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Although the genetic mutation that causes sickle-cell anemia often leads to early death, the gene remains relatively common among individuals of African descent. This persistence appears to contradict the notion of "survival of the fittest," which suggests that a disorder causing such severe negative evolutionary effects and low survival rates would naturally become less frequent in a population over time.

Evolutionary Paradox of the Sickle-Cell Gene

A narrative example demonstrates how the adaptiveness of the sickle-cell mutation relies on the environment. In a malaria-prevalent region, two sisters, Luwi and Sena, are exposed to malaria. Luwi, a carrier of the sickle-cell mutation, is protected and survives, while Sena, lacking the mutation, succumbs to the disease. Luwi's survival, which allows her to reproduce, highlights the mutation's high adaptiveness in her African homeland. Conversely, if Luwi lived in the United States, where malaria is rare, the mutation would be costly—offering no health benefits while causing minor health issues for her and a high probability of sickle-cell disease in her descendants.

Example of Survival Advantage for Sickle-Cell Carriers

To account for genetic diversity and increase diagnostic accuracy, it is suggested to distinguish between a patient's ancestry and their race. Focusing on an individual's ancestry, rather than relying on racial categories, facilitates a greater and more accurate understanding of human genetic diversity.

Ancestry Versus Race in Human Genetics

A specific gene variant, which causes a serious blood disorder when two copies are inherited, is found at a significantly higher frequency in populations with ancestry from malaria-prone regions, such as West and Central Africa. Which statement best analyzes the evolutionary reason for the persistence of this otherwise harmful gene variant in these populations?

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