Chapter 9: Disease
Chapter 9 begins by discussing the variation of blood types among humans. The discussion delves into the variation and explains it as a result of genetic mutations. Ridley differentiates between random genetic mutations and the actual mechanism of natural selection. Further into the chapter, Ridley notes how different blood types are, in truth, more susceptible to different kinds of disease. Cholera is linked to A and AB while malaria is linked to O types. Additionally, the relationship between the genetic sickle-cell disease and malaria is discussed. Ridley asserts that certain genes are still present, even if they may sometimes cause diseases, because when used in the correct combination, they code for resistance to much more deadly infectious diseases.
