 There is a fundamental inferential problem in transferring what has been learned in any model (whether human, animal, or whatever) to some target population of interest has been described as the “experimenter’s circle” (Steel 2008). The problem is essentially this. What is true of a model can be presumed to be true of the target only to the extent that the model is similar to the target in relevant respects. The reason we experiment on models in the first place is, however, that the model differs in important respects from the target (if animals were just like humans, we would not find experiments on the former to be ethically less problematic than experiments on the latter). Extrapolation—the inference from model to target—is therefore only worthwhile to the extent that there are significant limitations in our ability to study the target directly. If so, there can be no good grounds to decide whether a model is a good one for the target. To do so, we would have to investigate whether the target is relevantly similar to the model; but if we could do so, there would be no reason to study the model in the first place.