Biogeography teaches the reasons why this occurs by resarching species in different places in the world. Between about 1800 to 1855, natural historians made lists of species in various regions of the world. These lists were published as tables in their books. Charles Darwin and Alfred Russel Wallace published the idea of evolution by natural selection. They travelled to tropical countries to find out why species were suited to the places they lived, and wrote about the life in those countries. They said that evolution was the key to understanding geographical distribution.