  Theorists of evolution are sometimes criticized for offering ‘just so’ stories of adaptation. How a given serviceable feature might have evolved is taken as tantamount to how it actually did evolve. There is, however, a valuable insight about the nature of evolutionary science to be gleaned from the practice of giving likely stories of evolution. The general form of explanation by utility is more important than which particular explanation by natural selection is advanced to explain a feature or structure. At this very early stage of reception of Darwin's theory, Wright had already realized this. In correspondence with Darwin, Wright said, “The inquiry as to which of several real uses is the one through which natural selection has acted for the development of any faculty or organ … has for several years seemed to me a somewhat less important question than it seemed formerly and still appears to most thinkers on the subject” (L 335). Wright thought there might be a plurality of uses for the same feature in the history of an organism.  Sometimes these uses are contemporaneous; at other times they succeed one another in the course of evolution. Wright believed that thinking in terms of natural selection would shed light on physiological questions and connect chemical and physical explanations to the more complicated phenomena of life (PD 296). He realized that natural selection promised to be a research program for investigation that would unify biological science.