[general_re]

Carrying isn't a guarantee of survival either, but your odds are greatly improved:

"Protective effects of the sickle cell gene against malaria morbidity and mortality."

[AndrewC]

Carrying isn't a guarantee of survival either, but your odds are greatly improved:

Improved between the ages of 2 months to 16 months. But look at the HbSS and that goes on from here to eternity.

[shubi]

This graph shows that a small difference in survival percentage pressures large differences in allele frequences.