Sickle cell anemia is a recessive genetic disorder in which the body’s red blood cells assume an abnormal crescent shape inhibiting their ability to carry oxygen effectively. Natural selection continuously favours individuals that are better fitted to their environment; so it would make sense that the less favoured sickle cell gene should slowly disappear. However, in tropical regions where malaria is widespread, sickle cell anemia is still common, affecting 1-2% of the population. Moreover, as much as 40% of specific regional populations may carry one of the two alleles causing sickle cell anemia. Turns out, there is an advantage in carrying only one single sickle-cell gene: heterozygous individuals, though not immune to malaria, are more tolerant of malaria infection. If infected, they will also show less severe symptoms and the infection is less likely to be fatal. Voila the silver lining!
