Recent discussions in the philosophy of biology have brought into question some fundamental assumptions regarding evolutionary processes, natural selection in particular. Some authors argue that natural selection is nothing but a population-level, statistical consequence of lower-level events (Matthen and Ariew [2002]; Walsh et al. [2002]). On this view, natural selection itself does not involve forces. Other authors reject this purely statistical, population-level account for an individual-level, causal account of natural selection (Bouchard and Rosenberg [2004]). I argue that each of these positions is right in one way, but wrong in another; natural selection indeed takes place at the level of populations, but it is a causal process nonetheless. 1. Introduction 2. A brief justification of population-level causality 2.1 Frequency-dependent selection 2.2 Accounts of causation 3. The montane willow leaf beetle: a causal story 4. The montane willow leaf beetle: a population-level story 4.1 Response to ‘naïve individualism’ 4.2 Response to ‘sophisticated individualism’ 5. Conclusion