Alien contact is perennially the most popular theme of standard science fiction—futuristic humans from Earth fly on spaceships to explore alien civilizations as in Star Trek . . .
Aliens attack, invade, or otherwise visit Earth as in Independence Day, The War of the Worlds, E.T. the Extra-Terrestrial, The Day the Earth Stood Still, and many other titles with many variations in content and genre-style. (Genre is usually romance-adventure but may also become comedic or satirical, as with Men in Black or Mars Attacks!)
Narrative conflict or adventure rises from characters—humans and aliens—encountering each other as self and other, assessing nature of exchange, followed by action, learning, resolution, sometimes with an open-ended future.
The Aesthetics (sensory and intellectual pleasures) of alien contact often involve the tension or terror of the self meeting the other and a sense of wonder or the sublime. (The sublime may always quickly turn into the ridiculous, however. See Men in Black, Mars Attacks!, or Clintons and Space Alien below.)
Protagonists / heroes: The human "space ranger" is the classic example of the science fiction protagonist as "the competent man" who can rise to any challenge, repair or improvise technology, decide quickly and shoot accurately—much like a heroic cowboy on the western frontier.
Standard pop science fiction nearly always follows formulaic romance characterization of heroic men and helplessly confused women, with the male hero's populist virtue contrasted and validated by an extraterrestrial villain, who often appears as an exotic "other" to the Anglo-American "self."
With women's equality, recent women characters become less helpless and sometimes lead missions; e.g. Ripley in the Alien series.
Antagonists / villains: In early sci-fi, if the villain was humanoid, he often appeared Oriental (e.g. Ming the Merciless in Flash Gordon; lately the villain may appear more like a cold, sneering European.
The villain may also appear non-human, usually combining insect and reptile features.
Villains may also be ghostly or satanically-tempting and deluding shape-shifters, as in Species.
Or there's always the zombie option in which aliens take over human bodies living or posthumous.
In any case, science fiction villains often share features with contemporary terrorists, particularly by behaving in "inhuman" ways such as ambushing innocent humans or eating, taking over, or otherwise desecrating human bodies.
Setting: Two dimensions prevail, with many variations between.
Alien invasion stories occur mostly on Earth, occasionally on a spaceship from Earth (as in the original Alien).
Exploration stories take place in outer space or on newly discovered planets.
Time-frame relative to narratives of the future
Exploring alien civilizations is normally deep-future; being explored is near-future and usually apocalyptic.
Alien invasion stories are typically apocalyptic, with much of the action taking place in a post-apocalyptic survival mode, though
More on evolution: Stories like "The Poplar Street Study" show aliens altering the social environment of Earth. Older people, used to old ways, cannot adapt, but younger, smart people like Sunny, who aren't as invested in previous social or environment models, more quickly see the new reality, learn from it, and adapt accordingly.
Stories like "They're Made Out of Meat" and "Hinterlands" show evolutionary-scale time-spans beyond human intelligence or conceptualization, in contrast to apocalytpic time-frames, which fit humanity's general inability to think beyond its own generation.
Alien invasion > dystopia, slavery, colonial oppression?
Humans exploring in spaceships often imitate the multicultural politics of military movies in which representatives of various ethnicities work together as a team. The original Star Trek was famous for showing the first interracial kiss on American television, a liberty granted by its deep-future setting.
If American or First-World humans are spreading civilization to other planets, as with colonialism this scenario assumes extraterrestrials have everything to learn from us and we have nothing to gain from them except resources, trade, and possible colonies.
Literary and Popular Appeals:
Apocalyptic immediacy of alien invation
Battle action, plus fewer reservations about killing aliens (esp. alien robots) than about killing other earthlings.
Sexual titillation, e. g.,
Friendly introduction to online studies of alien-contact scenarios: Christian Schoon, "Alien Contact . . . "
Discovery article: "To Save the Galaxy, Destroy Humanity!"
Aliens as comedy or humor
Weekly World News, 1979-2007
Questions raised by popularity of Alien Contact scenario
An extraterrestrial who somehow saw our television and movies might conclude that humans have abundant historical experience exploring other worlds or being visited by creatures from other planets.
In fact, however, no direct or irrefutable evidence exists that Earth has ever been visited by extraterrestrials. (Books like Erich von Daniken's Chariots of the Gods and the History Channel's Ancient Aliens say, "If you accept this premise, then this extrapolation could mean . . . ," but their premises are never anything that reputable scientists acknowledge as indisputable fact.
This situation raises two questions:
1. Why do people on earth constantly fantasize about extraterrestrial life?
2. Since compelling statistical evidence exists that life should exist elsewhere in our universe, why hasn't Earth been visited or at least received a signal from an intelligent life source somewhere, anywhere in our galaxy?
Possible answers to Quesstion 1. Why do people on earth constantly fantasize about extraterrestrial life?
Since extraterrestrial species can be imagined, their creation can become a playground of human creativity—a playground that is all the freer for their being no reality to limit creativity. However, with few exceptions nearly all exterrestrial creatures look humanoid with cosmetic differences (Klingons' wrinkles, Vulcans' pointy ears). When ET creatures are not humanoid, they often become repulsive giant insects or have undersea tentacles as in Starship Troopers or Independence Day.
Aliens correspond to ghosts but in space rather than time. Whereas ghosts are human-like intelligences from a future beyond death, aliens are a human-like intelligence from a space (not a time) beyond Earth.
Such encounters between peoples in history and fiction create case studies, scenarios, or thought experiments in self-other interactions, in which an in-group (the self) may learn about itself through interaction with a different or dehumanized "other" that may be another culture or people or, in this case, an alien intelligence or entity.
An example in popular American sf movies is the persistence of "Cowboy and Indian" or "Freedom Fighters versus Dark Empire" themes as in the Star Wars franchise. (2013 movie: Cowboys and Aliens).
Such interactions between distinct races or intelligent beings engages the dialectic of the self and other, in which the "self" or protagonist symbolizes the virtues associated with an in-group like the family, tribe, or nation, while the "other" symbolizes the alternative values that threaten the self.
The extremes of self and other can sometimes enter a realm of difference or exchange, in which the two parties trust each other enough to trade rather than fight, affirming each other's humanity and worth.
The general popularity of apocalyptic / revolutionary scenarios for narratives, as alien contact brings the potential for radical change and potential destruction of life on earth.
Answers to Question 2. Since compelling statistical evidence exists that there is or should be life elsewhere in our universe, why hasn't earth been visited, or at least received a radio signal from some intelligent life source somewhere in our galaxy?