What was the American TV show "Gilligan's Island" Professor's primary occupation?

On the "Gilligan's Island" TV show (1963–1967) the Professor's backstory identifies him as Roy Hinkley, played by John Gabriel (1963) and Russell Johnson (1964–1967), a High School Science Teacher. His principal expertise was as a botanist, whose purpose in joining the ill-fated voyage that stranded the castaways was to write a book to be titled "Fun With Ferns".

Aside from his proficiency in science, the Professor was the holder of numerous degrees from various schools (including the University of Southern California, the University of California at Los Angles, Southern Methodist University, and Texas Christian University - Fort Worth). Those degrees may just explain how he was so adept and well-versed in law, literature, social sciences, and the arts.