Abstract

Theorem 1 in Alger and Weibull (Games and Economic Behavior, 2016) consists of two statements. The first establishes that Homo moralis with the right degree of morality is evolutionarily stable. The second statement is a claim about sufficient conditions for other goal functions to be evolutionarily unstable. However, the proof given for that claim presumes that all relevant sets are non-empty, while the hypothesis of the theorem does not guarantee that. We here prove instability under a stronger hypothesis that guarantees existence, and we also establish a new and closely related result. As a by-product, we also obtain an extension of Theorem 1 in Alger and Weibull (Econometrica, 2013).

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