In the third section, relationships among genetic traits and diseases are presented. The topic of the final section is natural selection and physiological variations. Note that sometimes population biology and evolutionary principles do not stricly apply to human populations because of artificial situations imposed by humans. Note in particular the discussion about race. In the classification of animals, the term race is no longer used.
Preferred terms are subspecies or variety.
Even this is subject to much debate. Malaria is significant as a disease due to its impact on human populations, and its implications for human genetics. It has been estimated that half of all people who have ever lived on earth have died of malaria. Details of the life cycle of the protozoan parasite that causes malaria are included in the book in order to elicit an appreciation for the intricacies of the disease and an understanding of how it is transmitted. The pertinence of malaria to human genetics can be found in the discussion of sickle-cell anemia.