This kind of “counterfactual history” is derided by some historians, but there’s more to it than a new parlor game for scientists (although it can be that, too). It allows us to scrutinize and maybe challenge some of the myths that we build around scientific heroes. And it helps us think about the way science works: how ideas arise out of the context of their time and the contingencies and quirks of individual scientists. ... the most obvious candidate to replace one genius seems to be another genius. No surprise, maybe, but it makes you wonder whether the much-derided “great man” view of history, which ascribes historical trajectories to the actions and decisions of individuals, might not have some validity in science. You might wonder whether there’s some selection effect here: We overlook lesser-known candidates precisely because they weren’t discoverers, even though they could have been. But it seems entirely possible that, on the contrary, greatness always emerges, if not in one direction then another.