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. Gorillas also have several subspecies. Their DNA is very similar to that of humans. They are the next closest living relatives to humans after the bonobos and chimpanzees.

Gorillas are the largest living primates. Depending on the species and whether they are male or female, they can be up to about 1.8 m (5 ft 11 in) tall and weigh a lot. They usually live in groups called troops, and the leader of each troop is called a silverback. The eastern gorilla has darker fur than the western gorilla. In the wild, gorillas usually live about 35 to 40 years.

Gorillas live in tropical or subtropical forests in Sub-Saharan Africa. They live in only a small part of this region, but they can be found at many different heights. The mountain gorilla lives in misty cloud forests of the Albertine Rift and the Virunga Volcanoes, high up in the mountains. Lowland gorillas live in dense forests, swamps, and marshes, close to sea level. Western lowland gorillas live in countries in Central West Africa. 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 Critically Endangered, which means they are in very great danger of disappearing. All subspecies are also Critically Endangered, except the mountain gorilla, which is Endangered. Gorillas face threats such as hunting, the loss of their forest homes, and disease. However, conservation efforts have helped gorillas 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 a trip by Hanno the Navigator around 500 BC. He was a Carthaginian explorer who sailed along the west African coast, to the area that later became Sierra Leone. His group met hairy people, most of them women, whom their interpreters called Gorillae. No one knows whether these were gorillas, another kind of ape or monkey, or humans. About 350 years later, Rome destroyed the city of Carthage at the end of the Punic Wars, in 146 BC.

In 1625, Andrew Battel wrote about an animal called Pongo. He described it 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 comes 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 three diverged from a common ancestor about 7 million years ago. Human genes are very similar to matching gorilla genes, differing by only 1.6% on average. However, humans and gorillas still differ in how many copies of each gene they have.

Until recently, gorillas were thought to be one species with three subspecies: the western lowland gorilla, the eastern lowland gorilla, and the mountain gorilla. Scientists now agree there are two species, and each has two subspecies. A third subspecies has been proposed in one of them. These species and subspecies developed from one type of gorilla during the Ice Age, when their forest homes became smaller and separated from each other. Primatologists are still studying how the different gorilla groups are related. The proposed third subspecies does not yet have a trinomen. It 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. 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 arms stretch 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 found 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 gorilla 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' teeth. Gorillas have 32 teeth, following the cercopithecoid dental formula pattern. The crowns of their incisors curve inward, and there is a gap, or diastema, that fits 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 in the cervical vertebrae. Their vertebral formula includes 7 cervical, 13 thoracic, 4 lumbar, 6 sacral, and 3 caudal vertebrae. 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. Sometimes they 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 that they knuckle-walked only 60% of the time. They also used 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 (fur) that ranges from dull grey to black, and their faces are glabrescent, meaning they have little hair. 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 show type O blood. Gorillas have a somatic number of 2n = 48.

Gorillas usually live 35 to 40 years. Captive gorillas may live 50 years or more in rare circumstances. Fatou is the oldest known living gorilla, at 69 years and 285 days old. The oldest recorded male, Ozoum, lived to 61 years and 24 days.

Distribution and habitat

Gorillas live in a band of land close to the equator. There is a large gap of about 900 km (560 mi) between the homes of the western and eastern kinds of gorillas. Western lowland gorillas live in swamps and rainforests below 1,000 m (3,300 ft) above sea level. They live across a large area of western African forest. This area is bordered by the Oubangui, Sanaga, and lower Congo rivers. Eastern lowland gorillas live in forests with bamboo, both on lower ground and in the mountains. They live between 650 and 2,600 m (2,130 to 8,530 ft) high. Their area is 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. Some places have more gorillas, and some have far fewer. 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 spends its day resting, moving around, and eating. Mountain gorillas mostly eat leaves, stems, pith, and shoots. Fruit makes up only a very small part of their food. Eastern lowland gorillas eat a more varied diet, and fruit can make up as much as 25% of it. Western lowland gorillas eat more fruit than other gorillas do. Because fruit is harder to find, lowland gorillas must travel farther each day. Gorillas also eat insects. Western lowland gorillas eat termites and ants. Gorillas are often thought of as ground-dwelling apes, but a 2025 study found that they can spend a lot of time in trees, depending on where they live. Gorillas in Bwindi Impenetrable National Park and Loango National Park spend more time climbing trees than gorillas in Virunga.

Gorillas build nests to rest in during the day and at night. Unlike chimpanzees or orangutans, they usually sleep in nests on the ground. Young gorillas nest with their mothers. They start building their own nests after about three years of age. A gorilla builds a new nest each day, usually about an hour before dusk. Gorillas sleep about 12 hours a day, which is longer than humans do. Scientists now think that nest-building by great apes is more than animal architecture. It is an important example of tool use.

One possible predator of gorillas is the leopard. When a group is threatened by humans, leopards, or other gorillas, an adult male called a silverback will protect the group, even if it puts his own safety at risk. Gorillas and chimpanzees usually do not compete directly where they live together. When fruit is plentiful, their diets are similar. When fruit is scarce, gorillas eat more plants. Sometimes the two apes ignore or avoid each other, and sometimes they form friendly bonds. However, chimpanzees have also been seen attacking gorilla families.

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 gets older. The silverback makes the decisions, settles disagreements, chooses where the group goes, and protects the troop. Younger males called blackbacks may also help protect the group. The bond between a silverback and his females is the center of gorilla family life. Females also form dominance hierarchies among themselves. If a silverback dies, the troop may break apart, and infants may be at risk from infanticide.

Females grow up at 10–12 years and males at 11–13 years. Gorillas can mate at any time of year. A female may show she is ready by pursing her lips and slowly approaching a male. Scientists have also seen gorillas mating face to face, 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. 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 collected the first gorilla specimens, including the skull and some 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. They described what is now known as the western gorilla. Other kinds 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 Africa from 1856 to 1859. Later, George Schaller studied the mountain gorilla in the wild, and Dian Fossey carried out 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 always violent. Scientists also later mapped the gorilla's genome, which helped them learn more about how humans evolved.

Captivity

Gorillas were very popular with zoos in Western countries starting in the 1800s. Many of the first gorillas kept in zoos died young. In the late 1920s, people became much better at caring for captive gorillas. Colo (22 December 1956 – 17 January 2017) lived at the Columbus Zoo and Aquarium. He was the first gorilla born in captivity.

Gorillas kept in captivity can develop stereotypic behaviors. These are repeated actions that have no clear purpose. They include eating problems such as regurgitation, reingestion and coprophagy. They also include pacing, rocking, sucking fingers, lip smacking, and overgrooming. Groups of young male gorillas were 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 floor can reduce stress behaviors. Newer research says that each gorilla's welfare should be judged on its own. Age, sex, personality and past experiences all affect how much stress a gorilla feels.

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). This means that trade in gorillas, including their body parts, is controlled. In 2016, about 316,000 western lowland gorillas were thought to live in the wild, and about 4,000 lived in zoos. Eastern lowland gorillas number fewer than 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. Gorillas face threats from habitat destruction and from poaching for the bushmeat trade.

Gorillas are closely related to humans, so they can catch some of the same diseases. In 2004, a disease called Ebola virus spread through gorillas in Odzala National Park, in the Republic of Congo, and killed many of them. A 2006 study in Science found that Ebola outbreaks in central Africa may have killed many gorillas in recent years. The researchers said that, along with 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. There is also 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. It is the first legal agreement focused only on gorilla conservation. Governments have banned killing and trading gorillas. However, weak law enforcement is still a problem, because governments rarely catch the poachers, traders, and buyers who profit from them.

Cultural significance

In the Lebialem highlands of Cameroon, folk stories link people and gorillas through totems. In these stories, if a gorilla dies, the person connected to it will also die. This makes local people want to protect gorillas. Many indigenous peoples know wild gorillas well. The Baka have words for at least ten kinds of gorillas, based on sex, age, and relationships. In 1861, the traveller and anthropologist Paul Du Chaillu wrote down a Cameroonian story that says a pregnant woman who sees a gorilla will give birth to one. In 1911, the anthropologist Albert Jenks wrote about the Bulu people's knowledge of gorilla behaviour and their gorilla stories. One story, "The Gorilla and the Child," tells of a gorilla that seeks help and trust from people, then takes a baby. The Fang name for gorilla is ngi, which means fire and stands for a positive energy. Stories about gorillas, reincarnation, and totems are still told today in the Central African Republic, Cameroon, and Gabon.

Since people around the world became interested in gorillas, they have often appeared in popular culture and media. They were usually shown as dangerous and aggressive creatures. Inspired by Emmanuel Frémiet's Gorilla Carrying off a Woman, films such as Ingagi (1930) and especially King Kong (1933) showed gorillas carrying people away. Other films and cartoons used the idea of an "escaped gorilla," 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 enemies 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. Some films show gorillas in a more positive way, including Son of Kong (1933), Mighty Joe Young (1949), Gorillas in the Mist (1988), Instinct (1999), and the 1992 novel Ishmael. Gorillas also appear in video games, especially Donkey Kong. In American English, the idiom "800-pound gorilla" describes a powerful thing that can act without caring about others' rights or the law. It comes from 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 strong in its market that it can crush its competitors. The phrase has sometimes been mixed with the metaphor has been mixed of the elephant in the room.