Primates are everywhere in Western entertainment: King Kong, Curious George, Grape Ape, Donkey Kong, King Julien, Mort, and “Monkey” from Kung Fu panda. Primates also appear in Japanese folklore in tales like the Monkey and Crab. Baboons figure prominently in Egyptian mythology, sometimes being associated with virility and sometimes with Thoth the god of writing. Among the class Maya, howler monkeys are associated with artisans and scribes. The Greek Cercopes were mischievous brothers whom Zeus turned into monkeys. Typically, the monkeys in these tales are up to no good, and receive comeuppance for deviousness and lying. But what are primates exactly, and how can they shed light on what it means to be human?
As we have seen, humans have much in common with other animals, especially apes and monkeys. We have in common tools, reasoning, complex sociality, reciprocity and even culture, according to some definitions. We also share susceptibility to many of the same zoonotic diseases like polio, measles, and ebola. Because humans share so much in common socially and biologically with apes, monkeys and similar species, we are all classified in the same family called the Primates. Primatology is a sub-discipline of biological anthropology that focuses on primate behavior, biology, and conservation.
All animals are classified according to the their similarities and differences. Carolus Linnaeus (1707-1778) was a Swedish botanist who set out to categorize all of Earth’s animal and plant species according to their physical similarities and differences, or their morphology, in his Systema Naturae. Most of us are familiar with the genus and species system of the taxonomy called the binomial system, meaning two-name system. Our own genus is “Homo” and our species is “sapiens”, meaning “wise man”. Prior to Linnaeus many people subscribed to the idea of the Great Chain of Being a classification system of rocks, species, and divine beings ranked according to their moral perfection. God is at the top of the chain and dirt at the bottom. The system that Linnaeus initiated is not based on ranking species according to better or worse, but rather on their physical similarities, and more recently genetic similarities.
The taxonomy that Linnaeus created in the 18th century is still in use today. The categories of the classification become increasingly more narrow, like nested dolls. The broadest category in kingdom, as in the animal and plant kingdoms. The other categories are phylum, class, order, family, genus, and species. (The category of domain was added before kingdom in recent years). Primates is an Order in the taxonomic system. There are about 300 species of primates most of which live in tropical climates making it one of the largest groups of mammals in the world. The Catalogue of Life is an online database of the world’s known species, containing 1.64 million species of the estimated 1.9 million species in the world.
What is a Primate?
You are likely familiar with the Class called Mammalia. Mammals share a number of features. Mammal characteristics include:
- Nurse Young
- Live Young
Primates are a group within the Class Mammalia, and so they share all the features of mammals. But they also share a number of features in common that are absent in other mammals. Some of these common tendencies are morphological and others revolve around life history, features having to do with the timing and duration of life events. Not all primates have every single trait listed and so these can be thought of as primates trends or tendencies.
- Relatively long period of immaturity compared to other mammals marked by learning the social and physical environment
- Late sexual maturity
- Few offspring
- High degree of parental investment in offspring
- Complex sociality (grooming, alliances, conflict)
- Grasping hands (some have opposable thumbs)
- Stereoscopic vision (visual fields overlap for 3D vision)
- Relatively large brain to body size
- Reduced sense of smell
Physical Features of Primates
The primate hand has five fingers and is capable of grasping (but the spider monkey is an exception with no thumb). Some primates like apes and Old World monkeys have true opposable thumbs, meaning the thumb can be oriented in opposition to the other digits. Grasping hands allows primates to manipulate their environment and for some, make and use tools. Primates have an expanded capacity for touch, especially by the hands, rather than smell. Some primates, especially those that are arboreal, living in trees, also have grasping feet.
Primates tend to have relatively poor smell, but keen eyesight. Mammals in general have about the same number number of genes that influence sense of smell. In primates, many of these genes are no longer functioning. The genes are either turned off by regulator genes or are deactivated by mutations. Primates instead are the “most visually adapted order of animals” (Heesy 2009). All primates have fields of vision that overlap, which allows for keener three-dimensional depth perception called stereoscopic vision or stereopsis. With stereoscopic vision, the fields of view overlap and the two different images seen by each eye are combined in the brain to form a three-dimensional image. Because many primates are arboreal, it has been suggested that keen eyesight is critical for judging distance and depth of tree branches. Others argue that this type of vision developed in relation to predation of insects. A binocular field of vision is common in predators who need to judge distances. Non-overlapping fields of view are more common in prey animals, who need a wider field of vision to spot predators.
Primates tend to live in social groups. Social grooming is especially important for many primates. Baboons who groom each other regularly, are more likely to come to each other’s aid in a crisis. Thus social grooming is a form of reciprocity (exchanging favors). There are exceptions, for example, orangutans lead mostly solitary lives.
Primates also have larger than expected brains for their body size. This is called the encephalization quotient. In addition, brain areas associated with memory, thought, and association are increased in primates. Primates proportionally devote more brain to the neocortex than any other animal. The neocortex is the seat of cognition, memory, abstractions, philosophy and so forth. As we have seen, primates can solve complex problems and chimpanzees outcompete humans on some memory tasks.
Primates use flexible thinking not only to forage for patchily distributed food and solving physical problems, but also to negotiate group dynamics. Primates often live in socially complex groups, and must form and manage social ties (called affiliation) and avoid conflict (called agonism). Chimpanzees males often work together and cooperate to dominate other chimpanzees. Another socially complex aspect of primate life is dispersal. Dispersal occurs when males or females move out of their natal group at maturity and join another group. As with human exogamy, moving out of one’s natal group can be a risky endeavor, requiring skillful negotiation. Not so different from humans, the social lives of primates can be stressful. Robert Sapolsky has studied the stressful effects of baboon social life. He spent 30 years darting African baboons to check their hormone levels, a measure of how much stress they experience. Sapolsky learned that baboons, especially low-ranking baboons and baboons who lack social connections have high stress levels and poor health. As Sapolsky puts it “Primates are super smart and organized just enough to devote their free time to being miserable to each other and stressing each other out” (Shwartz 2007).
In addition, primate infants take a long time to develop and a strong mother-infant bond develops. Most primates give birth to a single offspring and offspring often receive extensive care called “parental investment” from the mother or, less commonly, from both parents. During this long period of dependency, the infant learns appropriate behavior and how to solve problems. Humans stand out in this arena with an impressively long period of juvenile dependence.
There are a number of groupings within the Primate order. These groups indicate how closely related the primates are. When there is genetic and morphological similarity between species, we assume they also share a common ancestry or phylogeny. The ancestry of of primates can be charted. Note that the this diagram is not linear, but branching. The Prosimians (Strepsirrhini) and Tarsiers, Monkeys, Apes and Humans (Haplorrhini) are suborders within the Primate order. Suborders are broken down further into families and superfamilies.
Suborder: Strepsirrhini: Prosimians
Suborder: Haplorrhini: Tarsiers, Monkeys, Apes, Humans
Family: Tarsiiformes: Tarsiers
Family: Simiiformes: Monkeys, Apes, Humans
Superfamily: Cercopithecoidea: Old World Monkeys from Asia and Africa
Superfamily: Ceboidea: New World Monkeys
Superfamily: Hominoidea: Apes and Humans
Prosimians are thought to have branched off from the primate line earliest and are therefore different in many respects from other primates. That is, they retain features of earlier fossil primates. They tend to be smaller, more often nocturnal, better smellers, less social and more insectivorous (insect eaters) than other primates. Three broad groups of prosimians are lorises, galagos, pottos, and lemurs. Lemurs only live on the island of Madagascar (where there are no monkeys) and have diversified into more than 30 species, all of which are endangered. Most lemurs are arboreal, or tree-dwelling, but others are terrestrial, living on the ground. Arboreal lemurs move about mainly by clinging and leaping. Because their bodies are adapted for leaping, lemur legs are long in comparison to their arms. While ideal for moving among branches, moving on the ground results in an odd balletic leaping movement.
Lemurs have elongated legs for leaping.
Some lemurs are nocturnal while others are diurnal, active during the day. Body size and diet of lemurs varies considerably. Some lemurs have interesting and unexpected behaviors. For example, black lemurs bite into poisonous millipedes, which can act as an insect repellent (Birkinshaw 1999). Primatologist Louise Peckre and colleagues (2018) found that lemurs rub the millipedes on their anuses to prevent threadworms from laying eggs on their anal regions.
Lorises are omnivorous, solitary, and arboreal, meaning they live in trees. The Javan slow loris is now critically endangered due to the illegal pet trade, use in traditional medicines, and deforestation. The slow loris (Nycticebus javanicus) is the only venomous primate. Although owning slow lorises as pets is illegal, they have appeared as pets in popular Youtube videos. According to primatologist Anna Nekaris (2013), when kept as pets, loris teeth are painfully removed, and they are exposed to bright lights which can blind them because they are nocturnal. Nekaris argues that social media on the whole is harming rather than helping the slow loris and advocates for Youtube to have a way for people to police animal cruelty videos. “Bushbabies” also called galagos are another well-known species of loris.
Tarsiers were once thought to be in the prosimian group, but through genetic research are now known to be closer to monkeys and apes. All tarsiers live in Southeast Asia and are arboreal, nocturnal, insectivorous and very small.
New World Monkeys
New World monkeys (family Ceboidea) live only in Central and tropical South America. These monkeys have been separate from Old World monkeys since the separation of South America from Africa. The New World monkeys are mainly arboreal and most are diurnal, active during the day and sleeping at night. Some New World monkeys, like howler and spider monkeys, also have prehensile tails, meaning they can be used to grasp tree branches. Old World monkeys of Africa and Asia do not have prehensile tails. These monkeys have flat noses with wide-spaced nostrils and are called the platyrrhines, meaning “flat-nosed”. The are 64 species of New World monkeys consisting of two groups: tamarin/marmoset and Cebid monkeys.
The 20 species of tamarins and marmosets tend to small and feed off the gum of trees and are called gumivores. The pygmy marmoset of the Amazon Basin is the smallest primate and is around five inches long. Cebid monkeys are larger, some with prehensile tails, and eat fruits, insects, and leaves. Some well-known cebid monkeys include spider monkeys, howler monkeys, squirrel monkeys, and capuchin monkeys.
New world tamarin monkey: cotton-top tamarin (Saguinus oedipus; critically endangered)
New World tamarin monkey: Golden Lion Tamarin (endangered).
New World marmoset: Geoffroy’s marmoset.
New World cebid monkey: Capuchin monkeys of Costa Rica.
New World cebid monkey: The Howler monkey, Belize.
New world cebid monkey: Uakari, Amazon region, South America.
New World cebid monkey: The squirrel monkey.
Old World Monkeys
The approximately 75 species of Old World monkeys live in Africa and South Asia and are typically larger than their New World counterparts. They have more closely spaced nostrils and their noses are less flat than New World monkeys. Because of this distinction, the are often referred to as the catarrhines. Old World monkeys can be placed into two groups: the colobines and cercopithecines. The colobines mostly live in southern Asia and the cercopithecines live mostly in Africa. All New World monkey species live in social groups.
Langurs are a well-known colobine species. Several species of langurs are endangered or critically endangered like the grey-shanked douc (Pygathrix cinerea) of Vietnam. This Old World monkey is losing ground to agriculture, logging, hunting, and the pet trade. At least four other langur species are also critically endangered. Another well-known colobine monkey (Nasalis larvatus) is the proboscis monkey of Southeast Asia. The males and females of this species are sexually dimorphic. Sexual dimorphism refers to differences in “secondary sexual characteristics” like size, weight, coloration, and behavior. Males have much larger noses than females (sexual dimorphism), which can be up to 10 cm. These unusual monkeys are now endangered.
Old World colobine monkey (Vietnam): The Grey-shanked Douc Langur (Pygathrix cinerea) is one of the most endangered primates in the world.
Colobine monkeys of southern Asia: Proboscis monkeys (Nasalis larvatus)
The cercopithecine monkeys live mostly in tropical Africa. They tend to have larger bodies than colobines. Some cercopithecine monkeys have moved into savanna environments and are largely terrestrial, living mostly on the ground. Terrestrial monkeys like baboons have ischial callosities informally known as “butt patches”, which are an adaptation to sitting on the ground. Terrestrial monkeys also tend to be sexually dimorphic. Male baboons, for example, are larger than females and have longer canines. Macaques, baboons, mangabeys, and guenons are examples of cercopithecines.
Old world cercopithecine monkey (Japan): Japanese macaque (Macaca fuscata)
Old World cercopithecine monkeys (Africa): Chacma baboon (Papio ursinus).
Old World cercopithecine monkeys (Africa): Gelada baboon (Theropithecus gelada).
Old World cercopithecine monkey (Africa): lesser spot-nosed guenon (Cercopithecus petaurista).</p
All apes live in the Old World, either in Africa and southern Asia. Compared to monkeys, apes are large-bodied, large-brained, and most are terrestrially adapted. Also, unlike monkeys, apes do not have tails. The ape shoulder has greater rotation than monkeys allowing them to hang and swing from branches. All apes are diurnal, active during the day. Apes are more closely related to Old World monkeys than New World monkeys. Apes are divided into the lesser apes or gibbons and the great apes. The great apes, gorillas, chimpanzees, bonobos, and orangutans, are the largest of all primates. Gorillas, chimpanzees and bonobos live in tropical Africa, while the orangutan lives in southeast Asia on only two islands of Indonesia. Most are primarily herbivorous eating leaves or fruits, and to a lesser extent in some species insects and meat. The African great apes live in complex social groups, while the orangutan is mainly solitary. All great apes are endangered.
The lesser apes live in southeast Asia and are smaller than other apes with smaller brains. Lesser apes are mainly arboreal and have a particular type of locomotion called brachiation. Brachiation involves swinging from branch to branch by the arms, including a phase of free-flight. Lesser apes resemble monkeys, but they lack tails. Lesser apes often live in socially monogamous pairs, but males do not typically provide much in the way of parental investment. The lesser apes are various types of gibbons.
Gibbons are lesser apes and live in southeast Asia.
Gorillas are the largest of the apes and live exclusively in Africa. The gorilla lives in social groups called troops consisting of 10-20 gorillas including the the silverback male, adults females and their children. The silverback male, named for the silvery hair that develops on his back and rump, is the only breeding male in the group and he protects his reproductive access to females in the group. As in humans, this this is referred to as polygyny. Males (350 lbs.) tend to be much larger than females (155 lbs.), exhibiting a high degree of sexual dimorphism or difference in form between males and females.
Gorillas have a mainly vegan diet of leaves sometimes supplemented with ants, and spend most of their waking hours eating. Gorillas locomote by knuckle-walking, that is, they walk on the knuckles of their hands rather than on their palms. Gorillas are mostly terrestrial, typically building nests on the ground for sleeping. Infants are helpless and require a high degree of parental investment from the mothers. Newborn gorillas nurse at least once per hour. Silverbacks will protect offspring from aggression and socialize juveniles. The lifespan of a gorilla in the wild is between 35 and 40 years.
There are two general varieties of gorilla, the western gorilla and the eastern gorilla, all of which are critically endangered. “Critically endangered” is the last survival status above extinct. Mountain gorillas are a well-known eastern gorilla (Gorilla beringei beringei) living in central Africa in the Congo, Rwanda, and Uganda in the vicinity of the Virunga volcanoes. Numbering only about 880 individuals, they are critically endangered. Threats to mountain gorillas include poaching, political unrest, and loss of habitat die to human expansion. Fortunately, mountain gorilla numbers are increasing since an all-time low in the 1980s of 254. The lowland eastern gorilla population, however, declined 70% in the last 20 years. There are no mountain gorillas in captivity. Previous attempts at captivity have resulted in death.
Orangutans lives exclusively in Indonesia on Sumatra and Borneo and are the only great ape to live outside Africa. Orangutans differ from other great apes in that they are mainly solitary, and live high in the rainforest canopy. Orangutans live mainly on fruits and leaves, and like all great apes build nests. They’ve even been known to fashion leaf umbrellas to protect themselves form rain. Orangutans make a unique kissing sound called a “kiss squeak” when they are agitated. Like gorillas, orangutans have sexual dimorphism, with males being twice the size of females. Orangutans are critically endangered due to the pet trade, logging, and palm oil production. Palm oil is especially endangering orangutans, destroying the last orangutan habitat to make way for palm oil plantations. Like other apes, orangutan infants require a great deal of maternal care, staying with their mothers for six years. Orangutans are particularly suceptible to extinction because of they reproduce only every 7 or 8 years, the longest birth spacing among mammals. In the 1970s, Biruté Galdickas famously studied Bornean orangutans in the wild and tried to reintroduce captive pet infant and juvenile orangutans back into the wild. This required a great deal of care of the part of Galdikas, even to the point of sleeping with infant orangutans and waking up in a puddle of orangutan urine and feces(Galdikas 1996). Because of the intense parent-infant bond, Galdikas also had to carry an orangutan infant through the sometimes flooded forest in order to make her observations on orangutans.
Chimpanzees and Bonobos
There are two species of chimpanzees, Pan troglodytes (chimpanzees) and Pan paniscus (bonobo). Chimpanzees live in tropical Africa as well as a savanna environment. Like gorillas, chimpanzees are knuckle-walkers. Chimpanzees spend time on the ground and in trees. They prefer fruits and also occasionally eat protein such as mammals, birds, or eggs. Chimpanzees are less sexually dimorphic than gorillas, though males are somewhat larger. Chimpanzees form multi-male and multi-female troops of up to 60 chimps, but typically travel in smaller parties. Of all the primates, they have the highest incidence of tool use, using termite and ant sticks, rocks for nut cracking, leaf sponges, and even a kind of trusting spear. Female chimpanzees use tools most often.
Males tend to be dominant among chimpanzees. Females move out of their group upon sexual maturity while males remain. This allows males to form coalitions. The coalitions are critically important and based on friendships cemented through grooming—literally scratching each other’s’ backs. For this reason, chimpanzees are often described as “political”. Dominant males will have preferential access to food and sexual partners. Males also perform dramatic displays—hooting, jumping, dragging objects, and thumping— designed to intimidate other males. Males will also hunt on occasion and eat more meat the females. Chimpanzees and bonobos are the only adult primates besides humans to share food. Chimps share food for many of the same reasons humans do—to support close relatives (mother to offspring), to support friendships (reciprocal altruism), and tolerated theft (protecting the food more costly than sharing).
Among chimpanzees, females, rather than males, move out of their natal troop into a new troop (dispersal). Males remain in their natal troop and form reciprocal bonds and strong male-male relationships. They also defend their territory and perform silent boundary patrols of their territory. Jane Goodall reported one troop of chimpanzees systematically killing all the males in a neighboring troop that had splintered off from the first group.
Chimps use a wide range of vocalizations from grunts to pant-hoots. They also use gestures. The outstretched hand, is used to request an item usually food. Unlike humans, chimps do not point in the wild, but can be taught to do so in captive environments.
Female chimpanzees undergo an obvious ovulation cycle called estrus, which is marked by a large red genital swelling. Male chimp are only interested in copulation during estrus. Male chimpanzees also prefer to mate with older females because they are more competent mothers than younger female chimpanzees.
Bonobos have been isolated from chimpanzees for about a million years. While bonobos look very similar to chimpanzees, the are socially very different. Among bonobos, females tend to be more dominant and females display by dragging objects. Males bonobos, who stay in their natal group, get their status from their high-ranking mothers. Overall, bonobos are less aggressive than chimpanzees and resolve social tension through sexual behavior. Bonobos engage in non-reproductive sexual behavior, sex not intended for reproduction, by rubbing genitals and other sexual behavior. This non-reproductive behavior is used to alleviate social stress, especially among females. Bonobos are not the only non-human primates to engage is same-sex interactions. Japanese macaques in Mindoo in central Japan exhibit female-female sexual interactions and even monkey-deer sexual interactions (Gunst et al. 2018).
Since humans and chimps are so similar genetically, chimp biomedical research began in the United States in the 1960s. Chimps were taken from Africa and sent to newly created primate research centers. The U.S. government stopped importing chimpanzees from Africa in 1973 and began a breeding program. Captive chimps reached their peak in 1996 when 1500 chimpanzees lived at primate centers, including one in Alamogordo, New Mexico. In 2013, a report came out from the Institute of Medicine saying that invasive research on chimpanzees was unnecessary and as a result the National Institutes of Health decided to stop supporting invasive research on chimps (Kaiser 2013). The U.S. Fish and Wildlife Service (USFWS) declared U.S. captive chimps endangered ending all biomedical research (Grimm 2015). All but 50 of the 350 federally owned chimps were slated for retirement (Grimm 2017). Chimp Haven near Shreveport, Louisiana, is a retirement sanctuary for biomedical research chimps. But retirement has been slower than expected due to funding, health issues, transportation, and difficulties with reintegration. Today, the Alamogordo Primate Research Facility still houses 126 chimps.
Primate Conservation: The Human Toll
The relationship between humans and other primates has been the source of increasing study and interest and now has its own name, ethnoprimatology. According to a 2017 study, 60 percent of primates are threatened with extinction and 75 percent of species are declining (Estrada et al. 2017). Perhaps not too surprisingly, people are the problem. Logging, deforestation, mining, poaching, and social unrest are common causes of primate decimation. Protecting primates is not a simple task. As many as 150 rangers in Virunga National Park, Africa’s oldest national park and mountain gorilla refuge, have lost their lives defending the park and the gorillas from poachers and rebel militias (Howard 2016). Today, thanks to the continued dedication of the rangers, the numbers of mountain gorillas in the park are low but increasing. Sadly, Virunga National Park closed in 2018 in response to the murder of a ranger and the kidnapping of two tourists and their driver (Sims 2018).
Mountain gorilla conservation has not been straightforward with regard to local populations. The Batwa forest dwellers of Uganda were displaced from the Bwindi Impenetrable forest where they lived as hunter-gatherers for almost certainly thousands of years. The Batwa were removed at gunpoint to make way for a mountain gorilla national parks (Bwindi Impenetrable and Mgahinga Gorilla National Parks) and gorilla ecotourism. The Batwa were not compensated for their land because as traditional hunter-gatherers there was no land ownership. Today, the Batwa live on the periphery of their ancestral lands, unable to hunt and gather in the forest. Child mortality is high, with 40 percent dying before the age of five. Batwa work as farm hands for food or low wages or sometimes they dress in fake animal skins and dance for tourists. In a recent article for the BBC, it was reported, “According to Mr Muhangi from the wildlife authority, from each $600 fee paid by a tourist for a gorilla trek, $8 is allocated to local communities but nothing goes directly to the Batwa” (BBC News 2016). They also face extreme discrimination. One woman was set on fire for foraging in a farmer’s garden (she survived). Recently, a Batwa man was arrested for killing a duiker, a small antelope, and is being held by police (Survival International 2017). As a result of their eviction, the Batwa live in squalor, and malaria, AIDS, malnutrition and alcoholism have taken hold. The Batwa, in effect, have become conservation refugees, not so different from the San who were evicted from the Kalahari Game Preserve.
The Batwa were forcibly removed from the forest to make way for gorilla ecotourism.