First, he thinks that the Eloi are the sole descendents of humanity. He assumes that scientific progress continued to make life easier for humans, so much so that they lost their edge, becoming stupid and lazy. He implies that this fate is the result of communism, as if the lack of competition drove the human race to indolence. Second, after he discovers the Morlocks, he thinks that the Morlocks are the slaves of the Eloi. He still feels that the Eloi have devolved into frail creatures because their life is too easy, but he believes that the Morlocks, humanity's other descendent, have evolved into brute workers. He thinks that this is capitalism's division of labour taken to the extreme. Third, when he discovers that the Morlocks hunt and terrify the Eloi, he assumes that his second theory was once true, but that the Morlocks evolved to the point where they needed to prey on the Eloi. It is a theory of revenge of the working classes. These successive theories do not replace each other; rather, each one encompasses a broader view.
The Morlocks live below ground, in a system of tunnels. The tunnels can be entered through ventilation ducts that are scattered around the landscape. The ducts suck air inward and look like wells. Large underground engines keep the air flowing. The Morlocks seem to use the pedestal of the giant white Sphinx statue as a portal to the surface. Some Morlocks stay on the surface during the day, living in the shadow of ruins like the Palace of Green Porcelain. At night, the Morlocks emerge from below the ground to roam the surface. They hunt Eloi, which provide meat for the Morlocks' diet. The Morlocks are deeply afraid of light.