Greater wealth inequality, less polygyny: rethinking the polygyny threshold model

Cody T Ross; Monique Borgerhoff Mulder; Seung-Yun Oh; Samuel Bowles; Bret Beheim; John Bunce; Mark Caudell; Gregory Clark; Heidi Colleran; Carmen Cortez; Patricia Draper; Russell D Greaves; Michael Gurven; Thomas Headland; Janet Headland; Kim Hill; Barry Hewlett; Hillard S Kaplan; Jeremy Koster; Karen Kramer; Frank Marlowe; Richard McElreath; David Nolin; Marsha Quinlan; Robert Quinlan; Caissa Revilla-Minaya; Brooke Scelza; Ryan Schacht; Mary Shenk; Ray Uehara; Eckart Voland; Kai Willführ; Bruce Winterhalder; John Ziker

doi:10.1098/rsif.2018.0035

Greater wealth inequality, less polygyny: rethinking the polygyny threshold model

J R Soc Interface. 2018 Jul;15(144):20180035. doi: 10.1098/rsif.2018.0035.

Authors

Cody T Ross^{1

2}, Monique Borgerhoff Mulder³, Seung-Yun Oh⁴, Samuel Bowles⁵, Bret Beheim², John Bunce², Mark Caudell⁶, Gregory Clark³, Heidi Colleran⁷, Carmen Cortez³, Patricia Draper⁸, Russell D Greaves⁹, Michael Gurven¹⁰, Thomas Headland¹¹, Janet Headland¹¹, Kim Hill¹², Barry Hewlett¹³, Hillard S Kaplan¹⁴, Jeremy Koster¹⁵, Karen Kramer⁹, Frank Marlowe¹⁶, Richard McElreath², David Nolin¹⁷, Marsha Quinlan¹³, Robert Quinlan¹³, Caissa Revilla-Minaya¹⁸, Brooke Scelza¹⁹, Ryan Schacht⁹, Mary Shenk¹⁷, Ray Uehara¹¹, Eckart Voland²⁰, Kai Willführ²¹, Bruce Winterhalder³, John Ziker²²

Affiliations

¹ Behavioral Sciences Program, Santa Fe Institute, Santa Fe, NM, USA cody_ross@eva.mpg.de.
² Department of Human Behavior, Ecology and Culture, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
³ Department of Anthropology, University of California, Davis, CA, USA.
⁴ Korea Insurance Research Institute, Yeongdeungpo-gu, Republic of Korea.
⁵ Behavioral Sciences Program, Santa Fe Institute, Santa Fe, NM, USA.
⁶ Allen School for Global Animal Health, Washington State University, Pullman, WA, USA.
⁷ Dept. of Linguistic and Cultural Evolution, Max Planck Institute for the Science of Human History, Leipzig, Germany.
⁸ Department of Anthropology, University of Nebraska, Lincoln, NE, USA.
⁹ Department of Anthropology, University of Utah, Logan, UT, USA.
¹⁰ Department of Anthropology, University of California, Santa Barbara, CA, USA.
¹¹ SIL International, Dallas, TX, USA.
¹² School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA.
¹³ Department of Anthropology, Washington State University, Vancouver, WA, USA.
¹⁴ Department of Anthropology, University of New Mexico, Albuquerque, NM, USA.
¹⁵ Department of Anthropology, University of Cincinnati, Cincinnati, OH, USA.
¹⁶ Department of Biological Anthropology, University of Cambridge, UK.
¹⁷ Department of Anthropology, Pennsylvania State University, Philadelphia, PA, USA.
¹⁸ Department of Anthropology, Vanderbilt University, Nashville, TN, USA.
¹⁹ Department of Anthropology, University of California, Los Angeles, CA, USA.
²⁰ Institut für Philosophie der Universität Giessen, Giessen, Germany.
²¹ Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
²² Department of Anthropology, Boise State University, Boise, ID, USA.

Abstract

Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

Keywords: behavioural ecology; evolutionary anthropology; marriage systems; monogamy; polygyny; wealth inequality.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Female
Humans
Male
Marriage*
Models, Theoretical*
Socioeconomic Factors*