Evolution and the ultimatum game, with Matthijs van Veelen, 2023, Games and Economic Behavior, 142: 570-612. (doi:10.1016/j.geb.2023.08.005)
In this paper we review, upgrade, and synthesize existing models from evolutionary game theory, all of which aim at explaining human behaviour in the ultimatum game. Our new and improved versions of Gale et al. (1995), Nowak et al (2000), and Rand et al. (2013) avoid shortcomings that the original versions have, one of which is that the results in the first and the last are driven by bias in the mutations. We also compare the predictions of these three models with the existing experimental evidence by looking at properties of the distributions of minimal acceptable offers. We find that the observed distributions do not conform to the predictions from Gale et al. (1995), Rand et al. (2013), or any other model in which there is no fitness benefit to rejecting. This does not rule out commitment-based explanations, such as Nowak et al. (2000).
(The code for our simulations and the data used in the analysis can be found here)
The evolution of morality and the role of commitment, with Matthijs van Veelen, 2021, Evolutionary Human Sciences, 1-53. (doi:10.1017/ehs.2021.36)
A considerable share of the literature on the evolution of human cooperation considers the question why we have not evolved to play the Nash equilibrium in prisoners' dilemmas or public goods games. In order to understand human morality and pro-social behaviour, we suggest it would actually be more informative to investigate why we have not evolved to play the subgame perfect Nash equilibrium in sequential games, such as the ultimatum game and the trust game. The "rationally irrational" behavior that can evolve in such games gives a much better match with actual human behaviour, including elements of morality such as honesty, responsibility, and sincerity, as well as the more hostile aspects of human nature, such as anger and vengefulness. The mechanism at work here is commitment, which does not need population structure, nor does it need interactions to be repeated. We argue that this shift in focus can not only help explain why humans have evolved to know wrong from right, but also why other animals, with similar population structures and similar rates of repetition, have not evolved similar moral sentiments. The suggestion that the evolutionary function of morality is to help us commit to otherwise irrational behaviour stems from the work of Robert Frank (1987, 1988), which has played a surprisingly modest role in the scientific debate to date.
The cancellation effect at the group level, with Matthijs van Veelen, 2020, Evolution, 74: 1246-1254. (doi:10.1111/evo.13995)
Group selection models combine selection pressure at the individual level with selection pressure at the group level. Cooperation can be costly for individuals, but beneficial for the group, and therefore, if individuals are sufficiently much assorted, and cooperators find themselves in groups with disproportionately many other cooperators, cooperation can evolve. The existing literature on group selection generally assumes that competition between groups takes place in a well-mixed population of groups, where any group competes with any other group equally intensely. Competition between groups however might very well occur locally; groups may compete more intensely with nearby than with far-away groups. We show that if competition between groups is indeed local, then the evolution of cooperation can be hindered significantly by the fact that groups with many cooperators will mostly compete against neighbouring groups that are also highly cooperative, and therefore harder to outcompete. The existing empirical method for determining how conducive a group structured population is to the evolution of cooperation also implicitly assumes global between-group competition, and therefore gives (possibly very) biased estimates.
(The code for our simulations can be found here)
Homo Moralis and regular altruists – preference evolution for when they disagree, with Christopher Graser and Matthijs van Veelen
Alger and Weibull (2013) present a model for the evolution of preferences under incomplete information and assortative matching. Their main result is that Homo Moralis – who maximizes a convex combination of her narrow self-interest and “the right thing to do” – is evolutionarily stable, if it assigns a weight on the right thing to do that is equal to the assortment parameter. We give a counterexample against their central result, and a way to repair it. We also show that the result ceases to hold if we allow for mixed equilibria or coordination on asymmetric equilibria. Allowing for mixed equilibria, we show that if there is a stable preference, it will be behaviorally equivalent to a regular altruist that puts a positive weight on the payoff of the other that is equal to the assortment parameter. We also consider the cross-species empirical evidence.
The evolution of honesty by partner choice, with Stephan Jagau, Shaul Shalvi and Matthijs van Veelen
Normative versus prosocial underpinnings of human decision making, with Sarah Mathew