When the Time Traveller discovers the existence of the Morlocks, he believes that humanity has evolved into two distinct life forms after aeons of having two castes of humans: the haves and the have nots. The Morlocks, as the laboures in this scenario, have been distanced and kept separate from the Eloi, who he thinks are the aristocracy. The "widening gulf" that exists between the haves and the have nots, which the Time Traveller can find a disturbing parallel with in his own world, would have widened ever further as culture and customs keep them separate, until eventually you have two different species evolving:
So, in the end, above ground you must have the Haves, pursuing pleasure and comfort and beauty, and below ground the Have-nots, the workers getting continually adapted to the conditions of their labour.
The Time Traveller concludes that the Have-nots would then have to pay some sort of rent to the Haves as they would be in bondage to the Haves. It is of course in this that he is disturbingly mistaken, as the rest of the novel goes on to show and as he learns more about the Morlocks.