Primogeniture, Monogamy and Reproductive Success in a Stratified Society

This paper explores the workings of stratified societies in which there is primogeniture and where the nobility practice monogamous marriage with a double standard of sexual fidelity. The paper models a simple stratified society and defines the reproductive values of male and female nobility relative to that of commoners. It goes on to explore implications of the hypothesis that preferences have evolved to favor maximization of reproductive value. This hypothesis is tested against fragmentary data from ancient civilizations and quite detailed information about the British aristocracy in the seventeenth and eighteenth centuries. This work has been strongly influenced by theoretical discussions and empirical evidence found in the writings of an anthropologist, Laura Betzig, and an historian Lawrence Stone. Primogeniture, Monogamy and Reproductive Success in a Stratified Society Theodore C. Bergstrom According to Laura Betzig (1993), the first six great ancient civilizations for which reasonable historical records exist were Mesopotamia, Egypt, Aztec Mexico, Inca Peru, India, and China. Betzig maintains that all were highly stratified societies with extreme inequality of wealth and with extreme inequality of male reproductive success and that the wealthy nobility in each of these societies practiced monogamous marriage, but highly polygynous mating. The British aristocracy of late medieval and early modern times likewise had monogamous marriage and polygynous mating. Lawrence Stone (1965) reports that: “In England as in all other European societies, marriage gave the husband monopoly rights over the sexual services of the wife, but conferred on the wife no reciprocal monopoly over the husband. In the early sixteenth century open maintenance of a mistress–usually of lower-class origins–was perfectly compatible with a respected social position and a stable marriage. Peers clearly saw nothing shameful in their liaisons, and up to about 1560 they are often to be found leaving bequests to bastard children in their wills. In practice, if not in theory, the early-sixteenth-century nobility was a polygamous society. Although they mated polygynously, noblemen in each of these civilizations married monogamously and practiced primogeniture (Betzig, 1993). That is, they selected a single wife who was the only woman entitled to bear the nobleman’s “legitimate” offspring–potential heirs his power and fortune. If the wife should fail to bear heirs, she might be replaced by a successor, but her legitimate progeny could not be displaced by the nobleman’s “illegitimate” offspring. Not only was the greatest part of the duke’s inheritance restricted to the offspring of a single wife, but among her children inheritance was concentrated on the oldest son. In the absence of a legitimate son, inheritance was sometimes passed to the oldest legitimate daughter, sometimes to a brother or nephew and occasionally to the son of a favored concubine. Some, but not all, of the legitimate daughters would be married to the heirs of other noblemen. All of these societies successfully maintained and replicated themselves over periods of several centuries. Betzig reports that of the six early civilizations, “Each seems a local response to local conditions; none seems to have been a product of conquest or diffusion from an other civilization.” This suggests that stratified societies in which the wealthy practice monogamy, primogeniture and a sexual double standard are quite likely to arise and once arisen can be very stable. It is therefore interesting to seek the common threads in human motivation that held these structures together, so that century after century, the actors in each of these dramas continued to play out the roles assigned to them by societal institutions. This paper tests the hypothesis that in stratified societies with monogamy and primogeniture, individual actions are consistent with each actor maximizing his or her genetic influence on future generations. In the first section of the paper we lay the theoretical groundwork for testing this hypothesis; constructing a simple model of a two-class society, introducing a recursively defined notion of “reproductive value” and calculating some simple equations that specify the reproductive values of noblemen and their wives and children relative to the reproductive value of commoners. These equations are expressed in terms of demographic parameters that can in principle be estimated