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Gains to cooperation drive the evolution of egalitarianism

Abstract

What conditions favour egalitarianism, that is, muted hierarchies with relatively equal distributions of resources? Here, we combine the hawk–dove and prisoner’s dilemma games to model the effects of economic defensibility, costs of competition and gains from cooperation on egalitarianism, operationalized as the absence of hawks. We show that a ‘leveller’ strategy, which punishes hawkishness in the hawk–dove game with defection in the prisoner’s dilemma, can be evolutionarily stable provided that the gains from cooperation are high relative to the benefits of hawkishness. Under these conditions, rare mutant levellers select for hawks that acquiesce to punishment by playing dove. If these ‘acquiescent hawks’ become common, levellers outperform hawks and establish a new egalitarian equilibrium. An analysis of human foraging groups corroborates these results, as groups with a greater reliance on cooperation are more egalitarian. Cooperation fosters greater equality when individuals can withhold its benefits from would-be dominant individuals.

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Fig. 1: What conditions favour the evolution of levelling?.
Fig. 2: Increased gains to cooperation allow the evolution of egalitarianism through levelling.
Fig. 3: Long-run outcomes as a function of gains to cooperation (b) after 100,000 generations.
Fig. 4: Egalitarianism increases with dependence on hunting across 337 foraging societies.
Fig. 5: The effect of the initial frequency of acquiescent hawks (left) and mutation rate m (right) on the evolution of levellers in the simulation.

Data availability

The Binford hunter-gatherer data are available at GitHub (https://github.com/benmarwick/binford or https://github.com/systemsscience/egalitarian).

Code availability

Code for the simulations and empirical analysis is available at GitHub (https://github.com/systemsscience/egalitarian).

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Acknowledgements

We thank M. Hamilton, C. Hauert, G. Wild, D. Bhat, S. Bowles, E. A. Smith, C. van Schaik and S. Gavrilets for input and feedback. P.L.H. was supported by an Omidyar Fellowship at the Santa Fe Institute.

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P.L.H. and H.S.K. conceived the research. P.L.H. developed and analysed the model. A.V.J. analysed the empirical data. P.L.H. and A.V.J. wrote the paper.

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Correspondence to Paul L. Hooper.

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Hooper, P.L., Kaplan, H.S. & Jaeggi, A.V. Gains to cooperation drive the evolution of egalitarianism. Nat Hum Behav (2021). https://doi.org/10.1038/s41562-021-01059-y

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