Contemporary Astronauts, as i understand it, can be Scientists "trained" to do the job in space... Yes? But, originally, they were all Military.. mostly Pilots, if i recall ...
As I understand it, anyone who travels above 62.1 miles in altitude is considered an "astronaut."
During the Apollo moon missions, NASA thought it would be easier and faster to train pilots to be scientists, as opposed to training scientists to be pilots. The only exception I know of is Harrison Schmitt, who received a Ph.D. in geology from Harvard University, and after being selected was trained by NASA to be a jet pilot. He flew on Apollo 17.