INTRODUCTION

In studying monogamy versus polygyny in humans, one can consider the diversity of marital and mating arrangements within societies or between societies. This chapter will focus on the diversity that occurs within a society, by asking two empirical questions: (i) what predicts who is monogamously or polygynously married for both males and females? and (ii) what are the consequences of both marriage types for reproductive success? Data are not available on extra-pair copulations (EPCs) or on genetic paternity in the study population. Therefore, throughout this chapter, the terms ‘monogamy’ and ‘polygyny’ refer to the number of concurrent spouses. This usage for the term ‘monogamy’ is akin to ‘social monogamy’, or ‘pair living’ as described in species for which actual mating behaviour has not been quantified.

The study of socially monogamous partnerships in a population that has both monogamous and polygynous unions helps to control for the cultural and historical complexity that obscures cross-cultural comparisons. In essence, a society with both monogamy and polygyny provides anatural experiment since these two types of union can be contrasted while holding constant a wide array of confounding variables. As demonstrated in this volume, much has already been learned about the occurrence of monogamy from parallel examples of intraspecific variation in other species. Ideally, this variation permits monogamy to be linked to relevant socioecological causes while holding phylogeny constant.

Attempts to explain the evolution of monogamy are often predicated on the assumption that monogamy is a trait that has been favourably selected. However, in humans and many other species, monogamy and polygyny are expressions of phenotypic plasticity (Vehren camp & Bradbury, 1984).