A common science fiction topic is some sort of interaction with an intelligent extraterrestrial species at least the equal of humanity.

However, before true aliens could exist in the minds of science fiction writers, two developments had to occur:

• Astronomers had to demonstrate the existence of other planets where aliens could live;
• Darwin had to develop his theory of evolution so writers could perceive that different environments required different kinds of beings.

As demonstrated by H.G. Wells in War of the Worlds, contact with aliens often leads directly to warfare. However, the more mature alien encounter stories surmise that a contact with an alien civilization will force the Earth to look at itself differently forever after. In fact, many authors use their depiction of human interaction with aliens to comment on contemporary human behavior and events.

There are many ways to categorize stories of alien encounter.

• In some of these stories aliens come to Earth; in others humans travel to alien planets.
• In some of these stories the encounters are peaceful; in others either we or the aliens are aggressors and invaders.
• In some of these stories the encounters are public; in others, aliens attempt to keep their existence secret from all or most of the population.

A major Alien Encounter story is the First Contact story. In such a story humans and aliens meet for the first time.

Another major type of Alien Encounter story is Alien Invasion, a story that tells of an alien force coming to Earth to conquer the planet. The prototype alien invasion novel is The War of the Worlds by H. G. Wells.

There are many subsets of alien encounter stories:

• One subset of alien encounter stories focuses on religious belief and the question of whether Christ is the savior of alien civilizations as well as humans.
• Another subset of alien encounter stories focuses primarily on the difficulty of communicating with aliens.
• Interspecies mating is still another subject that is explored in such stories.

First Contact:

• Childhood's End by Arthur C. Clarke
• Close Encounters of the Third Kind (film)
• E.T., the Extraterrestrial (film)
• "First Contact" by Murray Leinster
• "A Martian Odyssey" by Stanley G. Weinbaum
• "The Sentinel" by Arthur C. Clarke, basis for film 2001: A Space Odyssey

Alien Invasion

• Independence Day (film)
• Invasion of the Body Snatchers (film)

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