Kin form important political groups, which change in size and relative inequality with demographic shifts. Increases in the rate of population growth increase the size of kin groups but decrease their inequality and vice versa. The optimal size of kin groups may be evaluated from the marginal political product (MPP) of their members. Culture and institutions affect levels and shapes of MPP. Different optimal group sizes, from different perspectives, can be suggested for any MPP schedule. The relative dominance of competing groups is determined by their MPP schedules. Groups driven to extremes of sustainability may react in Malthusian fashion, including fission and fusion, or in Boserupian fashion, altering social technology to accommodate changes in size. The spectrum of alternatives for actors and groups, shaped by existing institutions and natural and cultural selection, is very broad. Nevertheless, selection may result in survival of particular kinds of political structures.demography ͉ selection D emographic fluctuations affect the composition of kin groups (1). Positive shocks increase numbers of kin per person but decrease inequality of kin distributions and vice versa. Kin are the main source of political support and action in the small societies that characterized Ͼ90% of human history and still predominate in many societies, including segments of larger societies. Fluctuations in the mean supply of kin and the inequality of kin distributions give political actors opportunity to consolidate their positions and to select or alter cultural institutions that give advantage. Demographically induced fluctuations in kinship distributions may have been important environmental factors in natural and institutional selection as well as in particular historical events. However, any intrinsic directionality in selection is subject to existing local institutional and environmental factors.This article presents a formal model of kinship factors, first focusing on a microeconomic analog, and then taking a broader macroeconomic and ecological perspective. It then discusses some ethnographic examples and offers conjectures on implications for the development of political institutions.
A Formal Model of Kinship PoliticsEach political actor is a member of a kin group. Each kin group can have from zero to some number of additional persons. Any member can be thought of as the principal actor in the group, or the group can be thought of as an entity. Each group is, in principle, nested, with superordinate levels at greater collaterality. The model is unilineal, agnatic, and segmentary. † Thus, a set of agnatic male second cousins may consist of more than one set of agnatic male first cousins, which may consist of more than one set of brothers. At any level, groups are assumed to be mutually exclusive; for example, Ego cannot belong to more than one set of agnatically related brothers. At any level, groups may compete for dominance, regardless of whether they are subsumed under a broader group; for example, two sets of brother...