Sickle cell anemia is a painful and often lethal (deadly) disease. individuals with sickle cell anemia have shorter than average lifespans and have fewer than average children. and yet, despite these obvious and severe disadvantages, about four million people worldwide have it. how can a trait that directly limits an individual's evolutionary fitness (reproductive success in a particular environment) still be so common? in this lesson, you will discover the answer using your knowledge of genetics, data analysis, and evolution. what to do read "sarah's story. then, answer the analysis questions, refer to the bite in your answers when needed.