Adaptive principles of weight regulation: Insufficient, but perhaps necessary, for understanding obesity.

We reflect on the major issues raised by a thoughtful and diverse set of commentaries on our target article. We draw attention to the need to differentiate between ultimate and proximate explanation; the insurance hypothesis (IH) needs to be understood as an ultimate-level argument, although we welcome the various suggestions made about proximate mechanisms. Much of this response is concerned with clarifying the interrelationships between adaptationist explanations like the IH, constraint explanations, and dysfunction explanations, in understanding obesity. We also re-examine the empirical evidence base, concurring that it is equivocal and only partially supportive. Several commentators offer additional supporting evidence, whereas others propose alternative explanations for the evidence we reviewed and suggest ways that our current knowledge could be strengthened. Finally, we take the opportunity to clarify some of the assumptions and predictions of our formal model.