Reproductive Structure of Hatomajima Population in Yaeyama Islands and its Population Genetic Analysis

Abstract

In order to study the processes developing the variation of physical traits among small human populations based on population genetics, the present investigation was carried out in the Hatomajima population of Yaeyama Islands, Okinawa.
This report is particularly concerned with demographic structure and marriage pattern, or reproductive structure, in Hatomajima hamlet and discussion was made on historical and environmental effects extending over many generations which appear to affect the development of the variation in physical traits in such a small population. The results obtained are as follows:
1) The population pattern shows advancing stages demographically, although it shows marked decrease since about 1950.
2) Gene flow seems to be very low, since endogamy rate is very high.
3) Traditionally, the tendency of avoiding the 1st cousin marriage is seen and this seems to have played a role in the effect to prevent homogeneity of physical traits in the population.
4) The average effective size of the population for the last five generations is about 50 to 60, which is rather small in comparison with other isolated populations.
5) The fluctuation of the gene frequencies found in the Hatomajima population is presumably due to the random genetic drift brought from the separation from Kuroshima population about 200 years ago.