Gorilla

Gorillas are large, mostly herbivorous great apes that live in the tropical forests of equatorial Africa. The genus Gorilla has two species, the eastern gorilla and the western gorilla, and either four or five subspecies. The DNA of gorillas is highly similar to that of humans, from 96 to 99% depending on what is included. They are the next closest living relatives to humans after the bonobos and chimpanzees.

Gorillas are the largest living primates. Depending on species and sex, they can reach heights between 1.25 and 1.8 m (4 ft 1 in and 5 ft 11 in), weigh between 68 and 227 kg (150 and 500 lb), and have arm spans of up to 2.6 m (8 ft 6 in). They tend to live in troops, and the leader is called a silverback. The eastern gorilla has darker fur than the western gorilla, along with some other minor differences in body shape. In the wild, gorillas tend to live 35–40 years.

Gorillas live in tropical or subtropical forests in Sub-Saharan Africa. Their range covers only a small part of this region, but they live at a wide range of elevations. The mountain gorilla lives in the montane cloud forests of the Albertine Rift and the Virunga Volcanoes, at heights from 2,200 to 4,300 m (7,200 to 14,100 ft). Lowland gorillas live in dense forests and swamps and marshes as low as sea level. Western lowland gorillas live in Central West African countries, while eastern lowland gorillas live in the Democratic Republic of the Congo, near its border with Rwanda.

About 316,000 western gorillas and 5,000 eastern gorillas are thought to live in the wild. Both species are classified as Critically Endangered by the IUCN. All subspecies are also Critically Endangered, except for the mountain gorilla, which is classified as Endangered. Gorillas face many threats, including poaching, habitat destruction, and disease, which threaten the survival of the species. However, conservation efforts have been successful in some areas where they live.

This article is about the genus of great apes. For other uses, see Gorilla (disambiguation). Not to be confused with Guerrilla.

History and etymology

The word gorilla comes from an expedition by Hanno the Navigator (around 500 BC), a Carthaginian explorer who sailed to the west African coast, to the area that later became Sierra Leone. His group met "savage people," most of them women, whose bodies were hairy, and whom their interpreters called Gorillae. It is not known whether these were gorillas, another kind of ape or monkey, or humans. Skins of the women were said to have been kept at Carthage until Rome destroyed the city 350 years later, at the end of the Punic Wars, in 146 BC.

In 1625, Andrew Battel wrote about an animal called Pongo, which he described as tall, with a face like a man's and a body covered in hair. About 150 years later, a writer named Radermacher said that many people thought the large creature described by Buffon was a Chimera. In 1847, the American doctor and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla from specimens found in Liberia. They named it Troglodytes gorilla, using the name then used for the chimpanzee group. The species name came from an Ancient Greek word, Γόριλλαι (gorillai), meaning "name of a tribe of hairy women."

Evolution and classification

The closest relatives of gorillas are the other two Homininae genera, chimpanzees and humans. All of them diverged from a common ancestor about 7 million years ago. Human genes differ from the matching gorilla genes by only 1.6% on average, but there is still a difference in how many copies each gene has.

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. There is now agreement that there are two species, each with two subspecies, and a third subspecies has been claimed in one of them. These species and subspecies developed from a single type of gorilla during the Ice Age, when their forest homes shrank and became cut off from each other. Primatologists continue to study how the different gorilla groups are related. The proposed third subspecies, which does not yet have a trinomen, is the Bwindi population of the mountain gorilla, sometimes called the Bwindi gorilla.

Anatomy and physiology

Gorillas are the largest living primates. Males are about twice as heavy as females, showing differences in size between males and females. Adult males weigh 136 to 227 kg (300 to 500 lb) and stand 1.4 to 1.8 m (4 ft 7 in to 5 ft 11 in) tall. Females weigh 68 to 113 kg (150 to 250 lb) and stand 1.25 to 1.5 m (4 ft 1 in to 4 ft 11 in) tall. A gorilla's arm span is about 170% of its body length, and its intermembral index is 115. The tallest wild gorilla recorded was a 1.95 m (6 ft 5 in) silverback recorded in Kivu, Democratic Republic of the Congo, in 1938. The heaviest wild gorilla recorded weighed 267 kg (589 lb) and came from Ambam, Cameroon. Gust, a western lowland gorilla at the Antwerp Zoo, was 2.20 m (7 ft 3 in) tall, the tallest recorded in captivity. Males in captivity can become overweight and reach up to 310 kg (683 lb).

Males have a tall sagittal crest on top of the skull, and their canine teeth are much larger than females'. Gorillas have 32 teeth, following the cercopithecoid dental formula pattern. Their crowns on the incisors curve inward, and they have a gap, or diastema, to fit the lower canine. The enamel on the lower premolar helps sharpen the upper canine, and the molar cusps are sharply defined. A thick neck comes from tall bones on the cervical vertebrae. Their vertebral formula includes 7 cervicals, 13 thoracics, 4 lumbars, 6 sacrals, and 3 caudals. The thumb is short and not fully opposable. The hallux is shorter in western gorillas than in eastern gorillas. Gorillas usually move by knuckle-walking, a form of locomotion, though they sometimes walk upright for short distances, mostly while carrying food or when defending themselves. A 2018 study of 77 mountain gorillas at Bwindi Impenetrable National Park found they knuckle-walked only 60% of the time, also using their fists, the backs of their hands and feet, and their palms and soles. Studies of handedness have given mixed results. Gorillas have dark skin and pelage that ranges from dull grey to black, and their faces are glabrescent. Females show swellings during oestrus. Gorilla blood does not react to anti-A and anti-B monoclonal antibodies, so it does not fit the human ABO blood group system, where it would indicate type O blood. Gorillas have a somatic number of 2n = 48. They usually live 35 to 40 years, though captive gorillas may live 50 years or more in rare circumstances. Fatou is the oldest known living gorilla at 69 years and 285 days, and the oldest recorded male, Ozoum, lived to 61 years and 24 days.

Distribution and habitat

Gorillas live between 6°30' N and 5°30' S, except for a 900 km (560 mi) gap between the homes of the western and eastern species. Western lowland gorillas live in swamps and rainforests below 1,000 m (3,300 ft) above sea level, across a 709,000 km² (274,000 sq mi) area of western African forest. This area is bordered by the Oubangui, Sanaga, and lower Congo rivers. Eastern lowland gorillas live in lowland and mountain bamboo forests, between 650 and 2,600 m (2,130 to 8,530 ft) high, in an area bordered by the Lualaba, Lindi, and Luama rivers and the eastern Albertine Rift. Cross River gorillas and mountain gorillas live higher up than their relatives. Mountain gorillas can be found as high as 4,000 m (13,000 ft) in the Virunga Mountains and Bwindi Impenetrable Forest.

Gorillas usually live at an average density of 0.5 to 1.5 gorillas per km², though some places have as many as 10.6 or as few as 0.05. They are often found near rivers and at the edges of forests. They like low swamps next to forests, glades, meadows, and open spaces in high forests.

Ecology

A gorilla's day is split between resting and travelling or feeding. Mountain gorillas mostly eat leaves, stems, pith, and shoots, and fruit makes up only a very small part of their diet. Eastern lowland gorillas eat a more varied diet, and fruit can make up as much as 25% of it. Western lowland gorillas depend on fruit more than other gorillas do. Because fruit is harder to find, lowland gorillas must travel farther each day. Gorillas also eat insects, and western lowland gorillas eat termites and ants. Although they are often thought of as ground-dwelling apes, a 2025 study found that gorillas can spend a lot of time in trees, depending on the area. Bwindi Impenetrable National Park and Loango National Park gorillas spend more time climbing trees than gorillas at Virunga.

Gorillas build nests for daytime and night use. Unlike chimpanzees or orangutans, they tend to sleep in nests on the ground. Young gorillas nest with their mothers and start building their own nests after three years of age. A gorilla makes a new nest each day, usually about an hour before dusk. Gorillas sleep an average of 12 hours a day, which is longer than humans. Nest-building by great apes is now considered to be more than animal architecture, and an important example of tool use.

One possible predator of gorillas is the leopard. When a group is attacked by humans, leopards, or other gorillas, an adult male called a silverback will protect the group, even at the cost of his own life. Gorillas and chimpanzees usually do not compete directly where they live together. When fruit is plentiful, their diets are similar, but when fruit is scarce, gorillas eat more vegetation. Sometimes the two apes ignore or avoid each other, and sometimes they form social bonds. However, groups of chimpanzees have also been seen attacking gorilla families, including silverbacks, and killing infants.

Behaviour

Gorillas live in groups called troops. Most troops have one adult male, called a silverback, who is usually over 12 years old. He gets his name from the patch of silver hair on his back that grows as he matures. The silverback makes the decisions, settles conflicts, chooses where the group moves, and protects the troop. Younger males called blackbacks may help protect the group. The bond between a silverback and his females is the core of gorilla social life. Females also form dominance hierarchies among themselves. If a silverback dies, the troop may break up, and infants may be at risk from infanticide.

Females mature at 10–12 years and males at 11–13 years, and gorillas mate throughout the year. A female may show she is ready by pursing her lips and slowly approaching a male. Gorillas have also been seen engaging in face-to-face mating, a behaviour once thought to be unique to humans and bonobos. Mothers are the main caregivers of infants, and the silverback helps protect them. Gorillas use twenty-five different vocalisations to communicate, and screams and roars are used to warn of danger. Conflicts are usually settled with displays rather than fights. The ritualized chest-beating charge display is unique to gorillas.

Intelligence

Further information: Primate cognition

Scientific study

American physician and missionary Thomas Staughton Savage obtained the first specimens, including the skull and other bones, while he was in Liberia. In 1847, Savage and the naturalist Jeffries Wyman published the first scientific description of gorillas from near the river Gaboon, in which they described what is now known as the western gorilla. Other species of gorilla were described over the next few years.

The explorer Paul Du Chaillu was the first westerner to see a live gorilla, during his travels through western equatorial Africa from 1856 to 1859. Later, George Schaller studied the mountain gorilla in the wild, and Dian Fossey conducted a longer and more detailed study of it. Her work helped show that many myths about gorillas were untrue, including the idea that gorillas are violent. Scientists also later mapped the gorilla's genome, which gave them new insight into the evolution and origin of humans.

Captivity

Gorillas were highly prized by western zoos from the 19th century, but the earliest attempts to keep them in captive facilities ended in their early deaths. In the late 1920s, the care of captive gorillas greatly improved. Colo (22 December 1956 – 17 January 2017) of the Columbus Zoo and Aquarium was the first gorilla born in captivity.

Captive gorillas can show stereotypic behaviors, such as eating problems like regurgitation, reingestion and coprophagy, as well as pacing, rocking, sucking fingers, lip smacking, and overgrooming. Groups of young male gorillas have been found to be more aggressive than mixed groups of males and females. Research has shown that privacy screens on exhibit windows, playing natural sounds, and adding clover-hay to the exhibit floor can reduce stress behaviors. Recent research stresses that each gorilla's welfare should be judged individually, because age, sex, personality and past experiences all affect how each gorilla is affected by stress.

Conservation status

An eastern lowland gorilla in the Kahuzi-Biega National Park, Democratic Republic of the Congo

All kinds of gorilla are listed as either endangered or critically endangered on the IUCN Red List. All gorillas are also listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), which means that international trade in gorillas, including their parts, is controlled. In 2016, about 316,000 western lowland gorillas were thought to live in the wild and 4,000 in zoos, thanks to conservation. Eastern lowland gorillas number under 5,000 in the wild and 24 in zoos. Mountain gorillas are the most endangered, with about 880 left in the wild and none in zoos. Threats include habitat destruction and poaching for the bushmeat trade.

Gorillas are closely related to humans, so they can catch some of the same diseases. In 2004, several hundred gorillas in Odzala National Park, Republic of Congo, were almost completely wiped out by the Ebola virus. A 2006 study in Science concluded that more than 5,000 gorillas may have died in recent Ebola outbreaks in central Africa. The researchers said that, along with commercial hunting, the virus creates "a recipe for rapid ecological extinction." Conservation efforts include the Great Apes Survival Project, a partnership between the United Nations Environment Programme and UNESCO, and the Agreement on the Conservation of Gorillas and Their Habitats, an international treaty made under the Convention on Migratory Species. This Gorilla Agreement came into effect in June 2008 and is the first legally binding agreement focused only on gorilla conservation. Governments have banned killing and trading gorillas, but weak law enforcement is still a threat because governments rarely catch poachers, traders, and buyers who profit from them.

Cultural significance

In Cameroon's Lebialem highlands, folk stories link people and gorillas through totems. In these stories, a gorilla's death means that the connected person will also die, which creates a local interest in protecting gorillas. Many indigenous peoples know wild gorillas well. The Baka have words for at least ten kinds of gorilla individuals, based on sex, age, and relationships. In 1861, the traveller and anthropologist Paul Du Chaillu reported a Cameroonian story that a pregnant woman who sees a gorilla will give birth to one. In 1911, the anthropologist Albert Jenks noted the Bulu people's knowledge of gorilla behaviour and their gorilla stories, such as "The Gorilla and the Child," in which a gorilla seeks help and trust from people, then steals a baby. The Fang name for gorilla is ngi, which means fire and stands for a positive energy. Stories of gorillas, reincarnation, and totems are still told in the 21st century from the Central African Republic to Cameroon and Gabon.

Since gorillas gained international attention, they have appeared often in popular culture and media, usually as murderous and aggressive creatures. Inspired by Emmanuel Frémiet's Gorilla Carrying off a Woman, gorillas were shown kidnapping human women in films such as Ingagi (1930) and especially King Kong (1933). Other films and cartoons used the "escaped gorilla" idea, 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). Gorillas have also been opponents of jungle heroes like Tarzan and Sheena, Queen of the Jungle, and of superheroes. The DC Comics villain Gorilla Grodd is an enemy of the Flash. More positive portrayals include Son of Kong (1933), Mighty Joe Young (1949), Gorillas in the Mist (1988), Instinct (1999), and the 1992 novel Ishmael. Gorillas appear in video games too, notably Donkey Kong. In American English, the idiom "800-pound gorilla" describes an entity so powerful that it can act without regard to others' rights or the law, based on a riddle joke:

Q. Where does an 800-pound gorilla sit? A. Anywhere it wants to.

The idea can describe a powerful nation or military, or a business that is so dominant in its market that it can crush competitors. The phrase has sometimes been mixed with the metaphor has been mixed of the elephant in the room.