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Disease resistance

As the population grew, diseases like typhoid, cholera and malaria thrived. This may explain why so many people carry the sickle-cell and cystic fibrosis (CF) alleles. Both cause serious genetic conditions in people who inherit two copies. But people with just one copy of the sickle-cell allele are unaffected and are resistant to malaria. Some scientists believe that similarly, carriers of CF alleles resist cholera and typhoid.

Electron micrograph of sickled and normal red blood cells
Electron micrograph of sickled and normal red blood cells
EM Unit, Royal Free Hospital School of Medicine/Wellcome Photo Library

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