This chapter examines whether there is a relationship between the two kinds of texts that the author has identified: the theoretical contributions that use the economic metaphor of the growth of capital under compound interest in order to illustrate the demographic problem of the growth of a population, and the texts where Ronald Aylmer Fisher discusses human evolution and eugenics in economic terms. To illustrate the economic flavor of Fisher's treatment of evolution, the author first discusses Fisher's concept of fitness, which itself comes at the beginning of the section on the fundamental theorem of natural selection, probably the most famous passage of The Genetical Theory of Natural Selection (GTNS). Fisher's eugenic doctrine comes down to a few leitmotivs, almost all of which have a strong economic flavor. Finally, from a biological point of view, Fisher's economic analogy comes into play only when he discusses the Malthusian parameter.