Into the Jungle Ch.8

Into the Jungle Chapter 8: A Sickle-Cell Safari

1) How did Tony Allison’s early life experiences in Kenya prepare him to make the discovery of the sickle cell-malaria link? Tony Allison’s early life experiences in Kenya prepared him to make the discovery of the sickle cell-malaria link because at a young age, Tony himself caught malaria. Tony’s experience with the disease led him to change his motivation and goals towards medical school instead of becoming a naturalist or anthropologist. When it came to enrolling to college, Tony attended the University of Witwatersrand in Johannesburg, where he met Robert Boom who influenced Tony’s interest in the origins of humans. At first, Tony went on different trips in which he gained experience in archaeology and physical anthropology. However, trying to learn the origins of humans by looking at different bones didn’t seem as the best possible choice to Tony. While finishing his medical training at Oxford University, that is when Tony realized that genetics, “such as human blood groups, would provide a better approach than linguistic or cultural traits to understanding human relationships” (Carroll, 152). Before going on his expedition to Africa to test his theory, Tony visited an expert hematologist who provided him with information on different blood types but also suggested that Tony should test the different blood samples for the presence of sickle cells. Tony took this advice and applied it to the different blood samples he took, where Tony noticed that the tribes living on the coast or near Lake Victoria had a higher frequency of sickle-cell carriers than those tribes that lived in the highlands or Central Kenya. These founding’s puzzled Tony, until he had a sudden realization. Lake Victoria and the coast are in low-lying areas, where there are high levels of malaria, whereas the highlands and Central Kenya were at higher elevations where there are fewer mosquitos. This realization led Tony to make connections between sickle cells and malaria and it all started with his first hand experience with malaria.

2) What makes the sickle-cell mutation a balanced polymorphism? The sickle-cell mutation is a balanced polymorphism because the heterozygote is advantageous over both of the homozygotes. This is due to a balance between two factors in the proportion of individuals with sickle cells. These two factors are the severity of malaria, which increases the occurrence of the sickle cell gene and the elimination rate of the genes in people dying of sickle-cell anemia.

3) Why was the demonstration of human resistance to malaria important to evolutionary biology? Tony’s demonstration of human resistance to malaria is important to evolutionary biology because it proves that the agent of natural selection is still active. His discovery is also important because the degree of resistance is measurable and important in early life, there is a simple genetic basis for resistance, and Tony successfully documented the association geographically and clinically. Tony also challenged the common belief that mutations are harmful, and provided proof that mutations can indeed be beneficial in some situations. For example, the HbS mutation is helpful in the sickle cell-malaria link but is harmful under other conditions.