The Time Machine is pretty relevant here. "Later in the dark, he is approached menacingly by the Morlocks, ape-like troglodytes who live in darkness undergroun

The Time Machine is pretty relevant here. "Later in the dark, he is approached menacingly by the Morlocks, ape-like troglodytes who live in darkness underground and surface only at night. Exploring one of many "wells" that lead to the Morlocks' dwellings, he discovers the machinery and industry that makes the above-ground paradise of the Eloi possible. He alters his theory, speculating that the human race has evolved into two species: the leisured classes have become the ineffectual Eloi, and the downtrodden working classes have become the brutal light-fearing Morlocks."