Figure 1.

The world distribution of haemoglobinopathies overlaps the geographic distribution of malaria. The prevalence has increased in previously non-endemic areas as a consequence of historical and recent immigration flows, slave-trade, trading activities and colonization. In all these regions there is a high prevalence of a thalassaemia. It is believed that carriers of α thalassaemia are protected against malaria and that natural selection is responsible for elevating and maintaining their gene frequencies.