Membership within a residential group is not stable in hunter-gatherer societies, such as those of the San, Mbuti Pygmy, Hadza, Hare Indian, Inuit, Orochon, and Ainu. Do blood kin relationships among settlement dwellers fade gradually with time in hunter-gatherer societies ? Do such gradual fadings of blood kin relations have any connections with their residential stability ? These questions have not exactly been answered up to now in the hunter-gatherer studies. The purpose of this study was to measure the degree of residential stability and to investigate the connection between the residential stability time and the blood kin retationships among settlement dwellers. The study focuses on the Ainu as hunter-gatherers in the Mitsuishi district of Hokkaido, Japan, 1864-1869. The findings of the analysis can be summarized as follows:<br>So as to measure the degree of residential stability, the length of continuous durations of inhabited settlement in one location was used and is termed “settlement stability time”. When we focused on 12 settlements from 1864 to 1869, settlement stability time was within the range of 1 to 6 years (mean 4.6 years). The total number of settlements in 1864, 1865, 1868, and 1869 was 39. The blood ratio of settlements (the number of households that have parent-child and/or sibling relations with any other household within the same settlement/total number of households) was calculated for all 39 settlements. The average blood ratio of 39 settlements was 73.6%. That is, 73.6% of 248 households had some close kin relations with at least one household within each settlement. The degree of settlement stability time had no correlation with the degree of blood ratio of settlement. There was no tendency that the settlement stability time became longer, the blood ratio of settlement became lower.<br>So as to measure the degree of residential stability by household, the average length of continuous inhabited durations at the same settlement by household from 1864 to 1869 was used and is termed “household stability time”.　When we focused on 49 households that existed in all four years 1864, 1865, 1868, and 1869, the household stability times was 1.3, 2, 3, and 6 years （mean 3.4 years）.　The household stability time had no correlation with the average blood ratio of settlements that were inhabited by household members.　There was no tendency that the household stability time became longer, the blood ratio of settlement became lower.<br>Fluid residential groupings were based on two processes: the splitting process of the resident members to various settlements and the joining process from various residential groups.　The former is termed “splitting fluidity” and the latter “joining fluidity”.　The numerical value of the degree of splitting fluidity per settement was within the range of 0 to 1 （mean 0.86）.　Just the same, the numerical value of the degree of joining fluidity per settement was within the range of 0 to 1 （mean 0.83）.　The degree of settlement stability time had no correlation with the degree of splitting fluidity, with a correlation coefficient of r=0.274.　And the degree of settlement stability time had no correlation with the degree of joining fluidity, with a correlation coefficient of r=－0.014.<br>When we focused on the 11 settlements that existed at least adjacent two years of 1864, 1865, 1868, and 1869, the average fluctuation rate of the blood ratio of settlement was ±24.9%.　These large fluctuations of blood ratios of settlements occurred mainly through splitting fluidity and joining fluidity.　The blood ratios of 39 settlements were almost always over 50% in spite of their large fluctuations.　It is recognized that fluid residential groupings had the function of ensuring sustainable blood kin relationships among settlement dwellers.(View PDF for the rest of the abstract.)