Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus Gorilla is divided into 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 95 to 99% depending on what is included, and they are the next closest living relatives to humans after chimpanzees and bonobos. Gorillas are the largest living primates, reaching heights between 1.25 and 1.8 metres, weights between 100 and 270 kg, and arm spans up to 2.6 metres, 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. 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.
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. 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. 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). Western gorilla gorilla gorilla and eastern gorilla Gorilla beringei 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. Like humans, gorillas have individual fingerprints. 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. 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. 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. 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. Another gorilla, Ozzie, was 61 years old at the time of his death in January 2022.