The three chapters in this section were originally presented to quite different audiences. Chapter 4, on concepts of adaptation, was first presented at a 1981 workshop organized by Marjorie Grene concerning issues about Darwinian evolutionary theory; it was published in the volume that resulted from the workshop (Grene 1983). The participants were all advanced professionals in biology, history of biology, or philosophy of biology, so I do not set as much background as I do in the other chapters of this section. (Indeed, readers without prior background in evolutionary biology may wish to read Chapters 5 and 6 before Chapter 4.) Chapter 4 teases apart several concepts of adaptation and fitness deployed by Darwin and in the synthetic theory of evolution, which achieved orthodoxy around 1950. These concepts are often conflated with one another and need to be carefully separated to achieve a sharp understanding of the claims of various evolutionary theories. The analysis reveals some important substantive differences between Darwin's theory and the synthetic theory. In addition, it shows how easy it is to be misled into believing that the synthetic theory rests on a tautology – and does so by providing a careful account of exactly why survival of the fittest is not properly interpreted, tautologously, as survival of those that actually survive. It also offers some guidance in handling a number of delicate questions about the strength of the evidence for claims that particular traits are evolutionary adaptations by providing an account of requirements that must be met for the actual survival of organisms to provide evidence about the contribution (if any) that possession of particular traits makes to the fitness, adaptedness, or adaptation of the organisms that possess them.