On its face, a comparison of monkeys and apes seems straightforward: Modern primates have defining physical features and behaviors that clearly sort them in different categories.
Beginning with living animals, those differences are easy to pick out. Most monkeys have tails; some have prehensile tails, which means they can grasp and hold things. They're quadrupeds, meaning they use all four limbs to get around. They have four limbs that are about the same length, as well as a flexible spine.
