The striking example that you gave is more striking than that. Having one allele actually brings protection from malaria. So the recessive is selected for..as

The striking example that you gave is more striking than that. Having one allele actually brings protection from malaria. So the recessive is selected for..as long as not too many people have it. That is why sickle-cell anemia mostly shows up in people whose ancestors came from places with a long history of malaria.