Explain the significance of Gulliver's fourth voyage in Gulliver's Travels

After his ship is taken over by pirates, Gulliver ends up in the land of the Houyhnhnms. It is in this place that he meets the species that is the most skeptical of him-and for good reason. Gulliver does everything he can to separate himself from the Yahoos, to separate himself from his own species. In this section, Swift accentuates the most awful characteristics of human nature.