Panspermia—the idea that the life started off-planet and managed to seed the Earth—is a recurrent trope in science fiction.

(Pseudopanspermia—the idea that the building blocks of life started off-planet—is still a widely entertained hypothesis in mainstream biology. It’s frequently noted that comets and meteors ejected from Mars contain amino acids.)

Star Trek: The Next Generation uses the panspermia hypothesis to explain why all the sapient species are humanoid. It turns out that an Ancient sapient species (who totally coincidentally look a lot like the Founders from the Dominion in Deep Space 9) colonized the entire galaxy and were the forerunners of the humans, the Vulcans, the Klingons, and the Cardassians.

And Ursula K. Le Guin in her Ekumen books similarly explains that all the sapient species in the galaxy were descendants of the inhabitants of the planet Hain.

Tangentially, a FriendFeed discussion about Darmok (ST:TNG S5E2) and the limitations of the Universal Translator.

See also: - Darmok (episode) • ST:TNG S5E2 • Memory Alpha - Shaka, When the Walls Fell • 2014 Jun 18 • Ian Bogost • The Atlantic