Gorillas are ground-dwelling, predominantly herbivorous apes that inhabit the forest of central Sub-Saharan Africa. The genus Gorilla is divided into two species: the eastern gorillas and the western gorillas (both critically endangered), and either four or five subspecies. They are the largest living primates. The DNA of gorillas is highly similar to that of humans, from 95 to 99% depending on what is included, and they are the next closest living relatives to humans after the chimpanzees and bonobos.

Gorillas' natural habitats cover tropical or subtropical forest in Sub-Saharan Africa. Although their range covers a small percentage of Sub-Saharan Africa, gorillas cover a wide range of elevations. The mountain gorilla inhabits the Albertine Rift montane cloud forests of the Virunga Volcanoes, ranging in altitude from 2,200 to 4,300 metres (7,200 to 14,100 ft). Lowland gorillas live in dense forests and lowland swamps and marshes as low as sea level, with western lowland gorillas living in Central West African countries and eastern lowland gorillas living in the Democratic Republic of the Congo near its border with Rwanda.


Etymology
The word "gorilla" comes from the history of Hanno the Navigator, (c. 500 BC) a Carthaginian explorer on an expedition on the west African coast to the area that later became Sierra Leone. Members of the expedition encountered "savage people, the greater part of whom were women, whose bodies were hairy, and whom our interpreters called Gorillae". It is unknown whether what the explorers encountered were what we now call gorillas, another species of ape or monkeys, or humans. 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.

The American physician and missionary Thomas Staughton Savage and naturalist Jeffries Wyman first described the western gorilla (they called it Troglodytes gorilla) in 1847 from specimens obtained in Liberia. The name was derived from Ancient Greek Γόριλλαι (gorillai), meaning 'tribe of hairy women', described by Hanno.


Physical characteristics
Gorillas move around by knuckle-walking, although they sometimes walk bipedally for short distances while carrying food or in defensive situations, and some mountain gorillas use other parts of their hand to aid locomotion (studies of 77 mountain gorillas published in 2018 showed 61% only used knuckle walking, but the remainder used knuckle walking plus other parts of their hand—fist walking in ways that do not use the knuckles, using the backs of their hand, and using their palms). There is individual variation in the frequency and ease with which gorillas walk upright; certain gorillas at Philadephia Zoo and London Zoo have been observed walking upright more frequently and for longer distances than normal, with one gorilla at the Philadelphia Zoo often doing so to avoid getting mud on his hands. Wild male gorillas weigh 136 to 227 kg (300 to 500 lb), while adult females weigh 68–113 kg (150–250 lb).

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. Groves (1970) calculated the average weight of 47 wild adult male gorillas at 143 kg, while Smith and Jungers (1997) found the average weight of 19 wild adult male gorillas to be 170 kg. Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. The tallest 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. The heaviest gorilla recorded was a 1.83 m (6 ft 0 in) silverback shot in Ambam, Cameroon, which weighed 267 kg (589 lb). Males in captivity can be overweight and reach weights up to 310 kg (683 lb). 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.

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 grayish 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.

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 ♥♥♥ blood group system, into which the other great apes fit. Like humans, gorillas have individual fingerprints. Their eye colour is dark brown, framed by a black ring around the iris.

A gorilla's lifespan is normally between 35 and 40 years, although zoo gorillas may live for 50 years or more. Colo, a female western gorilla at the Columbus Zoo and Aquarium, was the oldest known gorilla at 60 years of age when she died on 17 January 2017.


Distribution and habitat
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 forest between 650 and 4,000 m (2,130 and 13,120 ft) above sea level. Mountain gorillas live in montane forest at the higher end of the elevation range, while eastern lowland gorillas live in submontane forest at the lower end. In addition, eastern lowland gorillas live in montane bamboo forest, as well as lowland forest ranging from 600–3,308 m (1,969–10,853 ft) in elevation. Western gorillas live in both lowland swamp forest and montane forest, at elevations ranging from sea level to 1,600 m (5,200 ft). Western lowland gorillas live in swamp and lowland forest ranging up to 1,600 m (5,200 ft), and Cross River gorillas live in low-lying and submontane forest ranging from 150–1,600 m (490–5,250 ft).


Nest
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. Gorilla nests are distributed arbitrarily and use of tree species for site and construction appears to be opportunistic. Nest-building by great apes is now considered to be not just animal architecture, but as an important instance of tool use.


Food and foraging
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. 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 (1.16 to 5.79 mi2), and their movements range around 500 m (0.31 mi) or less on an average day. Despite eating a few species in each habitat, mountain gorillas have flexible diets and can live in a variety of habitats.

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%