Hidalgo's paper is a clear and powerful contribution to a topic of ongoing concern.1 It should be taken seriously by anyone who worries that there is something seriously wrong with the flow of medical expertise from the poor countries of the South to the rich countries of the North because it forces open the question of just what that wrongness is supposed to be. (I count myself among these worriers, but it is not obvious on examination exactly where the problem lies. The parenthetical question mark in the title of my own modest contribution to the debate2 was intended to indicate my uncertainty about whether I had pinned down the wrongness or would have to admit its absence; the more I wrote, the more I felt like an explorer who sets out to find the source of the Nile only to end up doubting the river's existence.)

Being unable to identify the moral problem about migration will not make the problem about poor health in the South go away, of course: and it might be that, if we are genuinely concerned to keep expertise in the South, we simply have to face up to the possibility of subsidising the wages …