Before revision: Chimpanzees, gorillas, and humans, when walking, walk upright, and their limbs swing in opposition to one another for balance (unlike monkeys, apes lack a tail to use for balance).
After revision: orangutansChimpanzees, gorillas, and humans, when walking, walk upright, and their limbs swing in opposition to one another for balance (unlike monkeys, apes lack a tail to use for balance).