Working paper

Monogamy: exception or rule?

Ingela Alger


Why are some societies monogamous and others polygynous? Most theories of polygyny in-voke male heterogeneity as an explanation. Arguing that such heterogeneity depends on men’swillingness to compete against each other in the first place, I propose an evolutionary gameto model the evolution of this trait. Lack of competitiveness (and the associated monogamousunions) is shown to be compatible with evolution if male reproductive success decreases withthe number of wives. In a model where the man and his spouse(s) make fertility and child carechoices that aim at maximizing reproductive success, I show that, due to men’s involvement inchild care and female agency over her fertility, male reproductive success is decreasing in thenumber of wives under certain conditions and increasing in others. The model thus sheds lighton the variation in polygyny rates across space and time in human societies.

JEL codes

  • D13: Household Production and Intrahousehold Allocation
  • C73: Stochastic and Dynamic Games • Evolutionary Games • Repeated Games

See also

Published in

IAST working paper, n. 20-105, July 2020