Research on animal behavior is typically organized according to a combination of two influential frameworks: Ernst Mayr’s distinction between proximate and ultimate causes, and Niko Tinbergen’s “four questions”. My aim is to debunk two common interpretive misconceptions about Mayr’s proximate–ultimate distinction and its relationship to Tinbergen’s four questions, and to offer a new interpretation that avoids both. The first misconception is that the proximate–ultimate distinction maps cleanly onto Tinbergen’s four questions, marking a boundary between Tinbergen’s evolutionary and survival value questions (...) versus developmental and mechanistic questions. The second is that Mayr’s proximate–ultimate distinction is meant to rule out the relevance of proximate causes to evolutionary explanations. I argue that neither is plausible given the text and Mayr’s philosophical aims, namely, to argue that evolutionary biology cannot be reduced to either the physical sciences or to other areas of biology. Through a reconstruction of Mayr’s anti-reductionist argument, I develop an interpretation according to which the proximate–ultimate distinction marks two ways that teleological reasoning can be naturalistically grounded in biology, corresponding to Mayr’s distinction between teleonomic and adapted systems. Mayr distinguishes reduction, which the proximate–ultimate distinction is meant to block, from analysis, through which he allows that proximate causes, causes that are neither proximate nor ultimate, and chance can all contribute to evolutionary explanations. I conclude by suggesting some ways in which the interpretation defended here reframes our understanding of Mayr’s disagreements with some evolutionary-developmental biologists. (shrink)