What is the theme in Science Fiction and Fantasy Literature by ?

Science and the supernatural. Science Fiction often reflects the time in which it is written. So it is that in the early twentieth century, when society was still heavily focused on technological innovation through science and industry, stories were often exploratory in nature. These stories were usually dominated by natural sciences like physics and astronomy, which often manifested themselves plot devices like spaceships or evolution. These plot devices were often incorporated into tales about humanity's future or alien races on other worlds. In the more metaphysical 1960s, however, books like Heinlein's Stranger in a Strange Land experimented with pseudosciences (theories or practices considered to be without scientific foundation). A good example is when Heinlein's Stranger in a Strange Land protagonist, a human given paranormal abilities by the Martians, is first asked to demonstrate his telekinetic powers: "'Mike, will you please, without touching it, lift that ash tray a foot above the desk?' . . . The ash tray raised, floated above the desk."