In the Time Machine, society one million years in the future has evolved into two separate species called Morlocks and Eloi. The Morlocks represent the ugly dirty producers who by this future age, all live under ground and run the world’s manufacturing. The Eloi are the effect of the inbreeding of the elite, who by this time are simple-minded, Aryan, above-ground dwellers living in idleness and consuming only what the Morlocks produce. What was the trade off?
The Morlocks periodically rise above ground in hunting parties to kidnap and eat unsuspecting Eloi in this symbiotically vicious circle of life.