Individualist and multi-level perspectives on selection in structured populations

Recent years have seen a renewed debate over the importance of group selection, especially as it relates to the evolution of altruism. One feature of this debate has been disagreement over which kinds of processes should be described in terms of selection at multiple levels, within and between groups. Adapting some earlier discussions, we present a mathematical framework that can be used to explore the exact relationships between evolutionary models that do, and those that do not, explicitly recognize biological groups as fitness-bearing entities. We show a fundamental set of mathematical equivalences between these two kinds of models, one of which applies a form of multi-level selection theory and the other being a form of individualism. However, we also argue that each type of model can have heuristic advantages over the other. Indeed, it can be positively useful to engage in a kind of back-and-forth switching between two different perspectives on the evolutionary role of groups. So the position we defend is a gestalt-switching pluralism.