Absent Aliens/Playing With

Basic Trope: Humans are the only intelligent form of life.
 * Straight: In a Space Opera setting, humans have explored far into the galaxy and discovered no intelligent life.
 * Exaggerated: They can't even find single-celled organisms, despite sending probes to every habitable planet. Life itself only ever evolved on one planet, Earth.
 * Downplayed: Alien life has evolved to the level of animals at most, but is non-sapient.
 * Justified:
 * Human space travel is in its infancy, and we haven't had time to find them yet.
 * The odds of contacting intelligent life forms are so low that, even if they are there, it might take a million years to find one.
 * Inverted: The universe is full of aliens, but humans don't exist.
 * Subverted: Humans finally discover an alien civilization, and quickly make First Contact.
 * Double Subverted: The 'alien civilization' was actually a long lost human colony.
 * Zig Zagged: The starship Lazarus searches 1000 earth-like planets for intelligent life. Some of them offer false leads, but all of them are uninhabited. That is until the last planet they look actually does support an alien species, but it is non-sapient. However they find out the intelligent aliens were posing as non-sapient to see how the humans would treat them. Then it turns out that they are actually highly evolved humans, and the starship's crew had experienced 50 million years worth of Time Dilation.
 * Parodied: Repeated radio signals of "Hello, we come in peace." from a specific point in the sky turn out to be random noise. The cosmic background radiation just happened to make that pattern.
 * Averted: There are plenty of aliens in the universe.
 * Enforced: Aliens are avoided to save on a show's budget.
 * Lampshaded: "Don't be ridiculous, Bob. There's no way we'll find aliens on this mission."
 * Invoked:
 * Humans wanted a universe without aliens, so we killed them all.
 * We know they're there, but avoid making contact with them.
 * Exploited: If every planet is uninhabited, then we shouldn't feel too guilty about taking over the universe.
 * Defied: A scientist, bored of his own species, creates alien life in the lab.
 * Discussed: "It's strange to think that we really are alone in the universe."
 * Conversed: "It's refreshing to see a sci-fi show without those low budget aliens."

Go back to Absent Aliens if you like, but you won't find any intelligent life there.