With long tails, grasping hands and cheeky expressions, monkeys entertain and fascinate humans. But their fast reactions and smart thinking aren’t just for fun – they evolved for life in the treetops, where they live in complex social groups. Like other members of the “primate” order, which includes lemurs and slow lorises as well as monkeys and apes, they have long arms for swinging between trees, wide-eyed vision to spot food among the foliage, and large brains for forming bonds and problem-solving.
Many species of monkey are forest dwellers, and they often spend most of their time on the trees (arboreal). Others, such as the mandrill and baboons, live in savannas or rocky hillsides; they have the ability to climb but tend to stay on the ground for most of the day. Some monkeys, such as the pygmy marmoset Cebuella pygmaea, weigh about the same as an orange and are so small that they can fit in your palm!
In addition to their long limbs and gripping hands, most monkeys have prehensile tails for grasping branches. They also have a covering of hair on the majority of their bodies, with bare patches of skin around their face and buttocks. Some Old World monkeys, such as macaques, have specialized rumps that act as sitting pads; others, such as the owl monkey, are active at night.
Most monkeys communicate with one another using vocalizations, including calls, shrieks, and even grunts. They have a range of different alarms to warn fellow troops and humans of danger, such as the deep howling of the mandrill, or the quick running of the patas monkey. Some, such as baboons and drill monkeys, have doglike faces with snouts sticking out. Others, such as pygmy marmosets and cotton-topped tamarins, have grinning faces that may be seen as threats or signs of aggression.