Other protective red blood cell (RBC) polymorphisms have also been shown to occur at their highest frequencies in malaria endemic populations, including glucose-6-phosphatase (G6PD) deficiency, the O blood group, and variants of the gene for complement receptor 1 (CR1) (Kwiatkowski 2005; Williams 2016; Rowe et al. 1997; Opi et al. 2018). This evidence concerns the gene CR1 and malaria.