Explain how evolution of sickle cell anemia occurred in the human population. Use the words natural selection, adaptation, and evolution in your response.

The sickle-cell allele is maintained through natural selection because of something called the heterozygote advantage.

Explanation:

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primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

if you listed your answers right then i believe your answer is b.