Final answer:
The sickle cell allele's high prevalence in Africans is due to the genetic protection it offers against malaria, which increases the reproductive success of heterozygous individuals in malaria-endemic regions.
Step-by-step explanation:
The high prevalence of the sickle cell allele in Africans is largely due to its protective role against Plasmodium falciparum malaria. Heterozygotes, individuals with one normal hemoglobin gene and one sickle cell gene, are more resistant to malaria. This resistance leads to enhanced survival and reproductive success in malaria-endemic regions, keeping the sickle cell allele prevalent within the gene pool. Genetic factors, rather than environmental factors, dietary habits, or direct inheritance from ancestors, are the primary reason for this high prevalence. The fitness of individuals carrying the sickle cell allele in malaria-prone environments highlights the complex relationship between genetics and environmental factors.
It is important to note that those with two copies of the sickle cell allele (homozygous individuals) will likely suffer from the severe effects of sickle cell anemia, without the malarial protection. However, the sickle cell trait's benefits in malaria-afflicted regions maintain the allele within populations in Africa. If malaria were eliminated, the fitness advantage for carriers would disappear, potentially leading to a decrease in the frequency of the sickle cell allele over time.