In the distant past the Preservers transplanted endangered humanoid cultures to other worlds, which may explain the many human-like societies found far from Earth.
The Preservers were an ancient and advanced race that, according to Spock's theory, rescued primitive peoples threatened with extinction and resettled them on suitable planets. In 2268 the Enterprise found descendants of several Native American peoples on a distant world, protected by an obelisk the Preservers had built to deflect asteroids.
Kirk lost his memory there and lived among the inhabitants as Kirok, marrying Miramanee, while Spock worked to decipher the obelisk's symbols. The Preservers left little trace of themselves, and their identity remains a mystery.