Gorilla
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| Gorilla[1] | ||||||||||||||||
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 Western Gorilla (Gorilla gorilla) | ||||||||||||||||
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| Troglodytes gorilla Savage, 1847 | ||||||||||||||||
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 distribution of Gorilla |
Gorillas are the largest of the living primates. They are ground-dwelling and predominantly herbivorous. They inhabit the forests of central Africa. Gorillas are divided into two species and (still under debate as of 2008) either four or five subspecies. The DNA of gorillas is 98%–99% identical to that of a human,[2] and they are the next closest living relatives to humans after the two chimpanzee species.
Gorillas live in tropical or subtropical forests. 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 2225 to 4267 m (7300-14000 ft). Lowland Gorillas live in dense forests and lowland swamps and marshes as low as sea level.
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Etymology
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.[3] The name was derived from the Greek word Gorillai (a "tribe of hairy women") described by Hanno the Navigator, a Carthaginian navigator and possible visitor (circa 480 BC) to the area that later became Sierra Leone.[4]
Evolution and classification
The closest relatives of gorillas are chimpanzees and humans, from which gorillas diverged about 7 million years ago.[5] Human genes differ only 1.6% on average from their corresponding gorilla genes in their sequence, but there is further difference in how many copies each gene has.[6]
Until recently there was considered to be a single gorilla species, with three subspecies: the Western Lowland Gorilla, the Eastern Lowland Gorilla and the Mountain Gorilla.[7][8] There is now agreement that there are two species with two subspecies each. More recently it has been claimed that a third subspecies exists in one of the species.
Primatologists continue to explore the relationships between various gorilla populations.[7] The species and subspecies listed here are the ones upon which most scientists agree.[citation needed]
- Genus Gorilla [1]
- Western Gorilla (Gorilla gorilla)
- Western Lowland Gorilla (Gorilla gorilla gorilla)
- Cross River Gorilla (Gorilla gorilla diehli)
- Eastern Gorilla (Gorilla beringei)
- Mountain Gorilla (Gorilla beringei beringei)
- Eastern Lowland Gorilla (Gorilla beringei graueri)
- Western Gorilla (Gorilla gorilla)
The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the Mountain Gorilla, sometimes called the Bwindi Gorilla.
Physical characteristics
Gorillas move around by knuckle-walking. Adult males range in height from 165-175 cm (5 ft 5 in – 5 ft 9 in), and in weight from 140–204.5 kg (310–450 lb). Adult females are often half the size of a silverback, averaging about 140 cm (4 ft 7 in) tall and 100 kg (220 lb). Occasionally, a silverback of over 183 cm (6 ft) and 225 kg (500 lb) has been recorded in the wild. However, obese gorillas in captivity have reached a weight of 270 kg (600 lb).[9] Gorillas have a facial structure which is described as mandibular prognathism, that is, their mandible protrudes farther out than the maxilla.
The Eastern Gorilla is more darkly colored 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 forests are more slender and agile than the more bulky Mountain Gorilla.[10]
Almost all gorillas share the same blood type (B)[11] and, like humans, have individual finger prints.[12]
Behavior
Group life
A silverback is an adult male gorilla, typically more than 12 years of age and named for the distinctive patch of silver hair on his back. A silverback gorilla has large canine teeth that come with maturity. Blackbacks are sexually mature males of up to 11 years of age.
Silverbacks are the strong, dominant troop leaders. Each typically leads a troop (group size ranges from 5 to 30) and is in the center of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites and taking responsibility for the safety and well-being of the troop. Blackbacks may serve as backup protection.
Males will slowly begin to leave their original troop when they are about 11 years old, traveling alone or with a group of other males for 2–5 years before being able to attract females to form a new group and start breeding. While infant gorillas normally stay with their mother for 3–4 years, silverbacks will care for weaned young orphans, though never to the extent of carrying the little gorillas. If challenged by a younger or even by an outsider male, a silverback will scream, beat his chest, break branches, bare his teeth, then charge forward. Sometimes a younger male in the group can take over leadership from an old male. If the leader is killed by disease, accident, fighting or poachers, the group will split up, as the animals disperse to look for a new protective male. Occasionally, a group may be taken over in its entirety by another male. There is a strong risk that the new male will kill the infants of the dead silverback.
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