Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||32||Public Records:||10|
|Specimens with Sequences:||31||Public Species:||2|
|Specimens with Barcodes:||30||Public BINs:||1|
|Species With Barcodes:||2|
Gorillas comprise the eponymous genus Gorilla, the largest extant genus of primates by size. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. The genus is divided into two species and either four or five subspecies. The DNA of gorillas is highly similar to that of a human, from 95–99% depending on what is counted, and they are the next closest living relatives to humans after the bonobo and common chimpanzee.
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.
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 Greek Γόριλλαι (Gorillai), meaning "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.
Evolution and classification
The closest relatives of gorillas are chimpanzees and humans, all of the Hominidae having diverged from a common ancestor about 7 million years ago. 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. 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. There is now agreement that there are two species with two subspecies each. 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.
|Taxonomy of genus Gorilla||Phylogeny of superfamily Hominoidea(Fig. 4)|
Some variations that distinguish the classifications of gorilla include varying density, size, hair color, length, culture, and facial widths. 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 4,000 in the wild and 24 in zoos. Mountain gorillas are the most severely endangered, with an estimated population of about 620 left in the wild and none in zoos.
Gorillas move around by knuckle-walking, although they sometimes walk bipedally for short distances while carrying food or in defensive situations. Wild male gorillas weigh 135 to 180 kg (300 to 400 lb) while adult females usually weigh half as much as adult males at 68–113 kg (150–250 lb). Adult males are 1.7 to 1.8 m (5.6 to 5.9 ft) tall, with an arm span that stretches from 2.3 to 2.6 m (7.5 to 8.5 ft). Female gorillas are shorter with smaller arm spans. Adult male gorillas are known as silverbacks due to characteristic silver hair on their backs reaching to the hips. Occasionally, a silverback of over 1.8 metres (5 ft 11 in) and 230 kg (510 lb) has been recorded in the wild. Obese gorillas in captivity can weigh as much as 270 kg (600 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 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 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 ABO blood group system, into which the other great apes fit. Like humans, gorillas have individual finger prints. Their eye color is dark brown, framed by a black ring around the iris. Similar to humans, the leading cause of death in gorillas is cardiovascular disease.
Behavior and ecology
Range 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 forests to swamps. Eastern gorillas inhabit montane and submontane forests between 650 and 4000 m (2132-13,123 ft) above sea level. 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 600–3308 m (1969-10,853 ft) in elevation. Western gorillas live in both lowland swamp forests and montane forests, and elevations ranging from sea level to 1600 m (5249 ft). Western lowland gorillas live in swamp and lowland forests ranging up to 1600 m (5249 ft), and Cross River gorillas live in low-lying and submontane forests ranging from 150–1600 m (492–5249 ft).
Food and foraging
A gorilla's day is synchronized, 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 both individuals and groups do not have to compete with each other. Their home ranges average 3–15 km2 (1.16–5.79 mi2), and their movements range around 500 m (0.311 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% of their diets. Since fruit is less available, lowland gorillas must travel farther each day, and their home ranges vary from 2.7–6.5 km2 (1.04 to 2.51 mi2), with day ranges 154–2280 m (0.096–1.42 mi). Eastern lowland gorillas will also eat insects, preferably ants. Western lowland gorillas depend on fruits more than the others and they are more dispersed across their range. They travel even further than the other gorilla subspecies, at 1105 m (0.687 mi) per day on average, and have larger home ranges of 7–14 km2 (2.70–5.41 mi2). Western lowland gorillas have less access to terrestrial herbs, although they can access aquatic herbs in some areas. Termites and ants are also eaten.
Gorillas rarely drink water "because they consume succulent vegetation that is comprised of almost half water as well as morning dew", although both mountain and lowland gorillas have been observed drinking.
One possible predator of gorillas is the leopard. Gorilla remains have been found in leopard scat, but this may be the result of scavenging. When the group is attacked by humans, leopards, or other gorillas, an individual silverback will protect the group, even at the cost of his own life. George Schaller reported, "[a] silverback gorilla and a leopard were both found dead from mutually inflicted wounds".
Gorillas live in groups called troops. Troops tend to be made of one adult male or silverback, multiple adult females and their offspring. However, multiple-male troops also exist. A silverback is typically more than 12 years of age, and is named for the distinctive patch of silver hair on its back, which comes with maturity. Silverbacks also have large canine teeth which also come with maturity. Both males and females tend to emigrate from their natal groups. For mountain gorillas, females disperse from their natal troops more than males. Mountain gorillas and western lowland gorillas also commonly transfer to second new groups. Mature males tend to also leave their groups and establish their own troops by attracting emigrating females. However, male mountain gorillas sometimes stay in their natal troops and become subordinate to the silverback. If the silverback dies, these males may be able to become dominant or mate with the females. This behavior has not been observed in eastern lowland gorillas. In a single male group, when the silverback dies, the females and their offspring disperse and find a new troop. Without a silverback to protect them, the infants will likely fall victim to infanticide. Joining a new group is likely to be a tactic against this. However, while gorilla troops usually disband after the silverback dies, female eastern lowlands gorillas and their offspring have been recorded staying together until a new silverback transfers into the group. This likely serves as protection from leopards. All-male troops have also been recorded.
The silverback is 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. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years of age and lack the silver back hair. The bond a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together. Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. However, aggressive behaviors between males and females do occur, but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other. Females may fight for social access to males and a male may intervene. Male gorillas have weak social bonds, particularly in multiple-male groups with apparent dominance hierarchies and strong competition for mates. Males in all-male groups, though, tend to have friendly interactions and socialize through play, grooming and staying together, and occasionally they even engage in homosexual interactions.
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 1.5 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.
Reproduction and parenting
Females mature at 10–12 years (earlier in captivity); 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. The estrous cycle last 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. Males can be fertile before reaching adulthood. Gorillas mate year round.
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. In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males. Males incite copulation by approaching a female and displaying at her or touching her and giving a "train grunt". Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos.
Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival. Male gorillas are not active in caring for the young, but they do play a role in socializing them to other youngsters. The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group. Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection. Infants will suckle at least once per hour and will sleep with their mothers in the same nest.
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. In addition, nursing decreases to once every two hours. 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. After their offspring are weaned, females begin to ovulate and soon become pregnant again. The presence of play partners, including the silverback, minimize conflicts in weaning between mother and offspring.
A gorilla's lifespan is between 35 and 40 years, although zoo gorillas may live for 50 years and more. Dallas Zoo's Jenny was the oldest living gorilla in captivity until 2008, when she died at the age of 55. Now it is Colo - on 22 December 2011 she celebrated her 55th birthday at the Columbus Zoo and Aquarium.
Twenty-five distinct vocalizations are recognized, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while traveling, and indicate the whereabouts of individual group members. They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning, and are produced most often by silverbacks. Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication. Severe aggression is rare in stable groups, but when two mountain gorilla groups meet, the two silverbacks can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries.
For this reason, conflicts are most often resolved by displays and other threat behaviors that are intended to intimidate without becoming physical. The ritualized charge display is unique to gorillas. The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running, two-legged to four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms to end display.
Gorillas are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Like the other great apes, gorillas can laugh, grieve, have "rich emotional lives", develop strong family bonds, make and use tools, and think about the past and future. Some researchers believe gorillas have spiritual feelings or religious sentiments. They have been shown to have cultures in different areas revolving around different methods of food preparation, and will show individual color preferences.
The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means all of the great apes are now known to use tools.
In September 2005, a two-and-a-half-year-old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary. While this was the first such observation for a gorilla, over 40 years previously, chimpanzees had been seen using tools in the wild 'fishing' for termites. Great apes are endowed with semiprecision grips, and have been able to use both simple tools and even weapons, by improvising a club from a convenient fallen branch, for example.
Interactions with humans
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. They encountered "a savage people, the greater part of whom were women, whose bodies were hairy, and who our interpreters called Gorillae". 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.
American physician and missionary Thomas Staughton Savage obtained the first specimens (the skull and other bones) during his time in Liberia in Africa. The first scientific description of gorillas dates back to an article by Savage and the naturalist Jeffries Wyman in 1847 in Proceedings of the Boston Society of Natural History, where Troglodytes gorilla is described, now known as the western gorilla. Other species of gorilla are described in the next few years.
The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip, he was accompanied by his friends Mary Bradley, a mystery writer, her husband, and their young daughter Alice, who would later write science fiction under the pseudonym James Tiptree Jr. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas, and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.
After World War II, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the mountain gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the mountain gorilla. When she published her work, many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.
Western lowland gorillas (Gorilla gorilla gorilla) are believed to be one of the zoonotic origins of HIV/AIDS. The SIVgor Simian immunodeficiency virus that infects them is similar to a certain strain of HIV-1.
The eastern gorilla is listed as endangered on the IUCN Red List, with the mountain gorilla listed as Critically Endangered. The western gorilla and its subspecies are also listed as Critically Endangered. 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. 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." 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.
The gorilla became the next-to-last great ape genus to have its genome sequenced. This has given scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, 15% of the human genome was found to be more like that of the gorilla. In addition, 30% of the gorilla genome "is closer to human or chimpanzee than the latter are to each other; this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression." Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans, as it also occurred in gorillas.
Since they came to the attention of western society in the 1860s, gorillas have been a recurring element of many aspects of popular culture and media. For example, gorillas have featured prominently in monstrous fantasy films such as King Kong, and pulp fiction such as the stories of Tarzan and Conan the Barbarian have featured gorillas as physical opponents to the titular protagonists.
- Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. pp. 181–182. OCLC 62265494. ISBN 0-801-88221-4.
- Prince-Hughes, Dawn (1987). Songs of the Gorilla Nation. Harmony. p. 66. ISBN 1-4000-5058-8.
- Conniff R. Discovering gorilla. Evolutionary Anthropology, 18: 55–61. doi:10.1002/evan.20203
- Γόριλλαι, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
- Müller, C. (1855–61). Geographici Graeci Minores. pp. 1.1–14: text and trans. Ed, J. Blomqvist (1979).
- Glazko GV, Nei M (March 2003). "Estimation of divergence times for major lineages of primate species". Mol. Biol. Evol. 20 (3): 424–34. doi:10.1093/molbev/msg050. PMID 12644563.
- Goidts V, Armengol L, Schempp W et al. (March 2006). "Identification of large-scale human-specific copy number differences by inter-species array comparative genomic hybridization". Hum. Genet. 119 (1–2): 185–98. doi:10.1007/s00439-005-0130-9. PMID 16395594.
- Groves, Colin (2002). "A history of gorilla taxonomy". Gorilla Biology: A Multidisciplinary Perspective, Andrea B. Taylor & Michele L. Goldsmith (editors) (Cambridge University Press): 15–34. doi:10.2277/0521792819.
- Stewart, Kelly J.; Pascale Sicotte, Martha M. Robbins (2001). "Mountain Gorillas of the Virungas". Fathom / Cambridge University Press. Retrieved 2008-09-11.
- Israfil, H.; Zehr, S. M.; Mootnick, A. R.; Ruvolo, M.; Steiper, M. E. (2011). "Unresolved molecular phylogenies of gibbons and siamangs (Family: Hylobatidae) based on mitochondrial, Y-linked, and X-linked loci indicate a rapid Miocene radiation or sudden vicariance event" (PDF). Molecular Phylogenetics and Evolution 58 (3): 447–455. doi:10.1016/j.ympev.2010.11.005. PMC 3046308. PMID 21074627.
- Prince-Hughes, Dawn (1987). Songs of the Gorilla Nation. Harmony. pp. 82–3. ISBN 1-4000-5058-8.
- Miller, Patricia (1997). Gorillas. p. 64. ISBN 0919879896.
- "Gorilla – The Columbia Encyclopedia, Sixth Edition". bartleby.com. Archived from the original on 2008-02-12. Retrieved 2006-10-10.
- Rowe N. (1996) Pictorial guide to the living primates. East Hampton (NY): Pogonias Pr.
- Gamble, K. C.; Moyse, J. A.; Lovstad, J. N.; Ober, C. B.; Thompson, E. E. (2011). "Blood groups in the Species Survival Plan, European Endangered Species Program, and managed in situ populations of bonobo (Pan paniscus), common chimpanzee (Pan troglodytes), gorilla (Gorilla ssp.), and orangutan (Pongo pygmaeus ssp.)" (pdf). Zoo Biology 30 (4): 427–444. doi:10.1002/zoo.20348. PMID 20853409. Retrieved 5 January 2012.
- "Santa Barbara Zoo – Western Lowland Gorilla". santabarbarazoo.org. Retrieved 2006-10-10.
- Gorrilas. Smithonian National Zoological Park
- Palmer, Jane. "How does a gorilla get a physical? Carefully". Retrieved 03/08/2007.
- Sarmiento EE. (2003) "Distribution, taxonomy, genetics, ecology, and causal links of gorilla survival: the need to develop practical knowledge for gorilla conservation". In: Taylor AB, Goldsmith ML, editors. Gorilla biology: a multidisciplinary perspective. Cambridge (England): Cambridge Univ Pr. pp. 432–71.
- Ilambu O. (2001) "Ecology of Eastern Lowland gorilla: is there enough scientific knowledge to mitigate conservation threats associated with extreme disturbances in its distribution range?" In: The apes: challenges for the 21st century. Conference proceedings; 2000 May 10–13; Brookfield, IL. Chicago: Chicago Zoo Soc. pp. 307–12.
- McNeilage A. (2001) "Diet and habitat use of two mountain gorilla groups in contrasting habitats in the Virungas". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge University Press. pp. 265–92.
- Yamagiwa J, Mwanza N, Yumoto T, Maruhashi T. (1994). "Seasonal change in the composition of the diet of eastern lowland gorillas". Primates 35: 1. doi:10.1007/BF02381481.
- Tutin CG. (1996) "Ranging and social structure of lowland gorillas in the Lopé Reserve, Gabon". In: McGrew WC, Marchant LF, Nishida T, editors. Great ape societies. Cambridge (England): Cambridge Univ Press pp. 58–70.
- GORILLAS – Diet & Eating Habits. Seaworld.org. Retrieved on 2011-09-27.
- Fay JM, Carroll R, Kerbis Peterhans JC, Harris D. (1995). "Leopard attack on and consumption of gorillas in the Central African Republic". Journal of Human Evolution 29 (1): 93–9. doi:10.1006/jhev.1995.1048.
- Wildlife: Mountain Gorilla. AWF. Retrieved on 2011-09-27.
- Making a Last Stand Counterattack and Chutzpah Living Primates. Intechinc.com (2011-08-19). Retrieved on 2011-09-27.
- Watts DP. (1996) "Comparative socio-ecology of gorillas". In: McGrew WC, Marchant LF, Nishida T, editors. Great ape societies. Cambridge (England): Cambridge Univ Pr. p 16-28.
- Yamagiwa J, Kahekwa J, Kanyunyi Basabose A. (2003). "Intra-specific variation in social organization of gorillas: implications for their social evolution". Primates 44 (4): 359–69. doi:10.1007/s10329-003-0049-5. PMID 12942370.
- Robbins MM. (2001) "Variation in the social system of mountain gorillas: the male perspective". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 29–58.
- Stokes EJ, Parnell RJ, Olejniczak C. (2003). "Female dispersal and reproductive success in wild western lowland gorillas (Gorilla gorilla gorilla)". Behav Ecol Sociobiol 54 (4): 329–39. doi:10.1007/s00265-003-0630-3. JSTOR 25063274.
- Yamagiwa J, Kahekwa J. (2001) "Dispersal patterns, group structure, and reproductive parameters of eastern lowland gorillas at Kahuzi in the absence of infanticide". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 89–122.
- Watts DP. (1989). "Infanticide in mountain gorillas: new cases and a reconsideration of the evidence". Ethology 81: 1–18. doi:10.1111/j.1439-0310.1989.tb00754.x.
- Watts DP. (2003) "Gorilla social relationships: a comparative review". In: Taylor AB, Goldsmith ML, editors. Gorilla biology: a multidisciplinary perspective. Cambridge (England): Cambridge Univ Pr. pp. 302–27.
- Watts DP. (2001) "Social relationships of female mountain gorillas". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 216–40.
- Juichi Yamagiwa (1987). "Intra- and Inter-group Interactions of an All-male Group of Virunga Mountain Gorillas (Gorilla gorilla beringei )". Primates 28 (1): 1–30. doi:10.1007/BF02382180.
- Miller-Schroeder, Patricia (1997). Gorillas. Weigl Educational Publishers. p. 20. ISBN 978-0-919879-89-8. Retrieved 4 July 2011.
- Marchant, Linda Frances; Nishida, Toshisada (1996). Great ape societies. Cambridge University Press. pp. 226–227. ISBN 978-0-521-55536-4. Retrieved 4 July 2011.
- Czekala N, Robbins MM. (2001) "Assessment of reproduction and stress through hormone analysis in gorillas". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 317–39.
- Watts DP (1991). "Mountain gorilla reproduction and sexual behavior". Am J Primatol 24 (3–4): 211. doi:10.1002/ajp.1350240307.
- Sicotte P. (2001) "Female mate choice in mountain gorillas". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 59–87.
- Tuan C. Nguyen. "Caught in the act! Gorillas mate face to face". MSN.
- Stewart KJ. (2001) "Social relationships of immature gorillas and silverbacks". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge Univ Pr. pp. 183–213.
- Stewart KJ (1988). "Suckling and lactational anoestrus in wild gorillas (Gorilla gorilla)". J Reprod Fertil 83 (2): 627–34. doi:10.1530/jrf.0.0830627. PMID 3411555.
- Fletcher A. (2001) "Development of infant independence from the mother in wild mountain gorillas". In: Robbins MM, Sicotte P, Stewart KJ, editors. Mountain gorillas: three decades of research at Karisoke. Cambridge (England): Cambridge University Press. pp. 153–82.
- World's oldest gorilla celebrates 55th birthday. 3news.co.nz. 9 May 2009
- Gorilla celebrates 55th birthday with frozen cake. Gmanews.tv. Retrieved on 2011-09-27.
- Associated Press, Oldest living gorilla dies at 55. 6 September 2008.
- Wilson, J. (16 December 2011). "Colo Queen Of The Columbus Zoo Celebrates Year 55". Columbus Zoo & Aquarium. Retrieved 10 February 2012.
- Harcourt, A.H., Stewart, K.J., Hauser, M. (1993). "Functions of wild gorilla 'close' calls. I. Repertoire, context, and interspecific comparison". Behaviour 124: 89. doi:10.1163/156853993X00524.
- Fossey, D. (1983). Gorillas in the mist. Boston: Houghton Mifflin Company. ISBN 0-395-28217-9.
- Maple, T.L., & Hoff, M.P. (1982). Gorilla Behavior. New York: Van Nostrand Reinhold Company.
- Planet Of No Apes? Experts Warn It's Close CBS News Online, 2007-09-12. Retrieved 2008-03-22.
- Breuer T, Ndoundou-Hockemba M, Fishlock V (2005). "First Observation of Tool Use in Wild Gorillas". PLoS Biol 3 (11): e380. doi:10.1371/journal.pbio.0030380. PMC 1236726. PMID 16187795.
- "A Tough Nut To Crack For Evolution". CBS News. 2005-10-18. Retrieved 2006-10-18.
- Periplus of Hanno, final paragraph. Shsu.edu. Retrieved on 2011-09-27.
- Savage TS. (1847). Communication describing the external character and habits of a new species of Troglodytes (T. gorilla). Boston Soc Nat Hist, pp. 245–247.
- Savage TS, Wyman J. (1847). Notice of the external characters and habits of Troglodytes gorilla, a new species of orang from the Gaboon River, osteology of the same. Boston J Nat Hist 5:417–443.
- McCook, S. (1996). ""It May Be Truth, but It Is Not Evidence": Paul du Chaillu and the Legitimation of Evidence in the Field Sciences". Osiris 11: 177–197. doi:10.1086/368759.
- A History of Museum Victoria: Melbourne 1865: Gorillas at the Museum. Museumvictoria.com.au. Retrieved on 2011-09-27.
- Quammen, David (April 4, 2013). "Book Review: Planet of the Ape - ‘Between Man and Beast,’ by Monte Reel". New York Times. Retrieved April 6, 2013.
- Van Heuverswyn, Fran; Li, Yingying; Neel, Cecile; Bailes, Elizabeth; Keele, Brandon F.; Liu, Weimin; Loul, Severin; Butel, Christelle et al. (2006). "Human immunodeficiency viruses: SIV infection in wild gorillas". Nature 444 (7116): 164. Bibcode:2006Natur.444..164V. doi:10.1038/444164a. PMID 17093443.
- Plantier, Jean-Christophe; Leoz, Marie; Dickerson, Jonathan E; De Oliveira, Fabienne; Cordonnier, François; Lemée, VéRonique; Damond, Florence; Robertson, David L et al. (2009). "A new human immunodeficiency virus derived from gorillas". Nature Medicine 15 (8): 871–72. doi:10.1038/nm.2016. PMID 19648927.
- Sharp, P. M.; Bailes, E.; Chaudhuri, R. R.; Rodenburg, C. M.; Santiago, M. O.; Hahn, B. H. (2001). "The origins of acquired immune deficiency syndrome viruses: where and when?". Philosophical Transactions of the Royal Society B: Biological Sciences 356 (1410): 867–76. doi:10.1098/rstb.2001.0863. PMC 1088480. PMID 11405934.
- Takebe, Y; Uenishi, R; Li, X (2008). "Global Molecular Epidemiology of HIV: Understanding the Genesis of AIDS Pandemic". HIV-1: Molecular Biology and Pathogenesis. Advances in Pharmacology 56. pp. 1–25. doi:10.1016/S1054-3589(07)56001-1. ISBN 9780123736017.
- Robbins, M. & Williamson, L. (2008). Gorilla gorilla. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2012.
- Robbins, M., Gray, M., Kümpel, N., Lanjouw, A., Maisels, F., Mugisha, A., Spelman, L. & Williamson, L. (2008). Gorilla gorilla. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2012.
- Walsh, P. D., Tutin, C. E. G., Oates, J. F., Baillie, J. E. M., Maisels, F., Stokes, E. J., Gatti, S., Bergl, R. A., Sunderland-Groves, J. & Dunn, A. (2008). Gorilla gorilla. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 January 2012.
- "Gorillas infecting each other with Ebola". NewScientist.com. 2006-07-10. Retrieved 2006-07-10.
- "Ebola 'kills over 5,000 gorillas'". News.bbc.co.uk. 2006-12-08. Retrieved 2006-12-09.
- Kate Kelland (7 March 2012). "Gorilla genome sheds new light on human evolution". Reuters. Retrieved 8 March 2012.
- Aylwyn Scally, et al. (2012). "Insights into hominid evolution from the gorilla genome sequence". Nature 483 (7388): 169–175. doi:10.1038/nature10842. PMC 3303130. PMID 22398555.
- Kerri Smith (7 March 2012). "Gorilla joins the genome club". Nature News.
To request an improvement, please leave a comment on the page. Thank you!