Scientists, both biologists and those in related fields, might also be part of the intended audience. They can gain insights into Darwin's thought process, how he conducted his research, and how he overcame the challenges in his time. This could inspire current scientific research and help in the development of new ideas in the field of evolution and related areas.
Perhaps the intended audience is the general public interested in science and the story of great scientific minds. Darwin's story is so fundamental to our understanding of life that many people would be interested in hearing it from his perspective.