Extinction was a term for the condition of a species of which there were no longer any living members.
Extinctions have occurred naturally on many worlds through the course of evolution or natural catastrophes. Some species have become extinct through artificial means such as hunting or pollution. Even intelligent species that created vast galactic civilizations were thought to have gone extinct in the galaxy's long history.
Several ancient civilizations founders were thought to have gone extinct, notably:
- - The Iconian Empire circa 200,000 years ago (TNG episode: "Contagion")
- - The Tkon Empire circa 600,000 years ago (TNG episode: "The Last Outpost")
- - The Chodak Empire circa 900,000 years ago (TNG video game: A Final Unity)
In some cases, modern descendants of ancient species may unknowingly survive as a primitive offshoot, unaware of their origins as a colony. Spock speculated that Vulcan civilization might be descended from an older ancestor species such as Sargon's race, the Arretians. (TOS episode: "Return to Tomorrow")