which two scientists are credited with developing the theory of evolution by natural selection?
Alfred Russel Wallace, codeveloper of the theory of evolution. The image is modified from http://www.prs.k12.nj.us/schools/phs/science_Dept/APBio/Natural_Selection.html. In 1858, Charles Darwin received a letter from Wallace, in which Darwin's as-yet-unpublished theory of evolution and adaptation was precisely detailed.