This evidence is provided by human genetic variants conferring resistance to different pathogens: the sickle-cell trait to malaria caused by Plasmodium falciparum [1], the absence of the Duffy blood group to malaria caused by Plasmodium vivax [2], and a variant of the C-C chemokine Receptor type 5 (CCR5) chemokine to human immunodeficiency virus (HIV) infection [3]. Here, CCR5 is linked to malaria.