A monkey is a small, nonhuman primate that lives in forests or jungles. It is a member of the simiiform family, which also includes lemurs, squirrel monkeys and marmosets. Monkeys have prehensile tails that can grab and hold things, and they can use their hands to grasp branches or food. They are omnivorous, eating nuts, fruits, leaves, roots, flowers, vegetables and even the occasional bird or rodent.
Some monkeys live in groups called troops. Within these large groups, males and females live together, and the group includes infants and immature adults. Others, such as the guenon (Cercopithecus agassius) of Africa, are more monogamous and form one-male harems. Male guenons have brightly colored patches of tough skin on their rumps that they use to display dominance.
Most monkeys have cheek pouches in which they store food. Others, such as baboons, have more complicated three- or four-chambered stomachs. Those that don’t have pouches are divided into two subfamilies: cercopithecines and colobines. The cercopithecines, which include baboons and macaques, are the Old World monkeys; the colobines, including guenons and langurs, are in the New World.
Despite their close relationship to humans, most monkey species are endangered in the wild. This is because their habitat is being eroded by logging, agriculture and human settlements. They are also hunted for bushmeat and traditional medicines. For example, in Colombia, the population of Central American spider monkeys is rapidly declining because their forest homes are being cleared for cattle ranching.