Monkey is a common name that may refer to most mammals of the infraorderSimiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, constitute an incomplete paraphyletic grouping; however, in the broader sense based on cladistics, apes (Hominoidea) are also included, making the terms monkeys and simians synonyms in regard to their scope.
In 1812, Étienne Geoffroy grouped the apes and the Cercopithecidae group of monkeys together and established the name Catarrhini, “Old World monkeys” (“singes de l’Ancien Monde” in French).[3][4][5] The extant sister of the Catarrhini in the monkey (“singes”) group is the Platyrrhini (New World monkeys).[3] Some nine million years before the divergence between the Cercopithecidae and the apes,[6] the Platyrrhini emerged within “monkeys” by migration to South America from Afro-Arabia (the Old World),[citation needed][7][8] likely by ocean.[9][10][better source needed] Apes are thus deep in the tree of extant and extinct monkeys, and any of the apes is distinctly closer related to the Cercopithecidae than the Platyrrhini are.
Many monkey species are tree-dwelling (arboreal), although there are species that live primarily on the ground, such as baboons. Most species are mainly active during the day (diurnal). Monkeys are generally considered to be intelligent, especially the Old World monkeys.
Within suborder Haplorhini, the simians are a sister group to the tarsiers – the two members diverged some 70 million years ago.[11] New World monkeys and catarrhine monkeys emerged within the simians roughly 35 million years ago. Old World monkeys and apes emerged within the catarrhine monkeys about 25 million years ago. Extinct basal simians such as Aegyptopithecus or Parapithecus (35–32 million years ago) are also considered monkeys by primatologists.[9][12][13][14][15][16]
Apes emerged within monkeys as sister of the Cercopithecidae in the Catarrhini, so cladistically they are monkeys as well. However, there has been resistance to directly designate apes (and thus humans) as monkeys, so “Old World monkey” may be taken to mean either the Cercopithecoidea (not including apes) or the Catarrhini (including apes).[17][18][19][20][21][22][23][24][25] That apes are monkeys was already realized by Georges-Louis Leclerc, Comte de Buffon in the 18th century.[26]Linnaeus placed this group in 1758 together with the tarsiers, in a single genus “Simia” (sans Homo), an ensemble now recognised as the Haplorhini.[27]
Macaque on a “Please do not feed monkeys” sign in Ko Chang, Thailand.
Monkeys, including apes, can be distinguished from other primates by having only two pectoral nipples, a pendulous penis, and a lack of sensory whiskers.[28][better source needed]
According to the Online Etymology Dictionary, the word “monkey” may originate in a German version of the Reynard the Fox fable, published c. 1580. In this version of the fable, a character named Moneke is the son of Martin the Ape.[29] In English, no clear distinction was originally made between “ape” and “monkey”; thus the 1911 Encyclopædia Britannica entry for “ape” notes that it is either a synonym for “monkey” or is used to mean a tailless humanlike primate.[30] Colloquially, the terms “monkey” and “ape” are widely used interchangeably.[31][32] Also, a few monkey species have the word “ape” in their common name, such as the Barbary ape.
Later in the first half of the 20th century, the idea developed that there were trends in primate evolution and that the living members of the order could be arranged in a series, leading through “monkeys” and “apes” to humans.[33] Monkeys thus constituted a “grade” on the path to humans and were distinguished from “apes”.
Scientific classifications are now more often based on monophyletic groups, that is groups consisting of all the descendants of a common ancestor. The New World monkeys and the Old World monkeys are each monophyletic groups, but their combination was not, since it excluded hominoids (apes and humans). Thus, the term “monkey” no longer referred to a recognized scientific taxon. The smallest accepted taxon which contains all the monkeys is the infraorder Simiiformes, or simians. However this also contains the hominoids, so that monkeys are, in terms of currently recognized taxa, non-hominoid simians. Colloquially and pop-culturally, the term is ambiguous and sometimes monkey includes non-human hominoids.[34] In addition, frequent arguments are made for a monophyletic usage of the word “monkey” from the perspective that usage should reflect cladistics.[21][35][36][37][38]
Several science-fiction and fantasy stories have depicted non-human (fantastical or alien) antagonistic characters refer to humans as monkeys, usually in a derogatory manner, as a form of metacommentary.[39]
A group of monkeys may be commonly referred to as a tribe or a troop.[40]
Two separate groups of primates are referred to as “monkeys”: New World monkeys (platyrrhines) from South and Central America and Old World monkeys (catarrhines in the superfamily Cercopithecoidea) from Africa and Asia. Apes (hominoids)—consisting of gibbons, orangutans, gorillas, chimpanzees and bonobos, and humans—are also catarrhines but were classically distinguished from monkeys.[41][9][42][43] Tailless monkeys may be called “apes”, incorrectly according to modern usage; thus the tailless Barbary macaque is historically called the “Barbary ape”.[32]
Description
As apes have emerged in the monkey group as sister of the old world monkeys, characteristics that describe monkeys are generally shared by apes as well. Williams et al. outlined evolutionary features, including in stem groupings, contrasted against the other primates such as the tarsiers and the lemuriformes.[44]
Monkeys range in size from the pygmy marmoset, which can be as small as 117 mm (4+5⁄8 in) with a 172 mm (6+3⁄4 in) tail and just over 100 g (3+1⁄2 oz) in weight,[45] to the male mandrill, almost 1 m (3 ft 3 in) long and weighing up to 36 kg (79 lb).[46] Some are arboreal (living in trees) while others live on the savanna; diets differ among the various species but may contain any of the following: fruit, leaves, seeds, nuts, flowers, eggs and small animals (including insects and spiders).[47]
Some characteristics are shared among the groups; most New World monkeys have long tails, with those in the Atelidae family being prehensile, while Old World monkeys have non-prehensile tails or no visible tail at all.[32] Old World monkeys have trichromaticcolor vision like that of humans, while New World monkeys may be trichromatic, dichromatic, or—as in the owl monkeys and greater galagos—monochromatic. Although both the New and Old World monkeys, like the apes, have forward-facing eyes, the faces of Old World and New World monkeys look very different, though again, each group shares some features such as the types of noses, cheeks and rumps.[47]
Classification
The following list shows where the various monkey families (bolded) are placed in the classification of living (extant) primates.
Below is a cladogram with some extinct monkey families.[48][49][50] Generally, extinct non-hominoid simians, including early catarrhines are discussed as monkeys as well as simians or anthropoids,[41][9][42] which cladistically means that Hominoidea are monkeys as well, restoring monkeys as a single grouping. It is indicated approximately how many million years ago (Mya) the clades diverged into newer clades.[51][52][53][54] It is thought the New World monkeys started as a drifted “Old World monkey” group from the Old World (probably Africa) to the New World (South America).[9]
Macaque on a “Please do not feed monkeys” sign in Ko Chang, Thailand.Sign at a store in Swyambhunath, Bagmati, Nepal, which reads “Monkey’s Food is Available here”. Some places use their monkey population as a tourist attraction.
The many species of monkey have varied relationships with humans. Some are kept as pets, others used as model organisms in laboratories or in space missions. They may be killed in monkey drives (when they threaten agriculture) or used as service animals for the disabled.
In some areas, some species of monkey are considered agricultural pests, and can cause extensive damage to commercial and subsistence crops.[55][56] This can have important implications for the conservation of endangered species, which may be subject to persecution. In some instances farmers’ perceptions of the damage may exceed the actual damage.[57] Monkeys that have become habituated to human presence in tourist locations may also be considered pests, attacking tourists.[58]
Some organizations train capuchin monkeys as service animals to assist quadriplegics and other people with severe spinal cord injuries or mobility impairments. After being socialized in a human home as infants, the monkeys undergo extensive training before being placed with disabled people. Around the house, the monkeys assist with daily tasks such as feeding, fetching, manipulating objects, and personal care.[62]
Helper monkeys are usually trained in schools by private organizations, taking seven years to train, and are able to serve 25–30 years (two to three times longer than a guide dog).[63]
The most common monkey species found in animal research are the grivet, the rhesus macaque, and the crab-eating macaque, which are either wild-caught or purpose-bred.[66][67] They are used primarily because of their relative ease of handling, their fast reproductive cycle (compared to apes) and their psychological and physical similarity to humans. Worldwide, it is thought that between 100,000 and 200,000 non-human primates are used in research each year,[67] 64.7% of which are Old World monkeys, and 5.5% New World monkeys.[68] This number makes a very small fraction of all animals used in research.[67] Between 1994 and 2004 the United States has used an average of 54,000 non-human primates, while around 10,000 non-human primates were used in the European Union in 2002.[68]
In space
Sam, a rhesus macaque, was flown to a height of 88,500 m (290,400 ft) by NASA in 1959
A number of countries have used monkeys as part of their space exploration programmes, including the United States and France. The first monkey in space was Albert II, who flew in the US-launched V-2 rocket on June 14, 1949.[69]
Informally, “monkey” may refer to apes, particularly chimpanzees, gibbons, and gorillas. Author Terry Pratchett alludes to this difference in usage in his Discworld novels, in which the Librarian of the Unseen University is an orangutan who gets very violent if referred to as a monkey. Another example is the use of Simians in Chinese poetry.
Hanuman, a prominent deity in Hinduism, is a human-like monkey god who is believed to bestow courage, strength and longevity to the person who thinks about him or Rama.
In Buddhism, the monkey is an early incarnation of Buddha but may also represent trickery and ugliness. The Chinese Buddhist “mind monkey” metaphor refers to the unsettled, restless state of human mind. Monkey is also one of the Three Senseless Creatures, symbolizing greed, with the tiger representing anger and the deer lovesickness.
The Sanzaru, or three wise monkeys, are revered in Japanese folklore; together they embody the proverbial principle to “see no evil, hear no evil, speak no evil”.[74]
The Moche people of ancient Peru worshipped nature.[75] They placed emphasis on animals and often depicted monkeys in their art.[76]
The Tzeltal people of Mexico worshipped monkeys as incarnations of their dead ancestors.
Zodiac
Monkeys as Judges of Art, an ironical 1889 painting by Gabriel von Max.
Gorillas are the largest livingprimates, reaching heights between 1.25 and 1.8 m (4 ft 1 in and 5 ft 11 in), weights between 100 and 270 kg (220 and 600 lb), and arm spans up to 2.6 m (8 ft 6 in), depending on species and sex. They tend to live in troops, with the leader being called a silverback. The eastern gorilla is distinguished from the western by darker fur colour and some other minor morphological differences. Gorillas tend to live 35–40 years in the wild.
There are thought to be around 316,000 western gorillas in the wild, and 5,000 eastern gorillas. Both species are classified as Critically Endangered by the IUCN; all subspecies are classified as Critically Endangered with the exception of the mountain gorilla, which is classified as Endangered. There are many threats to their survival, such as poaching, habitat destruction, and disease, which threaten the survival of the species. However, conservation efforts have been successful in some areas where they live.
The word gorilla comes from the history of Hanno the Navigator (c. 500 BC), a Carthaginian explorer on an expedition to the west African coast to the area that later became Sierra Leone.[1][2] Members of the expedition encountered “savage people, the greater part of whom were women, whose bodies were hairy, and whom our interpreters called Gorillae”.[3][4] It is unknown whether what the explorers encountered were what we now call gorillas, another species of ape or monkeys, or humans.[5] Skins of gorillai women, brought back by Hanno, are reputed to have been kept at Carthage until Rome destroyed the city 350 years later at the end of the Punic Wars, 146 BC.
In 1625 Andrew Battel mentioned the existence of the animal, under the name Pongo:
This Pongo is in all proportion like a man, but… he is more like a Giant in stature, than a man: for he is very tall, [and] hath a man’s face, hollow-eyed, with long haire vpon his browes. His face and eares are without haire, and his hands also. His bodie is full of haire, but not very thicke, and it is a dunnish colour. . . Hee goeth alwaies vpon his legs, and carrieth his hands clasped on the nape of his necke, when he goeth upon the ground… They goe many together, and kill many Negroes that trauaile in the Woods . . . Those Pongos are neuer taken aliue, because they are so strong, that ten men cannot hold one of them…
A century and a half after Battel’s story was published, one writer called Radermacher wrote that “the large species, described by Buffon and other authors as of the size of a man, is held by many to be a Chimera.”[7]
The American physician and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla in 1847 from specimens obtained in Liberia.[8] They called it Troglodytes gorilla, using the then-current name of the chimpanzee genus. The species name was derived from Ancient Greek Γόριλλαι (gorillai) ‘tribe of hairy women’,[9] as described by Hanno.
Evolution and classification
The closest relatives of gorillas are the other two Homininae genera, chimpanzees and humans, all of them having diverged from a common ancestor about 7 million years ago.[10] Human gene sequences differ only 1.6% on average from the sequences of corresponding gorilla genes, but there is further difference in how many copies each gene has.[11]
Until recently, gorillas were considered to be a single species, with three subspecies: the western lowland gorilla, the eastern lowland gorilla and the mountain gorilla.[5][13] There is now agreement that there are two species, each with two subspecies.[14] More recently, a third subspecies has been claimed to exist in one of the species. The separate species and subspecies developed from a single type of gorilla during the Ice Age, when their forest habitats shrank and became isolated from each other.[15][failed verification]Primatologists continue to explore the relationships between various gorilla populations.[5] The species and subspecies listed here are the ones upon which most scientists agree.[16][14]
The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the mountain gorilla, sometimes called the Bwindi gorilla.
Some variations that distinguish the classifications of gorilla include varying density, size, hair colour, length, culture, and facial widths.[15] Population genetics of the lowland gorillas suggest that the western and eastern lowland populations diverged around 261 thousand years ago.[23]
Characteristics
Male gorilla skull
Wild male gorillas weigh 136 to 227 kg (300 to 500 lb), while adult females weigh 68–113 kg (150–250 lb).[24][25] Adult males are 1.4 to 1.8 m (4 ft 7 in to 5 ft 11 in) tall, with an arm span that stretches from 2.3 to 2.6 m (7 ft 7 in to 8 ft 6 in). Female gorillas are shorter at 1.25 to 1.5 m (4 ft 1 in to 4 ft 11 in), with smaller arm spans.[26][27][28][29]Colin Groves (1970) calculated the average weight of 42 wild adult male gorillas at 144 kg, while Smith and Jungers (1997) found the average weight of 19 wild adult male gorillas to be 169 kg.[30][31] Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. The tallest wild gorilla recorded was a 1.95 m (6 ft 5 in) silverback with an arm span of 2.7 m (8 ft 10 in), a chest of 1.98 m (6 ft 6 in), and a weight of 219 kg (483 lb), shot in Alimbongo, northern Kivu in May 1938.[29] The heaviest wild gorilla recorded was a 1.83 m (6 ft 0 in) silverback shot in Ambam, Cameroon, which weighed 267 kg (589 lb).[29] The tallest gorilla in captivity was Gust, who was captured as a baby in Belgian Congo and spent his life at Antwerp Zoo. He was 2.20 m (7 ft 3 in) tall. Males in captivity can be overweight and reach weights up to 310 kg (683 lb).[29]
The eastern gorilla is more darkly coloured than the western gorilla, with the mountain gorilla being the darkest of all. The mountain gorilla also has the thickest hair. The western lowland gorilla can be brown or greyish with a reddish forehead. In addition, gorillas that live in lowland forest are more slender and agile than the more bulky mountain gorillas. The eastern gorilla also has a longer face and broader chest than the western gorilla.[32] Like humans, gorillas have individual fingerprints.[33][34] Their eye colour is dark brown, framed by a black ring around the iris. Gorilla facial structure is described as mandibular prognathism, that is, the mandible protrudes farther out than the maxilla. Adult males also have a prominent sagittal crest.
Gorillas move around by knuckle-walking, although they sometimes walk upright for short distances, typically while carrying food or in defensive situations. A 2018 study investigating the hand posture of 77 mountain gorillas at Bwindi Impenetrable National Park (8% of the population) found that knuckle walking was done only 60% of the time, and they also supported their weight on their fists, the backs of their hands/feet, and on their palms/soles (with the digits flexed). Such a range of hand postures was previously thought to have been used by only orangutans.[35] Studies of gorilla handedness have yielded varying results, with some arguing for no preference for either hand, and others right-hand dominance for the general population.[36]
Studies have shown gorilla blood is not reactive to anti-A and anti-B monoclonal antibodies, which would, in humans, indicate type O blood. Due to novel sequences, though, it is different enough to not conform with the human ABO blood group system, into which the other great apes fit.[37]
A gorilla’s lifespan is normally between 35 and 40 years, although zoo gorillas may live for 50 years or more in rare circumstances. At 68 years, 70 days, Fatou is the oldest gorilla ever; oldest female gorilla ever; oldest living gorilla and oldest living female gorilla. The oldest male gorilla ever was Ozoum, who reached to the final age of 61 years, 24 days.[38] The oldest living male gorilla is Guhonda, aged 54 years, 70 days.
Distribution and habitat
Young gorilla climbing
Gorillas have a patchy distribution. The range of the two species is separated by the Congo River and its tributaries. The western gorilla lives in west central Africa, while the eastern gorilla lives in east central Africa. Between the species, and even within the species, gorillas live in a variety of habitats and elevations. Gorilla habitat ranges from montane forest to swampland. Eastern gorillas inhabit montane and submontane forests between 650 and 4,000 m (2,130 and 13,120 ft) above sea level.[39]
Mountain gorillas live in montane forests at the higher end of the elevation range, while eastern lowland gorillas live in submontane forests at the lower end. In addition, eastern lowland gorillas live in montane bamboo forests, as well as lowland forests ranging from 600–3,308 m (1,969–10,853 ft) in elevation.[40] Western gorillas live in both lowland swamp forests and montane forests, at elevations ranging from sea level to 1,600 m (5,200 ft).[39] Western lowland gorillas live in swamp and lowland forests ranging up to 1,600 m (5,200 ft), and Cross River gorillas live in low-lying and submontane forests ranging from 150–1,600 m (490–5,250 ft).
Ecology
Diet and foraging
Gorillas moving in habitat
A gorilla’s day is divided between rest periods and travel or feeding periods. Diets differ between and within species. Mountain gorillas mostly eat foliage, such as leaves, stems, pith, and shoots, while fruit makes up a very small part of their diets.[41] Mountain gorilla food is widely distributed and neither individuals nor groups have to compete with one another. Their home ranges vary from 3 to 15 km2 (1.2 to 5.8 sq mi), and their movements range around 500 m (0.31 mi) or less on an average day.[41] Despite eating a few species in each habitat, mountain gorillas have flexible diets and can live in a variety of habitats.[41]
Gorilla foraging
Eastern lowland gorillas have more diverse diets, which vary seasonally. Leaves and pith are commonly eaten, but fruits can make up as much as 25% of their diets. Since fruit is less available, lowland gorillas must travel farther each day, and their home ranges vary from 2.7 to 6.5 km2 (1.0 to 2.5 sq mi), with day ranges 154–2,280 m (0.096–1.417 mi). Eastern lowland gorillas will also eat insects, preferably ants.[42] Western lowland gorillas depend on fruits more than the others and they are more dispersed across their range.[43] They travel even farther than the other gorilla subspecies, at 1,105 m (0.687 mi) per day on average, and have larger home ranges of 7–14 km2 (2.7–5.4 sq mi).[43] Western lowland gorillas have less access to terrestrial herbs, although they can access aquatic herbs in some areas. Termites and ants are also eaten.
Gorillas rarely drink water “because they consume succulent vegetation that is comprised of almost half water as well as morning dew”,[44] although both mountain and lowland gorillas have been observed drinking.
Gorillas construct nests for daytime and night use. Nests tend to be simple aggregations of branches and leaves about 2 to 5 ft (0.61 to 1.52 m) in diameter and are constructed by individuals. Gorillas, unlike chimpanzees or orangutans, tend to sleep in nests on the ground. The young nest with their mothers, but construct nests after three years of age, initially close to those of their mothers.[45] Gorilla nests are distributed arbitrarily and use of tree species for site and construction appears to be opportunistic.[46] Nest-building by great apes is now considered to be not just animal architecture, but as an important instance of tool use.[46]
Gorillas make a new nest to sleep on each day; even if remaining in the same place, they do not use the previous one. Usually, they are made an hour before dusk, to be ready to sleep when night falls. Gorillas sleep longer than humans, an average of 12 hours per day.[47]
Interspecies interactions
One possible predator of gorillas is the leopard. Gorilla remains have been found in leopard scat, but this may be the result of scavenging.[48] When the group is attacked by humans, leopards, or other gorillas, an individual silverback will protect the group, even at the cost of his own life.[49] Gorillas do not appear to directly compete with chimpanzees in areas where they overlap. When fruit is abundant, gorilla and chimpanzee diets converge, but when fruit is scarce gorillas resort to vegetation.[50] The two apes may also feed on different species, whether fruit or insects.[51][52][53] Gorillas and chimpanzees may ignore or avoid each other when feeding on the same tree,[50][54] but they have also been documented to form social bonds.[55] Conversely, coalitions of chimpanzees have been observed attacking families of gorillas including silverbacks and killing infants.[56]
Gorillas live in groups called troops. Troops tend to be made of one adult male or silverback, with a harem of multiple adult females and their offspring.[57][58][59] However, multiple-male troops also exist.[58] A silverback is typically more than 12 years of age, and is named for the distinctive patch of silver hair on his back, which comes with maturity. Silverbacks have large canine teeth that also come with maturity. Both males and females tend to emigrate from their natal groups. For mountain gorillas, females disperse from their natal troops more than males.[57][60] Mountain gorillas and western lowland gorillas also commonly transfer to second new groups.[57]
Mature males also tend to leave their groups and establish their own troops by attracting emigrating females. However, male mountain gorillas sometimes stay in their natal troops and become subordinate to the silverback. If the silverback dies, these males may be able to become dominant or mate with the females. This behaviour has not been observed in eastern lowland gorillas. In a single male group, when the silverback dies, the females and their offspring disperse and find a new troop.[60][61] Without a silverback to protect them, the infants will likely fall victim to infanticide. Joining a new group is likely to be a tactic against this.[60][62] However, while gorilla troops usually disband after the silverback dies, female eastern lowlands gorillas and their offspring have been recorded staying together until a new silverback transfers into the group. This likely serves as protection from leopards.[61]
Silverback gorilla
The silverback is the centre of the troop’s attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites, and taking responsibility for the safety and well-being of the troop. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years[59] and lack the silver back hair. The bond that a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together.[63] Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males.[64] However, aggressive behaviours between males and females do occur, but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other.[57]
Females may fight for social access to males and a male may intervene.[63] Male gorillas have weak social bonds, particularly in multiple-male groups with apparent dominance hierarchies and strong competition for mates. Males in all-male groups, though, tend to have friendly interactions and socialise through play, grooming, and staying together,[59] and occasionally they even engage in homosexual interactions.[65] Severe aggression is rare in stable groups, but when two mountain gorilla groups meet the two silverbacks can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries.[66]
Reproduction and parenting
Young gorilla riding on mother
Females mature at 10–12 years (earlier in captivity), and males at 11–13 years. A female’s first ovulatory cycle occurs when she is six years of age, and is followed by a two-year period of adolescent infertility.[67] The estrous cycle lasts 30–33 days, with outward ovulation signs subtle compared to those of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four-year interbirth intervals.[67] Males can be fertile before reaching adulthood. Gorillas mate year round.[68]
Females will purse their lips and slowly approach a male while making eye contact. This serves to urge the male to mount her. If the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground.[69] In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males.[69] Males incite copulation by approaching a female and displaying at her or touching her and giving a “train grunt”.[68] Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos.[70]
Mother gorilla with 10-day-old infant
Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival.[62] Male gorillas are not active in caring for the young, but they do play a role in socialising them to other youngsters.[71] The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group.[71] Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection.[71] Infants suckle at least once per hour and sleep with their mothers in the same nest.[72]
Infants begin to break contact with their mothers after five months, but only for a brief period each time. By 12 months old, infants move up to five m (16 ft) from their mothers. At around 18–21 months, the distance between mother and offspring increases and they regularly spend time away from each other.[73] In addition, nursing decreases to once every two hours.[72] Infants spend only half of their time with their mothers by 30 months. They enter their juvenile period at their third year, and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers.[71] After their offspring are weaned, females begin to ovulate and soon become pregnant again.[71][72] The presence of play partners, including the silverback, minimizes conflicts in weaning between mother and offspring.[73]
Twenty-five distinct vocalisations are recognised, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members.[74] They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication.[66]
For this reason, conflicts are most often resolved by displays and other threat behaviours that are intended to intimidate without becoming physical. As a result, fights do not occur very frequently. The ritualized charge display is unique to gorillas. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running, two-legged to four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms to end display.[75]
A gorilla’s chest-beat may vary in frequency depending on its size. Smaller ones tend to have higher frequencies, while larger ones tend to be lower. They also do it the most when females are ready to mate.[76]
A female gorilla exhibiting tool use by using a tree trunk as a support whilst fishing herbs
Gorillas are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Like the other great apes, gorillas can laugh, grieve, have “rich emotional lives”, develop strong family bonds, make and use tools, and think about the past and future.[77] Some researchers believe gorillas have spiritual feelings or religious sentiments.[15] They have been shown to have cultures in different areas revolving around different methods of food preparation, and will show individual colour preferences.[15]
The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means all of the great apes are now known to use tools.[78]
In September 2005, a two-and-a-half-year-old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary.[79] While this was the first such observation for a gorilla, over 40 years previously, chimpanzees had been seen using tools in the wild ‘fishing’ for termites. Nonhuman great apes are endowed with semiprecision grips, and have been able to use both simple tools and even weapons, such as improvising a club from a convenient fallen branch.
Scientific study
American physician and missionary Thomas Staughton Savage obtained the first specimens (the skull and other bones) during his time in Liberia.[8] The first scientific description of gorillas dates back to an article by Savage and the naturalist Jeffries Wyman in 1847 in Proceedings of the Boston Society of Natural History,[80][81] where Troglodytes gorilla is described, now known as the western gorilla. Other species of gorilla were described in the next few years.[5]
Drawing of French explorer Paul Du Chaillu at close quarters with a gorilla
The explorer Paul Du Chaillu was the first westerner to see a live gorilla during his travel through western equatorial Africa from 1856 to 1859. He brought dead specimens to the UK in 1861.[82][83][84]
The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip, he was accompanied by his friends Mary Bradley, a mystery writer, her husband, and their young daughter Alice, who would later write science fiction under the pseudonym James Tiptree Jr. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas, and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.
After World War II, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the mountain gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the mountain gorilla. When she published her work, many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.
The gorilla became the next-to-last great ape genus to have its genome sequenced. The first gorilla genome was generated with short read and Sanger sequencing using DNA from a female western lowland gorilla named Kamilah. This gave scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, 15% of the human genome was found to be more like that of the gorilla.[89] In addition, 30% of the gorilla genome “is closer to human or chimpanzee than the latter are to each other; this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression.”[90] Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans, as it also occurred in gorillas.[91]Several western lowland gorillas in captivity in Japan, 2009
Gorillas became highly prized by western zoos since the 19th century, though the earliest attempts to keep them in captive facilities ended in their early death. In the late 1920s, the care of captive gorillas significantly improved.[92]Colo (December 22, 1956 – January 17, 2017) of the Columbus Zoo and Aquarium was the first gorilla to be born in captivity.[93]
Captive gorillas exhibit stereotypic behaviors, including eating disorders—such as regurgitation, reingestion and coprophagy—self-injurious or conspecific aggression, pacing, rocking, sucking of fingers or lip smacking, and overgrooming.[94] Negative vigilance of visitor behaviors have been identified as starting, posturing and charging at visitors.[95] Groups of bachelor gorillas containing young silverbacks have significantly higher levels of aggression and wounding rates than mixed age and sex groups.[96][97]
The use of both internal and external privacy screens on exhibit windows has been shown to alleviate stresses from visual effects of high crowd densities, leading to decreased stereotypic behaviors in the gorillas.[95] Playing naturalistic auditory stimuli as opposed to classical music, rock music, or no auditory enrichment (which allows for crowd noise, machinery, etc. to be heard) has been noted to reduce stress behavior as well.[98] Enrichment modifications to feed and foraging, where clover-hay is added to an exhibit floor, decrease stereotypic activities while simultaneously increasing positive food-related behaviors.[95]
Recent research on captive gorilla welfare emphasizes a need to shift to individual assessments instead of a one-size-fits-all group approach to understanding how welfare increases or decreases based on a variety of factors.[97] Individual characteristics such as age, sex, personality and individual histories are essential in understanding that stressors will affect each individual gorilla and their welfare differently.[95][97]
All species (and subspecies) of gorilla are listed as endangered or critically endangered on the IUCN Red List.[99][100] All gorillas are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that international export/import of the species, including in parts and derivatives, is regulated.[101] Around 316,000 western lowland gorillas are thought to exist in the wild,[102] 4,000 in zoos, thanks to conservation; eastern lowland gorillas have a population of under 5,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 880 left in the wild and none in zoos.[15][99] Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. Gorillas are closely related to humans, and are susceptible to diseases that humans also get infected by. In 2004, a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus.[103] A 2006 study published in Science concluded more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated in conjunction with commercial hunting of these apes, the virus creates “a recipe for rapid ecological extinction“.[104] In captivity, it has also been observed that gorillas can also be infected with COVID-19.[105]
Drawing of a gorilla who has killed a hunter and destroyed his shotgun, as narrated by Paul Du Chaillu, 1861
In Cameroon’s Lebialem highlands, folk stories connect people and gorillas via totems; a gorilla’s death means the connected person will die also. This creates a local conservation ethic.[107] Many different indigenous peoples interact with wild gorillas.[107] Some have detailed knowledge; the Baka have words to distinguish at least ten types of gorilla individuals, by sex, age, and relationships.[107] In 1861, alongside tales of hunting enormous gorillas, the traveller and anthropologist Paul Du Chaillu reported the Cameroonian story that a pregnant woman who sees a gorilla will give birth to one.[107][108]
In 1911, the anthropologist Albert Jenks noted the Bulu people‘s knowledge of gorilla behaviour and ecology, and their gorilla stories. In one such story, “The Gorilla and the Child”, a gorilla speaks to people, seeking help and trust, and stealing a baby; a man accidentally kills the baby while attacking the gorilla.[107] Even far from where gorillas live, savannah tribes pursue “cult-like worship” of the apes.[107][109] Some beliefs are widespread among indigenous peoples. The Fang name for gorilla is ngi while the Bulu name is njamong; the root ngi means fire, denoting a positive energy. From the Central African Republic to Cameroon and Gabon, stories of reincarnations as gorillas, totems, and transformations similar to those recorded by Du Chaillu are still told in the 21st century.[107]
Since gaining international attention, gorillas have been a recurring element of many aspects of popular culture and media.[110] They were usually portrayed as murderous and aggressive. Inspired by Emmanuel Frémiet‘s Gorilla Carrying off a Woman, gorillas have been depicted kidnapping human women.[111] This theme was used in films such as Ingagi (1930) and most notably King Kong (1933).[112] The comedic play The Gorilla, which debuted in 1925, featured an escaped gorilla taking a woman from her house.[113] Several films would use the “escaped gorilla” trope including The Strange Case of Doctor Rx (1942), The Gorilla Man (1943), Gorilla at Large (1954) and the Disney cartoons The Gorilla Mystery (1930) and Donald Duck and the Gorilla (1944).[114]
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