Biology > The Relationship Between Sickle Cell Anemia and Malaria
Describe the relationship between sickle cell anemia and malaria. Include in your answer the role that is played by rain forest agriculture.
In my essay I will discuss how sickle cell anemia became an advantage in the sub-Saharan Africa, where the rainforest clearing increased the spread of Anopheles mosquitoes and the malaria disease.
Falciparum malaria is transmitted by the female Anopheles mosquito and it is one of the deadliest diseases. Malaria is caused by several related parasitic microorganisms that feed on red blood cells. People who produce normal red cells are good hosts and easily get the disease. Each year, malaria attacks about 400 million people. While 10% of the world’s human population has been infected by malaria, 90% of the cases are in sub-Saharan Africa.
About 2000 years ago as a result of the agricultural revolution and the human population explosion in sub-Saharan Africa the rain forest clearing was increasing. The slash-and-burn cultivation and high level of rainfall erodes the soils which are relatively impermeable, making for formation of pools of water. During the rainy season pools of fresh water form, exposed to sunlight because of the forest clearing, which along with high humidity creates an ideal breeding areas for Anopheles mosquitoes. The progressive increase in population made it easier for mosquitoes to find hosts and to spread malaria. The more people had malaria the easier it was for the mosquitoes to find a new host and spread the disease. The sickling allele became increasingly valuable as a population defense against the devastating effects of malaria.
There is a very common inherited condition known as sickle cell anemia in African malarial zones. Sickle cell anemia is caused by a "defective" allele of the gene coding for a subunit of the hemoglobin protein. The sickled red blood cells plug the blood vessels, thus preventing normal red blood cell passage and, consequently, depriving the tissue of needed oxygen.
People with normal hemoglobin are homozygous dominant and are susceptible to death from malaria. People with sickle cell disease are homozygous recessive sicklers have resistance to malaria because their misshapen red cells are poor hosts. Unfortunately they are susceptible to death from the complications of sickle cell disease. People who are heterozygous for sickle-cell trait also have moderately good resistance to malaria because some of their red cells are deflated, but they rarely develop the severe life threatening anemia. Children with one gene for normal hemoglobin and one gene for sickle hemoglobin are more likely to survive their initial acute malarial attacks, therefore the people with sickle cell trait are more likely to reach reproductive age and pass their genes on to the next generation.
In conclusion, in North America sickle cell anemia is uncommon and a disadvantage. In other parts of the world especially where malaria is common, the occurrence of sickle cell anemia is greater and an advantage. The environment ultimately selects individuals with the best suited genotypes to survive and reproduce. Those individuals who have more surviving offspring pass on more of their genes to the next generation. Those who produce more offspring have a greater influence on the gene frequencies of the next generation. This mechanism of evolutionary change was first articulated by Charles Darwin.
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