The Web of Life (115) Monkeys


The term monkey may have originated from a character named Moneke in the 16th century German fable Reynard the Fox. Moneke was the son of Martin the Ape.

There has been long-standing confusion between monkeys and apes, thanks to simple-minded scientists. Into the 1950s, primate evolution was considered a Darwinian progression leading through monkeys to apes to humans. Though all primates evolved from a common ancestor 85 MYA, the evolution of humans has since been found to be considerably more complex than the straight-line descent once imagined.


Monkeys are the most colorful mammals. Their flamboyance accents their social standing. In some monkeys, such as the polygamous mandrill, the dominant male has brilliant colors, while subordinates are somewhat duller.

Monkey color vision acuity evolved to aid foraging, including the ability to discern fruit ripeness and the freshness of shoots. Once evolved, the ability to see red led to incorporating reddish hues into monkey looks, by virtue of female preference.

Sexual dimorphism is somewhat common among monkeys, especially the larger species. Male baboons are typically twice the size and weight of females. In contrast, in the smallest New World monkeys – tamarins and marmosets – the sexes are similarly sized.

Monkeys in the wild have a life span of 18–50 years, depending upon species. Larger monkeys are typically longer lived. Life in captivity shortens life expectancy considerably.

Monkeys have long been a popular meat. Human hunters now kill millions each year, pushing many monkeys toward extinction. Relentless deforestation more slowly kills those that are not hunted, by robbing monkeys of their food supplies as well as a decent place to live. Like many other forest creatures, monkeys will be extinct within a few decades.


Many monkeys are arboreal, though some are ground-dwellers, such as patas monkeys and baboons.

Most monkeys are diurnal. The night monkey is a notable exception. It avoids foraging competition by working the night shift.

The length of monkey limbs varies by lifestyle. Monkeys that scramble nimbly amid branches have relatively short arms and legs, aided by prehensile tails. Monkeys that walk and run have longer limbs. Exceptional jumpers, such as the pygmy marmoset, have longer legs, while tree swingers, such as spider monkeys, have longer arms than their legs.

Monkeys range from the tiny New World pygmy marmoset (13–16 cm, 0.12–0.14 kg) to the colorful and highly sexually dimorphic Old World mandrill (male: 75–95 cm, 19–37 kg (though some grow to 54 kg); female: 55–66 cm, 10–15 kg).


Monkeys are categorized by continent: either Old World (Africa, Asia) or New World (South and Central America). Old World monkeys (Cercopithecids) are more closely related to hominids than New World monkeys (Platyrrhines).

In geological time, the Atlantic Ocean has been a widening gap between Africa and South America, which separated over 65 MYA. Perhaps as late as 40 MYA, simian conquistadors came from the dark continent to the New World.

Old World monkeys spread from Africa into Asia and Europe during the Miocene epoch (23–5.3 MYA).

Old World monkeys differ from New World in several ways. On average, New World monkeys tend to be smaller than Old World. Almost all New World monkeys are arboreal. Old World monkeys have a wider range of habitat and are more terrestrial.

Taxonomy of monkeys has been an ongoing dispute. This is incidental to appreciating the diversity of lifestyles that these intelligent creatures have.


New World monkeys have a different dentition than Old World: an evolutionary matter of diet. Whereas Old World monkeys have 32 teeth, New World monkeys have 36.

New World monkeys are generally frugivores, supplemented by small insects and other invertebrates, though some also eat leaves. Old World monkeys are primarily folivores (leaf eaters), though Old World monkey diet varies; most are nominally omnivores.

Generally, most monkeys are opportunists that will eat anything that is digestible. African mangabeys rely heavily upon fruit and flowers, but they are not above ripping the bark off trees to snatch anything edible that crawls beneath. Mangabeys also hunt for birds’ nests, devouring both eggs and nestlings when found.

Monkeys love fruit, though they can quite wasteful: taking a bite or two before chucking it, as it is often not ripe enough to suit their taste. There is some socially inspired conflict in this.

Monkeys are actually quite adept at discerning just how ripe a fruit is. They prefer to wait for the sweetness that comes with ripening.

But if they wait too long, they may lose the fruit to another. So, they often compromise by picking early and eating only the best part rather than risk losing the whole thing.


Most monkeys live in tropical rainforests. The farther one travels from the equator, the fewer monkeys. This makes sense in light of their diet, which is heavily dependent upon fruit and leaves.

There are exceptions. Baboons are successful savanna residents, as is the ground-dwelling patas monkey, which feeds on insects, gum, seeds, and tubers. The hamadryas baboon lives in the dry, rocky regions of southern Arabia.

Most monkeys live warm climates, though there are exceptions. A few tropical monkeys live well about the snow line of mountains, including the African vervet, the Asian snub-nosed langur, and several species of macaques. The Japanese macaque survives the cold winters of northern Honshū; the only nonhuman primate to live so far north.


With a few exceptions, New World monkey vision is dichromatic (2-color), whereas Old World monkeys are trichromatic (3-color), as are humans.

New World monkey noses are flat, with nostrils to the side. Old World monkeys have human-like down-facing noses.

Unlike Old World monkeys and humans, New World monkeys don’t have opposable thumbs, with one exception. The capuchin, a New World monkey, does have an opposable thumb.

Polygyny (males mating multiple females) predominates with Old World monkeys. In contrast, several New World monkeys are monogamous, with extensive parental care.

Unlike apes, almost all monkeys have tails, as do prosimians. Some tails are quite short, such as the mandrill.

Only the Barbary macaque entirely lacks a tail. This macaque is endemic to the Atlas Mountains of Algeria and Morocco, with a small population on Gibraltar.

New World monkeys have relatively longer tails than Old World monkeys.

The atelid family of New World monkeys are the only primates with a prehensile tail, which is useful as a 5th limb for foraging or climbing. Howler, spider, and woolly monkeys are atelids.

Prehensile tails are not a common animal trait. New World mammals with prehensile tails include the opossum, kinkajou (honey bear), and porcupine. The harvest mouse, tree pangolin (scaly anteater), and bearcat (binturong) are the few Old World mammals with prehensile tails.


Monkeys are typically noisy, with a rich repertoire of communications, including combinations and expressions of considerable nuance. Monkeys are quite sensitive to changes of expression on each other’s faces.

New World monkeys are especially exuberant. It helps keep the group together. Tiny marmosets constantly call to each other, twittering like birds as they scamper through the branches.

Female squirrel monkeys are the top talkers: ceaselessly communicating as they move through the forest. Losing sight of one another results in a call-and-response series of high-pitched peeps. Other squirrel monkey sounds have their own syntax. Females that direct a troop twitter to get others moving. A “chuck” sound is a call reserved for close friends.


Monkeys have an innate sense of fairness and are naturally empathic. Rhesus macaques will not perform an action if they think it will harm a conspecific.

Whatever social finery humans possess they inherited from monkeys. The difference in human social proclivities is some liberation from biologically-bound mores to allow selfishness fuller flower.

Monkeys are gregarious. Groupings vary by species, but all monkeys have social organizations.

All societies are rule-based to some degree, though monkey mores tend to be relatively relaxed in those that live in the trees. For example, African mangabey groups are nominally led by a male who does not exercise much control over group activities. Members come and go frequently.

Ground-dwellers tend to live in controlled societies. Baboons have a patriarchal social system that is tightly managed: members seldom leave their group, and newcomers are not normally welcome.

Security is one evolutionary impetus for social organization. The trees are nominally safer than the ground; hence the difference in liberality between species with different lifestyles.

Baboon and patas monkeys stay safe via discipline among male members who have assigned roles for security detail and other duties. Every member knows its station and its duty to the group.

Such social organization has enveloping effects. Competition for food is frequent. Rules determine who gets the best food. Breeding is controlled in stricter societies.

Monkeys simultaneously compete and depend upon each other. They remember kindnesses and conflicts. A monkey knows who it can depend on and who will stand in its way.

Might makes right in monkey society. Dominant members dole out discipline as deemed necessary: whether physical punishment or reduction in food rations for some duration.

Subordinates are careful to stay on the good side of those above them. A monkey seeks to groom another that it is afraid it would lose a fight with.

Spectators gather round when 2 monkeys fight. Immediately afterwards, a bystander approaches the loser, seemingly to console. Mutual grooming often ensues between the two. More often than not, the loser grooms the bystander for longer than the bystander grooms the loser. The bystander takes advantage of the loser’s diminished sense of self.


Grooming as placation is a mainstay in maintaining close relations. Monkey grooming is analogous to human manners, often with similar social considerations.

Grooming is extensively practiced by females that stay in the same troop their whole lives. They know one another well. Each female is aware of hers and others ranks. Grooming cements bonds.

Males need allies too. A dominant male baboon is less vulnerable to attack by an ambitious upstart with another large male by his side. Learning whom to groom is a necessary skill.

The need for close bonds depends on many factors but food looms large. When there is enough food for all, competition is low. Bonding is less critical in times of plenty. Grooming is occasional.

Scarcity brings struggle. Grooming increases during tense times, to keep friends close, and to curry favor.


Monkeys have a fascinating mix of mental acumen. Monkeys remember where different fruit trees are and when they ripen. This requires spatial mental maps correlated to calendars.

Monkeys manage math, especially quantities. Rhesus monkeys understand the relations of numbers and can perform mental addition.

Sociality is paramount to leading a successful monkey life. A monkey needs to know who belongs and who does not, who is related to whom, the relative ranks of every monkey in the group, and the special grooming relationships group members have with each other. Monkeys have distinct personalities which must be accounted for. A monkey must keep in mind which relationships are valuable to cultivate, and how, and who should be assiduously avoided.

A male bonnet macaque, when challenged by another troop member, will often seek out another male for assistance. The beset macaque will seek an ally that he knows outranks the monkey challenging him. The presence of a higher-ranking male renders the challenger much less eager for a confrontation.

Monkey pettiness has a distinctly human edge. They squabble among themselves. To answer an attack, a monkey may not directly confront the attacker, but instead take revenge on a relative or friend of the other monkey, even though the victim played no part.


Deliberate deception is a monkey trait; something which requires thoughtful anticipation of another’s expectations (theory of mind). Baboons are especially adept at deception.

A juvenile baboon watched an adult female dig a plant bulb from the ground. The youngling scanned the scene; no one else nearby. So, it screamed its lungs out for help. Mom came running. Spotting the other female, she instantly assumed that her precious child had been attacked. The outraged mother went after the puzzled innocent female, who dropped the bulb and ran. The now calm and contented youngster casually picked up the tasty bulb. This was not the only incident observed of this child pulling this trick.