Average coefficient of relationship within troops of the Japanese monkey and other primate species with reference to the possibility of group selection

The average coefficient of relationship within troops of the Japanese monkey (Macaca fuscata) is .1667±.0433; this corresponds to anF _ST between troops of .0935±.0277. The estimate is based on polymorphic variation at 12 blood protein loci in a sample of about 1,500 individuals distributed over 33 troops. The average coefficient of relationship among adult females (the sedentary sex) is .1886±.0670 and that among adult males (immigrants) is .1067±.0382. The difference, though not statistically significant, is in the direction expected from the observed sex asymmetry in dispersal. We give an approximate formula for the coefficient of relationship between specified relatives. The coefficient of relationship in the Japanese monkey is compared with corresponding estimates in five other terrestrial primate species and in tribal man. It is suggested that the best informed guess of the average coefficient of relationship within bands of Pleistocene man may have been about 10 to 15%. This estimate is relevant to the possibility of the evolution of altruism in our ancestors by group selection.