The coevolution of culture and environment.

We propose a model of multi level (group) selection in the presence of climate variability, where environment and culture coevolve. The model describes a population subdivided into groups, each with access to a renewable resource. Individuals employ different harvesting strategies: Defectors harvest more resources than cooperators and punishers. In groups with many defectors, resource extraction may exceed the level of sustainable harvests, causing resource exhaustion. Weather shocks accelerate resource scarcity and eliminate groups with many defectors. The model is used to study conditions under which resource conservation evolves. Conservation is costly but enhances group's chances of survival. We study conditions under which environmental crises enhance the evolution of cooperation. We examine how between-group interactions such as resource-conflict and harvest-sharing affect the probability of resource exhaustion.