Final answer:
The first carrier of the sickle cell disease gene in a region without malaria would have had the same likelihood to survive and reproduce as his peers, as the trait conveys no advantage or disadvantage without malaria. In contrast, in malaria-endemic regions, carriers have a survival advantage due to resistance to malaria, maintaining the gene's presence in the gene pool.
Step-by-step explanation:
If the mutation for the sickle cell disease gene first appeared in a region without malaria, the first carrier would have had the same likelihood to survive and reproduce as his peers. This is because in the absence of malaria, carriers of the sickle cell trait do not exhibit significant advantages or disadvantages compared to non-carriers. Outside of malaria-endemic areas, individuals with one copy of the sickle cell gene may experience minor health issues but would not have enhanced resistance to diseases that would increase their survival or reproductive success. Consequently, the sickle-cell trait would not provide a selective advantage and would likely remain a neutral trait within the population.
In stark contrast, in malaria-endemic regions, the heterozygous state (carrying one allele of the sickle cell gene) offers a survival advantage due to resistance to malaria. This advantage promotes their increased likelihood of surviving and reproducing, thereby maintaining the presence of the sickle cell trait within the gene pool. As illustrated with the example of Luwi, being a carrier of the sickle cell gene in a malaria-endemic environment like Zambia, Africa, increases an individual's fitness. Under such circumstances, the sickle cell trait works as a protective factor against malaria, which leads to a higher survival rate among carriers, hence the continued prevalence of the sickle cell gene among populations in these regions.
Conversely, individuals who are homozygous for the sickle cell gene and have full-blown sickle cell anemia do not benefit from the protection against malaria and often suffer from severe health consequences. Such individuals may have a lower survival rate and less chance to reproduce, but the continued existence of malaria supports the prevalence of the sickle cell gene in the heterozygous form. Thus, the fitness of individuals and the frequency of the sickle cell allele is heavily influenced by the presence or absence of a disease like malaria in the environment.