This chapter outlines the development of the theory of natural selection and the events surrounding the publication and reviewing of Darwin’s Origin of Species, especially in non-specialist publications. The different responses in Britain and the United States are noted. The role of supporters such as T. H. Huxley in reaching a popular audience is explored, although their reservations about the adequacy of the theory are also taken into account. Conservative efforts to present evolution as the unfolding of a divine plan provided a very different way of understanding the general idea of evolution. Many popular accounts failed to understand the difference between Darwin’s ‘tree of life’ model and older ideas of a linear ascent toward humanity, especially when dealing with the issue of human origins. In this area, popular interest in the gorilla as a potential ancestral form distracted attention from some aspects of Darwin’s model, as shown in more detail in Chapter 3. The early evolutionism of Herbert Spencer is introduced and his relationship to Darwinism explained.