Monkeys: biology, classification, behavior and human connections

Classification and major groups

In common usage "monkey" covers two main evolutionary lineages. The Old World monkeys (family Cercopithecidae, commonly referenced as Old World monkeys) are native to Africa and Asia. The New World monkeys (often termed New World monkeys, including the platyrrhines) occur in Central and South America. Both groups belong to the simian infraorder alongside apes; modern apes are closely related to Old World monkeys, sharing a common ancestor rather than being direct descendants (apes and other catarrhines).

Physical characteristics

Monkeys range from very small species such as the pygmy marmoset to large species like the mandrill. Typical features include forward-facing eyes, grasping hands and nails instead of claws, and limbs suited for climbing or leaping. New World species often have prehensile tails that act as a true fifth limb, whereas Old World monkeys generally have non-prehensile tails or none in apes. Tail presence and form are important traits for distinguishing groups.

Habitat, distribution and diet

Monkeys occupy a variety of habitats from tropical rainforests to savannas and montane forests. New World monkeys are largely restricted to the Americas and are absent from the Old World: they are not native to Australia or New Guinea. Old World monkeys are mainly found across Africa and Asia. Diets are equally diverse: many species are primarily frugivorous, others eat leaves, seeds, insects or a mix of foods. Some species forage in groups and use complex vocal and visual communication to coordinate movements.

Behavior, social structure and examples

Monkeys are typically social and live in groups often called troops or tribes. Group size and organization vary widely between species; some form large, multi-male societies while others live in small family units. Examples include macaques, baboons, guenons and small-bodied monkeys such as marmosets. Many species climb and leap between trees, using long limbs and prehensile tails when present. Human beings (man) have long observed and depicted monkey behaviour in art, folklore and science.

Size extremes and notable species

• Smallest: the pygmy marmoset, native to rainforest canopies in countries such as Brazil, Colombia and Ecuador, measures only a few centimetres of body length and weighs a few hundred grams.
• Largest commonly called monkeys: species such as the mandrill can approach a metre in body length and several dozen kilograms in weight.

History, names and human uses

The English word "monkey" may trace back to medieval European tales: one suggested origin is the name Moneke in the Roman de Renart. Throughout history monkeys have appeared in religious symbolism, art and folklore. They are also used in research and sometimes kept as pets, which raises welfare and ecological concerns. In parts of the world monkeys are hunted for food—known as bushmeat—and certain practices, such as eating primate brain tissue, have been documented in regions of Africa and Asia (monkey brains).

Conservation and notable concerns

Many monkey species face threats from habitat destruction, fragmentation, hunting and capture for the wildlife trade. Conservation status varies: some species remain common and adaptable, while others are endangered or critically endangered. Conservation actions include habitat protection, legal trade controls, captive-breeding programs and community-based initiatives. Understanding species differences and distributions—from New World groups in South America to Old World forms across Africa and Asia—is essential for targeted conservation planning.

Quick reference

• Groups: Old World (Cercopithecidae) and New World (Platyrrhini/Ceboidea).
• Typical habitats: forests, woodlands and some savannas; absent from Australia and New Guinea.
• Notable species: pygmy marmoset, mandrill, macaques, baboons.

For further reading consult specialist primatology texts and reputable online resources on primate biology and conservation (arboreal behaviour, simians, comparative primate anatomy and the human relationship to non-human primates).