How is it that sickle cell anemia formed because of malaria?

I think: You are asking what is the relationship between sickle cell anemia and malaria. People with sickle cell trait are somewhat protected against certain infections with malaria. This survival advantage allows for the propagation of the sickle cell gene to the offspring, and if the offspring have a survival advantage over those without the gene, they will have the opportunity to continue propagate.

Natural selection : Sickle cell trait is thought to make someone more resistant to some forms of malaria than someone with HGB aa genotype. The gene mutation occurred spontaneously in the past. Protection against malaria led to preservation of the mutation in areas with malaria. See attached link for more details. http://www.sciencedaily.com/releases/2011/04/110428123931.htm.

Genetic Selection: Evolution. The sickle cell trait is adaptive when a red blood cell is infected with malaria.