Individuals with the sickle-cell anemia trait are more likely to survive a malarial infection and have increased reproductive success in malaria-prone areas. This is because individuals with sickle-cell anemia
have a genetic mutation that causes their red blood cells to form a sickle shape, which makes it more difficult for the malaria parasite to infect and reproduce within the cells. As a result, individuals with the sickle-cell trait are less likely to develop severe forms of malaria and have a better chance of surviving the infection.
In malaria-prone areas, where the disease is a significant cause of mortality, individuals with the sickle-cell trait have a survival advantage. This can lead to higher rates of reproductive success, as individuals with the trait are more likely to survive and have offspring who also inherit the advantageous trait. Over time, this can lead to an increase in the frequency of the sickle-cell trait in populations living in malaria-endemic regions.
Overall, the presence of the sickle-cell trait in populations living in malaria-prone areas is an example of natural selection at work, where individuals with a beneficial genetic trait have a higher chance of survival and reproductive success, ultimately leading to evolutionary changes in the population.