General · EdgepediaSeptember 17, 20268 min read

Gorilla

Gorillas (genus Gorilla) are the largest living primates, ground-dwelling plant-eating great apes native to the forests of equatorial Africa. Two species are currently recognized on the basis of morphology and geographic distribution: the western gorilla (Gorilla gorilla) in the tropical forests north of the Congo River, and the eastern gorilla (Gorilla beringei) roughly 1,000 km to the east, extending to the slopes of the central African mountains¹. Each species is divided into two subspecies: western lowland gorillas (G. g. gorilla) and Cross River gorillas (G. g. diehli) in the west, and mountain gorillas (G. b. beringei) and Grauer's gorillas (G. b. graueri) in the east².

Key fact	Detail
Species and subspecies	Western gorilla (G. gorilla: western lowland, Cross River) and eastern gorilla (G. beringei: mountain, Grauer's), separated by a gap of several hundred kilometers¹^•²
Size	Males up to 5.7 ft (1.75 m) and 300 to 400 lb (136 to 181 kg); females up to 5 ft (1.5 m) and 159 to 216 lb (72 to 98 kg)²
Divergence	Average sequence divergence between the western and eastern species about 1.75 million years ago, with evidence of more recent genetic exchange and a population bottleneck in the eastern species³
Genetic diversity	Western gorillas are more diverse genome-wide; eastern lowland gorillas appear to be the most inbred gorilla population, with both recent and ancient inbreeding⁴
Conservation	Eastern gorilla listed as Critically Endangered in 2016; mountain gorilla downlisted to Endangered in November 2018 after its population exceeded 1,000⁵^•⁶
Numbers	The western lowland subspecies may number up to 200,000 individuals; the eastern population as a whole is around ten times smaller³
Reproduction	A female gives birth to one baby every four to six years and only three or four over her lifetime⁷

Taxonomy and distribution

The two-species classification is a recent development. Until recently the eastern and western populations were considered subspecies of a single species, and the first detailed study of gorilla taxonomy, published by Groves in 1970, recognized one species with three subspecies⁸. Studies of geographic variation in DNA, skulls, and teeth led to the recognition of two species, and the 2021 IUCN Red List distinguishes four subspecies⁹^•⁸.

The contemporary distribution features a pronounced gap of several hundred kilometers between the two species, which nonetheless retain behavioral and morphological similarities¹⁰. Western gorilla populations reside primarily in Cameroon, Equatorial Guinea, Gabon, Congo, and the Central African Republic, while eastern gorilla populations occur in lowlands and highlands in the Democratic Republic of Congo, Uganda, and Rwanda¹¹. The northwestern limit of the western lowland subspecies is the Sanaga River in Cameroon¹².

Evolutionary history

Genomic studies have reconstructed a complex split between the two species. One analysis of neutral autosomal loci proposed a scenario in which a single ancestral gorilla population persisted until 0.9 to 1.6 million years ago, followed by reduced, possibly male-mediated gene flow until a population split around 77,700 years ago¹³. The gorilla genome paper estimated an average sequence divergence time of 1.75 million years between the species but found evidence of more recent genetic exchange³. A later comparative analysis of 53 resequenced genomes, using a mutation rate of 1.8 × 10⁻⁹ per generation and a 20-year generation time, estimated that gene flow between the two species stopped circa 150,000 to 180,000 years ago¹⁴.

Gene flow was a recurring theme. A Y-chromosome study genotyping 257 wild male gorillas from all four subspecies found 102 unique Y-haplotypes and concluded that male-mediated gene flow may have been important in the past¹⁵. A 2023 analysis reported admixture from a possible unsampled "ghost" population in eastern gorillas, and the comparative genome study detected multiple signals of introgression between subspecies, suggesting gene flow was likely common throughout gorilla evolution¹⁶^•¹⁴.

Genetic diversity is unevenly distributed. Western lowland gorillas show the highest variation, best explained by larger present and past effective population sizes and higher rates of gene flow through largely continuous habitat¹⁷. Eastern lowland gorillas appear to represent the most inbred population, with evidence of both recent and ancient inbreeding⁴. Despite population decline, gorillas maintain an overall level of genetic diversity equal to or greater than that of humans¹.

Physical characteristics, diet, and ecology

With their heavily built bodies, wide chests and shoulders, big hands resembling those of humans, and small eyes in faces lacking hair, gorillas have a distinctive appearance.⁷ They can stand upright but prefer to walk on all fours using the backs of their fingers, a gait called knuckle walking, and their arms are much longer than their legs². Captive life-span averages 33 years for males and 39 years for females².

Almost everything a gorilla eats is plant material: leaves, stems, fruits, seeds, and roots, supplemented with ants and termites². An adult male eats up to 40 pounds (18 kilograms) of food each day². Field studies indicate the western gorilla diet comprises as many as 230 plant parts from 180 plant species¹¹. Gorillas play a key role in their forests: their fibrous scat acts as rich fertilizer and seedlings sprout from it rapidly, and by spreading seeds and opening gaps in the canopy they help sun-loving plants grow²^•⁷.

Social organization and life history

A group of gorillas is called a troop, typically of 5 to 30 animals, led by a dominant adult male known as a silverback for the silver hair he develops with age²^•¹⁸. The silverback makes decisions about daily travel, feeding, and resting sites, and builds each night's nest; gorillas never use the same nest twice².

Social organization varies markedly between the species. Western gorilla groups are almost exclusively one-male, yet approximately 40% of mountain gorilla groups are multimale. A review by Martha M. Robbins and colleagues at the Max Planck Institute for Evolutionary Anthropology identified five ultimate causes for this variability: human disturbance, ecological constraints on group size, risk of infanticide, life history patterns, and population density, with the most evidence for the ecological constraints and life history hypotheses¹⁹.

Reproduction is slow. Females become sexually mature around seven or eight years old but do not begin breeding until a couple of years later; once breeding, a female gives birth to one baby every four to six years and only three or four in her lifetime⁷. Gestation lasts 8 to 9 months, newborns weigh 4 to 5 pounds (1.8 to 2.3 kg), and females reach maturity at about 8 years, males at about 13². This low reproductive rate makes it difficult for gorilla populations to recover from declines⁷.

Conservation

Both gorilla species are listed as endangered or critically endangered. The eastern gorilla, the largest living primate, was listed as Critically Endangered in 2016 due to illegal hunting⁵. Grauer's gorilla lost 77% of its population since 1994, declining from 16,900 individuals to just 3,800 in 2015⁵. The western gorilla is also listed as Critically Endangered²⁰.

Mountain gorillas are the exception. A 2018 survey put the global mountain gorilla population above 1,000, a significant recovery for a subspecies that once faced possible extinction, and the IUCN downlisted it from Critically Endangered to Endangered in November 2018²¹^•⁶. Mountain gorilla habitat remains restricted to protected areas covering approximately 792 km² in two locations, the Virunga Massif and Bwindi-Sarambwe⁶.

Threats include poaching, habitat destruction and fragmentation, civil unrest, and disease. Scientists in 2003 estimated that a third of the wild gorilla population had been killed by the Ebola virus, which is deadly to both gorillas and humans⁷. Because of their genetic similarity to people, gorillas are susceptible to human pathogens, and almost 60% of the remaining mountain gorillas are habituated to humans, coming into close contact with people daily²². Only about 22% of western lowland gorillas live in protected areas, leaving most of the subspecies vulnerable to poachers⁷. Unselective hunting with snares set for other wildlife, such as antelopes and bush pigs, often kills or injures gorillas²³.

Conservation responses include gorilla tourism, which has turned poachers into conservationists in Uganda while generating economic benefits for local communities, and reforestation around Bwindi, where communities have planted trees for medicine, firewood, and crafts to reduce pressure on the park²⁴^•²¹. The International Gorilla Conservation Programme, a coalition of WWF, Conservation International, and Fauna & Flora, has contributed to the mountain gorilla recovery⁷.

References

Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026