Much British literature of the 1890s contained pessimistic and nihilistic attitudes. Wells' The Time Machinereflects the cultural and intellectual climate of the last Victorian decade (he wrote the book in 1895), and is influenced by new discoveries in biology. Darwin's texts and T. H. Huxley's teaching showed that man's life-span is very short compared to geological time, and that man can actually be evolving downwards, like the ape-like Morlocks in the book. In 1892 Max Nordau published Degeneration,which Wells read. Degeneration was an attack on the wealthy who did not work and the kind of art that lacked moral grounding. It argued that the human species was degenerating as a result of its evolution—relying on technology, sharp class distinctions, and life without strong moral purpose. These are the ideas that influenced Wells in creating the Morlocks and Eloi. The purposeless good life of the Eloi (or wealthy upper classes and the art they produced) would eventually devolve into the Morlocks, who would, though underground and apparently “below” the Eloi, be the real class in power.
The Morlocks are believed to have developed from the working class of society. They were sent underground to operate and tend to the machines. As time passed, the Morlocks changed to adapt to their environment underground. They became smaller, extremely white-skinned, with large eyes. They're ape-like in their behavior and afraid of fire and light. They now have control over the Eloi because the Eloi depend upon them for everything in their lives. The Morlocks are carniverous and "harvest" the bodies of the Eloi for food.
The Eloi are thought to have devolved from the upper class, those who owned land. They are vegetarians and live above ground. As time passed, there was less and less work to do, so the Eloi became smaller and very frail, even though are a gentle group of beings. They are only about four feet tall and childlike in their behavior. It's ironic that they now depend upon the Morlocks for their very existence.