The Yahoos are a primitive human-like race which Gulliver encounters in the land of the Houyhnhnms, just before meeting the horses themselves. Gulliver does not seem to make the connection between the Yahoos and primitive humans, as he describes them to be animals: " . . . deformed . . . . Their heads and breasts were covered with thick hair . . . but the rest of their bodies were bare . . . . They had no tails and often stood on their hind feet . . . ." He concludes with, "I never beheld in all my travels so disagreeable an animal."
Houyhnhnms live simple lives wholly devoted to reason. They speak clearly, they act justly, and they have simple laws. Each Houyhnhnm knows what is right and acts accordingly. They are untroubled by greed, politics, or lust. They live a life of cleanliness and exist in peace and serenity. They live by the grand maxim: Cultivate Reason and be totally governed by it. So perfect is their society, in fact, that they have no concept of a lie, and therefore no word to express it. The only word for evil is "Yahoo."