The adaptive advantage of the sickle-cell mutation is contingent upon the geographic environment. In areas where malaria is widespread, like parts of Africa, possessing a single copy of the sickle-cell mutation is beneficial because it protects the carrier from malaria. Conversely, in regions where malaria is scarce, such as the United States, the sickle-cell gene provides no health benefits. In these environments, the mutation is a liability: carriers with one gene copy may suffer minor health issues, and those with two copies face a severe disease with no offsetting benefits.