Are We Monogamous? A Review of the Evolution of Pair-Bonding in Humans and Its Contemporary Variation Cross-Culturally

Are We Monogamous? A Review of the Evolution of Pair-Bonding in Humans and Its Contemporary Variation Cross-Culturally. Ryan Schacht and Karen L. Kramer. Front. Ecol. Evol., July 17 2019, https://doi.org/10.3389/fevo.2019.00230

Abstract; Despite a long history of study, consensus on a human-typical mating system remains elusive. While a simple classification would be useful for cross-species comparisons, monogamous, polyandrous, and polygynous marriage systems exist across contemporary human societies. Moreover, sexual relationships occur outside of or in tandem with marriage, resulting in most societies exhibiting multiple kinds of marriage and mating relationships. Further complicating a straightforward classification of mating system are the multiple possible interpretations of biological traits typical of humans used to indicate ancestral mating patterns. While challenging to characterize, our review of the literature offers several key insights. 1) Although polygyny is socially sanctioned in most societies, monogamy is the dominant marriage-type within any one group cross-culturally. 2) Sex outside of marriage occurs across societies, yet human extra pair paternity rates are relatively low when compared to those of socially monogamous birds and mammals. 3) Though the timing of the evolution of certain anatomical characteristics is open to debate, human levels of sexual dimorphism and relative testis size point to a diverging history of sexual selection from our great ape relatives. Thus, we conclude that while there are many ethnographic examples of variation across human societies in terms of marriage patterns, extramarital affairs, the stability of relationships, and the ways in which fathers invest, the pair-bond is a ubiquitous feature of human mating relationships. This may be expressed through polygyny and/or polyandry but is most commonly observed in the form of serial monogamy.

Conclusion

Consensus on a human-typical mating system has remained elusive in the literature. Across human societies today, monogamous, polyandrous, polygynous, and short-term mating patterns are present, with most societies exhibiting multiple types of marriages and mating relationships. Further complicating a straightforward classification of mating system are the multiple possible interpretations of biological traits typical of humans used to indicate ancestral mating patterns. While challenging, our review of the literature offers several key insights. 1) Although polygyny is socially sanctioned in most societies, monogamy is the dominant marriage-type within any one group cross-culturally. 2) Sex outside of marriage occurs across societies, yet human extra pair paternity rates are relatively low when compared to those of socially monogamous birds and mammals. 3) While the timing of the evolution of certain anatomical characteristics is open to debate, human levels of sexual dimorphism and relative testis size point to a diverging history of sexual selection from our great ape relatives.

In sum, we conclude that while there are many ethnographic examples of variation across human societies in terms of mating patterns, the stability of relationships, and the ways in which fathers invest, the residential pair-bond is a ubiquitous feature of human mating relationships. This, at times, is expressed through polygyny and/or polyandry, but is most commonly observed in the form of monogamous marriage that is serial and characterized by low levels of extra-pair paternity and high levels of paternal care.