High frequencies of alpha-thalassaemia are the result of natural selection by malaria.
Flint J., Hill AV., Bowden DK., Oppenheimer SJ., Sill PR., Serjeantson SW., Bana-Koiri J., Bhatia K., Alpers MP., Boyce AJ.
The frequency of alpha+-thalassaemia, but not other unlinked DNA polymorphisms, exhibits an altitude- and latitude-dependent correlation with malaria endemicity throughout Melanesia, supporting the hypothesis that protection against this parasitic disease is the major factor responsible for the high frequencies of haemoglobinopathies in many parts of the world.