mentioned.