Gorillas are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. The eponymous 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 95–99% depending on what is counted, and they are the next closest living relatives to humans after the chimpanzees and bonobos.
Gorillas' natural habitats cover tropical or subtropical forests in Africa. Although their range covers a small percentage of 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 2,200–4,300 metres (7,200–14,100 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.[3]
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.[4] Members of the expedition encountered "savage people, the greater part of whom were women, whose bodies were hairy, and whom our interpreters called Gorillae".[5] The word was then later used as the species name, though it is unknown whether what these ancient Carthaginians encountered were truly gorillas, another species of ape or monkeys, or humans.[6]
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.[7] The name was derived from Ancient Greek Γόριλλαι (gorillai), meaning 'tribe of hairy women',[8] described by Hanno.
Evolution and classification
The closest relatives of gorillas are the other two Homininae species, chimpanzees and humans, all of them having diverged from a common ancestor about 7 million years ago.[9] Human gene sequences differ only 1.6% on average from the sequences of corresponding gorilla genes, but there is further difference in how many copies each gene has.[10] 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.[6][11] There is now agreement that there are two species, each with two subspecies. More recently, a third subspecies has been claimed to exist in one of the species. The separate species and subspecies developed from a single type of gorilla during the Ice Age, when their forest habitats shrank and became isolated from each other.[3]
Conservation status
All species (and sub-species) of gorilla are listed as Critically Endangered on the IUCN Red List.[71] Now, over 100,000 western lowland gorillas are thought to exist in the wild, with 4,000 in zoos; eastern lowland gorillas have a population of under 5,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 880 left in the wild and none in zoos.[3][71] Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. In 2004, a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus.[72] A 2006 study published in Science concluded more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated in conjunction with commercial hunting of these apes, the virus creates "a recipe for rapid ecological extinction".[73] Conservation efforts include the Great Apes Survival Project, a partnership between the United Nations Environment Programme and the UNESCO, and also an international treaty, the Agreement on the Conservation of Gorillas and Their Habitats, concluded under UNEP-administered Convention on Migratory Species. The Gorilla Agreement is the first legally binding instrument exclusively targeting gorilla conservation; it came into effect on 1 June 2008.
Primatologists continue to explore the relationships between various gorilla populations.[6] The species and subspecies listed here are the ones upon which most scientists
Distribution and habitat
Young gorilla in tree
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 forests to swamps. Eastern gorillas inhabit montane and submontane forests between 650 and 4,000 m (2,130 and 13,120 ft) above sea level.[25] Mountain gorillas live in the montane forests at the higher ends of the elevation range, while eastern lowland gorillas live in submontane forests at the lower ends of the elevation range. In addition, eastern lowland gorillas live in montane bamboo forests, as well as lowland forests ranging from 600–3,308 m (1,969–10,853 ft) in elevation.[26] Western gorillas live in both lowland swamp forests and montane forests, and elevations ranging from sea level to 1,600 m (5,200 ft).[25] Western lowland gorillas live in
Reproduction and parenting
Young gorilla riding on mother
Females mature at 10–12 years (earlier in captivity), and males at 11–13 years. A female’s first ovulatory cycle occurs when she is six years of age, and is followed by a two-year period of adolescent infertility.[46] The estrous cycle lasts 30–33 days, with outward ovulation signs subtle compared to those of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four-year interbirth intervals.[46] Males can be fertile before reaching adulthood. Gorillas mate year round.[47]
Females will purse their lips and slowly approach a male while making eye contact. This serves to urge the male to mount her. If the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground.[48] In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males.[48] Males incite copulation by approaching a female and displaying at her or touching her and giving a "train grunt".[47] Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos.[49]
Mother gorilla with 10-day-old infant
Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival.[41] Male gorillas are not active in caring for the young, but they do play a role in socialising them to other youngsters.[50] The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group.[50] Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection.[50] Infants suckle at least once per hour and sleep with their mothers in the same nest.[51]
Infants begin to break contact with their mothers after five months, but only for a brief period each time. By 12 months old, infants move up to five meters (16.4 ft) from their mothers. At around 18–21 months, the distance between mother and offspring increases and they regularly spend time away from each other.[52] In addition, nursing decreases to once every two hours.[51] Infants spend only half of their time with their mothers by 30 months. They enter their juvenile period at their third year, and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers.[50] After their offspring are weaned, females begin to ovulate and soon become pregnant again.[50][51] The presence of play partners, including the silverback, minimizes conflicts in weaning between mother and
