The different geographic distributions of sickle-cell disease, α-thalassaemia, glucose-6-phosphate dehydrogenase (G6PD) deficiency, ovalocytosis, and the Duffy-negative blood group are examples of the general principle that different populations have evolved different genetic variants to protect against malaria (see [8] for a review). This evidence concerns the gene G6PD and G6PD deficiency.