For example, the gene that causes sickle-cell anemia, which can cause severe pain in the bones, joints, and abdomen and is found predominantly in black people, also has an antimalarial effect. Scientists have therefore conjectured that in Africa, where malaria is rife, the sickle-cell gene has survived in the population as an evolutionary protection mechanism.
以會造成骨骼、關節、腹部劇烈疼痛的「鐮狀細胞貧血症」的基因為例，此一基因多半存在於黑人族群中，並同時具有抗瘧疾的作用，推測是黑人族群在疫癘橫行的非洲生存所必須的，因此才得以通過演化的考驗而留存至今。