In H.G. Wells's novel "The Time Machine," the Eloi are one of two post-human races discovered by the Time Traveler. They have evolved from humans, as have their underground counterparts, the Morlocks.
The Eloi are beautiful and fragile. They live on the surface of the planet and do not work; instead, the Morlocks, who live underground, do all the work to provide food and infrastructure to the planet. Because the Eloi have no further need for strength or intelligence, they have evolved to become naive and rather stupid. However, the Time Traveler later learns that the Morlocks eat the Eloi, which elucidates why the Eloi fear the dark.