Falciparum (the bad kind) only crossed into humans 5000 years ago (historical time!). But it used to be worse, before the evolution of sickle cell and other defenses (O+ Duffy negative blood, I think). Vivax crossed into humans 35 kya and was probably as bad or worse than falciparum before it evolved to be less virulent.
this was an unhelpful comment, removed and replaced by this comment
Falciparum (the bad kind) only crossed into humans 5000 years ago (historical time!). But it used to be worse, before the evolution of sickle cell and other defenses (O+ Duffy negative blood, I think). Vivax crossed into humans 35 kya and was probably as bad or worse than falciparum before it evolved to be less virulent.