On an Eugenic Index of Inbreeding of Farmer's Villages in Japan

Abstract

The senior author, (K.H.) has proposed an Index of Inbreeding representing the probability of producing a homozygous manifest offspring of simple Mendelian recesrsive morbid traits from consanguinous marriages within a population:
where m_n represents the number of consangUinous marriages of nth, degree and N the total number of the marriages in the population. Expressed in a unit of cousin mariage, this becomes, provided n is not smaller than 4
From a village in Okayama Prefecture, the authors record the following number of consanguinous marriages, both parties of which are living.
Degree of consanguinity: 4 5 6 7
Number of families: 50 10 6 4
among 373 families (See Table 1 on p. 17)
Hence I=0.00963
I' =0.1541
which means 15.41% of the total families correspond to the consanguity of cousin marriage, a rate veiy high compared to that of Western Countries. Percentage of cousin marriages has not shown any positive, sign of decrease since 1930 up to date, retaining a rate at about 13 or 14%
This place is the home village of the junior author, where his father has a medical dispensary and everybody knows everybody. There are no marriages more sanguinous than 4 th, degree.
The high rate of consanguinous marriages does not seem to be peculiar to this village, but rather a common phenomenon among some of Japanese farmer's villages.