The Yahoos were the hairy brutes in Hounhnhnm land.
They were uncouth, uncivilised, and matched humans in appearance.
Swift describes them to be filthy in appearance and in habit.
They were primitive in nature and obsessed with "pretty stones", hence they would continuously dig dirt, to find them. '
They would fight at the drop of the hat, and were adept and sneaking, stealing and attacking.
Their women lacked morals, and indulged in lascivious activities.
The Yahoos hence, can be seen as a commentary on the materialism of human being and their selfish meaningless pursuits, and ideal contrast to the civilised, wise horses of Hounhnhnm land.