Evolutionary processes such as natural selection and random drift are commonly regarded as causes of population-level change. We respond to a recent challenge that drift and selection are best understood as statistical trends, not causes. Our reply appeals to manipulation as a strategy for uncovering causal relations: if an appropriately controlled manipulation of variable A results in a systematic change in variable B, then A is a cause of B. We argue that selection and drift can be manipulated to produce different kinds of population-level change. They should therefore be regarded as causes.

We discuss the scientific task of historical reconstruction and the problem of epistemic access. We argue that strong epistemic support for historical claims consists in the consilience of multiple independent lines of evidence, and analyze the impact hypothesis for the End-Cretaceous mass extinction to illustrate the accrual of epistemic support. Although there are elements of the impact hypothesis that enjoy strong epistemic support, the general conditions for this are strict, and help to clarify the difficulties associated with reconstructing the deep past.

The presence of apparently irrational fair play in the ultimatum game remains a focal point for studies in the evolution of social behaviour. We investigate the role of negative assortment in the evolution of fair play in the ultimatum game. Spite—social behaviour that inflicts harm with no direct benefit to the actor—can evolve when it is disproportionally directed at individuals playing different strategies. The introduction of negative assortment alters the dynamics in a way that increases the chance fairness evolves, but at a cost: spite also evolves. Fairness is usually linked to cooperation and prosocial behaviour, but this study shows that it may have evolutionary links to harmful antisocial behaviour.

* Correspondence and requests for materials should be addressed to r.smead@neu.edu. We would like to thank the editors at Nature Climate Change as well as two anonymous reviewers for helpful comments on a previous draft of this manuscript. RLS and RS oversaw the project. RS and PF developed the models and ran simulations. RLS and JB analyzed the status of current climate negotiations and policy. RLS, RS, PF, and JB jointly developed how to apply the model to climate negotiations, derived general recommendations, and wrote the paper.

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