What two species inhabit Houyhnhnms Land according to the text?

In "Gulliver's Travels," the land of the Houyhnhnms is characterized by the presence of two distinct species: the noble Houyhnhnms, who are intelligent, rational horses living in a society based on reason and virtue, and the Yahoos, who are savage, human-like creatures that embody the worst aspects of humanity. This stark contrast serves as a vehicle for Jonathan Swift's commentary on human nature and society.

The Houyhnhnms represent an ideal of rationality and calm demeanor, while the Yahoos symbolize the basest instincts and moral degradation found in humans. Swift utilizes these two species to provoke thought about the qualities that define humanity and the various ways in which human behavior can fall short of nobility and reason. This relationship and contrast are central to the themes of the narrative, making the identification of these two species as essential to understanding the social critique present in the text.