Chapter 3 focuses on the process of microevolution (macroevolutionary theory is discussed in the next chapter). Biological evolution is described as genetic change through time. Building upon basic concepts introduced in Chapter 2, the chapter focuses in defining population, genotype and allele frequencies, and a brief description of the Hardy-Weinberg equilibrium. The chapter takes a relatively nonmathematical approach to microevolutionary theory, the major forces of evolution (Mutation, Natural Selection, and Genetic Drift and Gene Flow), and their effects are explained in detail. Although some specific examples from human populations are given, most case studies are reserved for later chapters.

For those wishing for a more mathematical approach, Appendix 1 (found in the Epilogue section) provides further information on basic population genetics, for which only high school algebra is required.