There is a misunderstanding here regarding the meaning of the word solution. As I use it in the context of this post, solution means something like a strategy. IOW, a global or overall solution to a problem. And of course, many particular solutions (let’s say a set of particular solutions) often exist within the space of a global or overall solution. The QC résistance in malaria is a case in point. Indeed, as you’ve noted, many particular solutions exist to confer QC resistance. But they all belong to the same set of solutions, to the same global or overall solution consisting at modifying the activity of the PfCRT receptor. IOW, during all the history of the fight between QC and Plasmodium falciparum, the bug has been able to find only one strategy or overall solution to resist chloroquine, a strategy moreover that does not involve the development of a new function but the modification of an existing one. Not very impressive I should say!