Pastoral science fiction—science fiction set in rural, bucolic, or agrarian worlds, either on Earth or on Earth-like planets, in which advanced technologies are downplayed.
Alternate history: time travel can be used as a plot device to explore parallel universes. While alternate history has its own category (see above), it often occurs in time travel stories as well.
^"Parasitism and Symbiosis". The Encyclopedia of Science Fiction. 10 January 2016.
^Guarino, Ben (19 May 2017). "Disgusting 'Alien' movie monster not as horrible as real things in nature". The Washington Post.
^Glassy, Mark C. (2005). The Biology of Science Fiction Cinema. McFarland. pp. 186 ff. ISBN 978-1-4766-0822-8.
^Moisseeff, Marika (23 January 2014). Aliens as an Invasive Reproductive Power in Science Fiction. pp. 239–257. {{cite book}}: |website= ignored (help)
^Williams, Robyn; Field, Scott (27 September 1997). "Behaviour, Evolutionary Games and .... Aliens". Australian Broadcasting Corporation. Retrieved 30 November 2017.