29% were on biogeography and natural history, 27% were on evolutionary theory, 25% were social commentary, 12% were on Anthropology, and 7% were on spiritualism and phrenology.
29 % ze 747 kratších děl bylo o biogeografii a přírodopise, 27 % o evoluční teorii, 25 % byly společenské komentáře, 12 % bylo o antropologii a 7 % o spiritualismu a frenologii.