Selective pressures of the malaria parasites on humans..and vice versa.
So here's a bit of info you might find interesting regarding human evolution. I am slaving right now in writing a thesis for my master's in biology....while working full time and still gathering data...so it's been busy..however, I wanted to share this bit of info in the some scientific literature that I've been reading.
The closest relative to Plasmodium falciparum (human malaria) is Plasmodium reichenowi (a chimpanzee malaria parasite). Now as you know, chimps and humans share most of their DNA. Well one invasion protein of P falciparum shares 83% homology to the P. reichenowi parasite of chimps on the amino acid level. The overall domain structure of these two proteins is extremely similar, however, there are subtle but significant differences in the receptor sites of these proteins. The red blood cell receptor that these two proteins attach to is the Glycophorin A marker. Now, Glycophorins are evolving rapidly across the primate lineage, and huma and Chimpanzee Glycophorin A differ at 11 of 64 residues. A major biochemical change in the sialic acid has occurred in the human lineage after divergence from our common ancestor with chimpanzees with the results that the sialic acids on the red blood cell surface of chmimpanzees are laragely N-glycolylneuraminic acid, where as humans red blood cells express solely the metabolic precursor of that. This may explain the slight difference in the binding domains of these two closely related parasites. It is important to note that P. falciparum cannot chimpanzee red blood cells and that P. reichenowi cannot invade human red blood cells.
One can easily speculat that human red blood cell receptors act as selective pressurs on malaria parasites and vice versa. We have seen this also with sickle cell and the evolution of Duffy-negative individuals in Africa where another human species of Plasmodium, P. vivax, uses the Duffy blood group antigen on human red blood cells to invade. Humans that are Duffy negative, do not get P. vivax malaria, and non-coincidently, only african americans that live in areas where there is a high incidence of P. vivax malaria, are found to be Duffy negative. However, they still can get P. falciparum malaria.