The traditional disease model, still dominant in psychiatry, is less than ideal for making sense of psychological issues such as the effects of early childhood experiences on development. We argue that a model based on evolutionary thinking can deepen understanding and aid clinical practice by showing how behaviours, bodily responses and psychological beliefs tend to develop for ‘adaptive’ reasons, even when these ways of being might on first appearance seem pathological. Such understanding has implications for treatment. It also challenges the genetic determinist model, by showing that developmental pathways have evolved to be responsive to the physical and social environment in which the individual matures. Thought can now be given to how biological or psychological treatments – and changing a child’s environment – can foster well-being. Evolutionary thinking has major implications for how we think about psychopathology and for targeting the optimum sites, levels and timings for intervention