The human genome is under continuous selective pressure for resistance to infectious diseases. Several polymorphic alleles have been associated with resistance to malaria in West African populations, for example. In the November 15 Nature, Modiano et al. report a large-scale study aimed at clarifying the role of hemoglobin C (HbC) in resistance to Plasmodium falciparum malaria (Nature 2001, 414:305-308). They evaluated allele frequencies for the β globin gene in 3,513 healthy subjects and 835 malaria patients in Burkina Faso. The results show that HbC can provide protection against P. falciparum malaria in both the heterozygous and homozygous states. The reduced risk is 93% for HbCC homozygosity and 29% for HbAC heterozygosity. The authors predict that the HbC alleles will spread across Africa, replacing the sickle hemoglobin (hemoglobin S; HbS) polymorphisms that are associated with reduced fitness.