Chimpanzee

Evolution

Despite a large number of Homo fossil finds, Pan fossils were not described until 2005. Existing chimpanzee populations in West and Central Africa do not overlap with the major human fossil sites in East Africa, but chimpanzee fossils have now been reported from Kenya. This indicates that both humans and members of the Pan clade were present in the East African Rift Valley during the Middle Pleistocene.^[1][20][21]

Evolutionary biologists and paleontologists have attempted to reconstruct the last common ancestor of Homo and Pan (CHLCA). By the end of the 20th century, it was assumed that humans evolved from a chimpanzee-like ancestor. A 2015 study of Ardipithecus, an early human relative dated 4.4 mya, disputed this interpretation. The study concluded that humans, chimpanzees and bonobos evolved from a generalised species that lacked the derived traits of both genera.^[22] Subsequent studies disputed this, finding that the hand of Ardipithecus was adapted for suspension climbing and the heel for vertical climbing, much like modern African apes.^[23][24] Anthropologist Alice Roberts indicates that at least 24 species of hominin have appeared after the divergence of humans from chimpanzees estimated at 10 to 7 million years ago.^[25] When describing the extinct species Sahelanthropus in 2002, Brunet et al. noted the combination of ancient features not expressed in chimpanzees that would be considered archaic or derived for a species on the human line (the subtribe Hominina), the latter being bipedal locomotion and reduced canine teeth, which they interpreted as evidence of its position near the chimpanzee–human last common ancestor (CHLCA). For example, in addition to the study of Ardipithecus in studying traits expressed and not expressed in chimpanzees, researchers such as M. Burnet have examined Sahelanthropus, the oldest Hominina, shifting the centre of origin for the clade away from East Africa and CHLCA origins. They also suggested that Sahelanthropus could be a sister group to the 5.5-to-4.5-million-year-old Ardipithecus and later Hominina after the separation from the chimpanzee line.^[26]

According to studies published in 2017 by researchers at George Washington University, bonobos, along with chimpanzees, split from the human line about 8 million years ago; then bonobos split from the common chimpanzee line about 2 million years ago.^[27][28] Another 2017 genetic study suggests ancient gene flow (introgression) between 200,000 and 550,000 years ago from the bonobo into the ancestors of central and eastern chimpanzees.^[29] Roberts states that the examination of DNA in close relatives of chimpanzees, humans and gorillas makes note that they have a common ancestor in the orangutan with each differing in their own genetic composition by 3.1% from the orangutan. The comparable difference in DNA between the chimpanzee and the gorilla is 1.6% difference, and between chimpanzees and humans is 1.2% difference.^[30]

Subspecies and population status

Four subspecies of the chimpanzee have been recognised,^[31][32] with the possibility of a fifth:^[29][33]

• Central chimpanzee or the tschego (Pan troglodytes troglodytes), found in Cameroon, the Central African Republic, Equatorial Guinea, Gabon, the Republic of the Congo, and the Democratic Republic of the Congo, with about 140,000 individuals existing in the wild.^[34]
• Western chimpanzee (P. troglodytes verus), found in Ivory Coast, Guinea, Liberia, Mali, Sierra Leone, Guinea-Bissau, Senegal, and Ghana with about 52,800 individuals still in existence.^[35][36]
• Nigeria-Cameroon chimpanzee (P. troglodytes ellioti (also known as P. t. vellerosus)),^[31] that live within forested areas across Nigeria and Cameroon, with 6,000–9,000 individuals still in existence.^[37][38]
• Eastern chimpanzee (P. troglodytes schweinfurthii), found in the Central African Republic, South Sudan, the Democratic Republic of the Congo, Uganda, Rwanda, Burundi, Tanzania, and Zambia, with approximately 180,000–256,000 individuals still existing in the wild.^[39]
• Southeastern chimpanzee, P. troglodytes marungensis, in Burundi, Rwanda, Tanzania, and Uganda. Colin Groves argues that this is a subspecies, created by enough variation between the northern and southern populations of P. t. schweinfurthii,^[33] but it is not recognised by the IUCN.^[2]

Genome

A draft of the chimpanzee genome was first published in 2005 and found that almost 99% of the species DNA sequences were shared with humans, along with roughly 30% of proteins.^[40][41] They differ in the number of chromosome pairs, with chimpanzees having 24 and humans 23; this is due to a fusion in two chromosomes during human evolution, producing human chromosome 2.^[42] A 2006 study concluded that around 6% of the genes in chimpanzees and humans differ in the number of copies, creating the majority of evolutionary differences between the two species.^[43] In addition, a 2012 study comparing brain tissue found that chimpanzees and humans diverged significantly in gene regulation, particularly in the activating and de-activating of genes.^[44] A more complete chimpanzee genome was published in 2025. Reading entire chromosomes as opposed to specific sections, the paper concluded that while chimpanzee and human DNA differ by only 1.2% in genetic code sequences, when looking at entire DNA strands—including insertions, deletions and non-coding material—the differences increase up to almost 15%. These differences are primarily in genes related to the brain, immune system and aging.^[45]

Diet

The chimpanzee primarily eats fruit, but also consumes leaves, seeds, blossoms, stems, pith, bark, and resin.^[71][72] A study in Budongo Forest, Uganda concentrate the majority of their feeding time (64.5%) on fruits (84.6% of which being ripe), particularly those from two species of Ficus, Maesopsis eminii, and Celtis gomphophylla. In addition, 19% of feeding time was spent on arboreal leaves, mostly Broussonetia papyrifera and Celtis mildbraedii.^[73] The consummation of woody material like bark appears to have a supplemental or medicinal function rather than just an alternative food source during scarcity.^[74] Seeds and unripe fruits are recorded as important source of food in savanna habitat.^[75] While the chimpanzee is mostly herbivorous, it does eat honey, soil, insects, birds and their eggs, and small to medium-sized mammals, including other primates.^[76][77] Insect species consumed include the weaver ant species Oecophylla longinoda, termites of the genus Macrotermes, and honey bees.^[78][79]

Mammal prey include monkeys like the Western red colobus, the king colobus and baboons, non-simian primates like galagos, rodents like squirrels and hooved mammals like bushpigs, blue duikers, sunis and bushbuck fawns.^[80][81] The red colobus is the most common prey,^[82] though Jane Goodall documented many occasions within Gombe Stream National Park of chimpanzees and western red colobus monkeys ignoring each other despite close proximity.^[69] Meat makes up a small portion of their diet, and does not appear to be a high-quality food source since females—who need the energy they can get when pregnant and nursing young—eat far less of it than males. Nevertheless, it is suggested to have some importance in providing nutrients that help in brain development. Chimpanzees are more likely to hunt when fruit is more abundant, since more individuals aggregate during this time and hunting requires large groups.^[83]

Chimpanzees do not appear to directly compete with gorillas in areas where they overlap. When fruit is abundant, gorillas and chimpanzees both consume it, but when fruit is scarce gorillas switch to eating vegetation.^[84] In addition, gorillas are not as adept at using tools to feed on insects as chimpanzees.^[78] The two apes may also feed on different species, whether fruit or insects.^[78][79][85] Interactions between them can range from friendly and even stable social bonding,^[86] to avoidance,^[84][87] to aggression and even predation of infants on the part of chimpanzees.^[88]

Mortality and health

A 2017 study of the Ngogo community in Kibale National Park found that, when environmental conditions are favourable, chimpanzees live an average life expectancy of nearly 33 years, which is within the expectancy of human hunter gatherers (27–37 years). By contrast, the Kanyawara chimpanzees, which also live in Kibale, have an average life expectancy of 20 years. The life expectancy of chimpanzees at Gombe and Taï average 18 and 13 years respectively. Wild chimpanzees can possibly live for over 60 years.^[89] The oldest-known male captive chimpanzee to have been documented lived to 66 years,^[90] and the oldest female, Little Mama, was nearly 80 years old.^[91]

Leopards prey on chimpanzees in some areas.^[92][93] It is possible that much of the mortality caused by leopards can be attributed to individuals that have specialised in killing chimpanzees.^[92] Chimpanzees may react to a leopard's presence with loud vocalising, vegetation shaking, throwing objects and climbing up trees.^[92][94] There is at least one record of chimpanzees killing a leopard cub after harassing it and its mother in their den.^[95] Four chimpanzees could have fallen prey to lions at Mahale Mountains National Park. Although no other instances of lion predation on chimpanzees have been recorded, lions likely do kill chimpanzees occasionally, and the larger group sizes of savanna chimpanzees may have developed as a response to threats from these big cats. Chimpanzees may react to lions by fleeing up trees, vocalising, or hiding in silence.^[96]

Less than half the parasite and microbe species that infest chimpanzees also infest humans, who show much more overlap more with omnivorous, savanna-dwelling baboons. The chimpanzee is host to the louse species Pediculus schaeffi, a close relative of P. humanus, which lives in human head and body hair. By contrast, the human pubic louse Pthirus pubis is closely related to Pthirus gorillae, which infests gorillas.^[97] A 2017 study of gastrointestinal parasites of wild chimpanzees in degraded forest in Uganda found nine species of protozoa, five nematodes, one cestode, and one trematode. The most prevalent species was the protozoan Troglodytella abrassarti.^[98] In studying the relation of relative hairlessness in humans in comparison to chimpanzees in relation to infection by lice, Eugene Harris has stated that: "Humans, unlike chimpanzees and gorillas, can be infected by two species of body lice. Besides the species that can infect the hair of the head and body, there are lice that specifically infect the more isolated pubic region. The species of head/body lice that infects humans is more closely related to chimpanzee lice. The chimpanzee louse and human head/body louse made their evolutionary split near the same time that humans and chimpanzees went their separate ways (five to six million years ago)."^[99]

Group structure

Chimpanzees live in communities that typically range from around 15 to more than 150 members but spend most of their time traveling in small, temporary groups consisting of a few individuals. These groups may consist of any combination of age and sexes. Both males and females sometimes travel alone.^[69] This fission–fusion society may include groups of four types: all-male, adult females and offspring, adults of both sexes, or one female and her offspring. These smaller groups emerge in a variety of types, for a variety of purposes. For example, an all-male troop may be organised to hunt for meat, while a group consisting of lactating females serves to act as a "nursery group" for the young.^[102] At the core of social structures are males, which patrol the territory, protect group members, and search for food. Males remain in their natal communities, while females generally emigrate at adolescence. Males in a community are more likely to be related to one another than females are to each other. Among males, there is generally a dominance hierarchy, and males are dominant over females.^[103] However, this unusual fission-fusion social structure, "in which portions of the parent group may on a regular basis separate from and then rejoin the rest",^[104] is highly variable in terms of which particular individual chimpanzees congregate at a given time. This is caused mainly by the large measure of individual autonomy that individuals have within their fission-fusion social groups.^[47] As a result, individual chimpanzees often forage for food alone, or in smaller groups, as opposed to the much larger "parent" group, which encompasses all the chimpanzees which regularly come into contact with each other and congregate into parties in a particular area.^[102]

Male chimpanzees exist in a linear dominance hierarchy. Top-ranking males tend to be aggressive even during dominance stability.^[105] This is probably due to the chimpanzee's fission-fusion society, with male chimpanzees leaving groups and returning after extended periods of time. With this, a dominant male is unsure if any changes have occurred in his absence and must re-establish his dominance. Thus, a large amount of aggression occurs within five to fifteen minutes after a reunion. During these encounters, displays of aggression are generally preferred over physical attacks.^[105][106] Males maintain and improve their social ranks by forming coalitions, which have been characterised as "exploitative" and based on an individual's influence in agonistic interactions.^[107] Being in a coalition allows males to dominate a third individual when they could not by themselves, as politically apt chimpanzees can exert power over aggressive interactions regardless of their rank. Coalitions can also give an individual male the confidence to challenge a dominant or larger male. The more allies a male has, the better his chance of becoming dominant. However, most changes in hierarchical rank are caused by dyadic interactions.^[105][108] Chimpanzee alliances can be very fickle, and one member may suddenly turn on another if it is to his advantage.^[109]

Low-ranking males frequently switch sides in disputes between more dominant individuals. Low-ranking males benefit from an unstable hierarchy and often find increased sexual opportunities if a dispute or conflict occurs.^[107][109] In addition, conflicts between dominant males cause them to focus on each other rather than the lower-ranking males. Social hierarchies among adult females tend to be weaker. Nevertheless, the status of an adult female may be important for her offspring.^[110] Females in Taï have also been recorded to form alliances.^[111] While chimpanzee social structure is often referred to as patriarchal, it is not entirely unheard of for females to forge coalitions against males.^[112] There is also at least one recorded case of females securing a dominant position over males in their respective troop, albeit in a captive environment.^[113] Social grooming appears to be important in the formation and maintenance of coalitions. It is more common among adult males than either between adult females or between males and females.^[108]

Chimpanzees have been described as highly territorial and will frequently kill other chimpanzees,^[114] although Margaret Power wrote in her 1991 book The Egalitarians that the field studies from which the aggressive data came, Gombe and Mahale, used artificial feeding systems that increased aggression in the chimpanzee populations studied. Thus, the behaviour may not reflect innate characteristics of the species as a whole.^[115] In the years following her artificial feeding conditions at Gombe, Jane Goodall described groups of male chimpanzees patrolling the borders of their territory, brutally attacking chimpanzees that had split off from the Gombe group. A study published in 2010 found that the chimpanzees wage wars over territory, not mates.^[116] Patrols from smaller groups are more likely to avoid contact with their neighbours. Patrols from large groups even take over a smaller group's territory, gaining access to more resources, food, and females.^[109][117] While it was traditionally accepted that only female chimpanzees immigrate and males remain in their natal troop for life, there are confirmed cases of adult males safely integrating themselves into new communities among West African chimpanzees, suggesting they are less territorial than other subspecies.^[118] West African chimpanzee males are also less aggressive with female chimpanzees in general.^[119] While chimpanzees are popularly thought of as more war-like than bonobos, primatologist Christine Webb concludes that "Through an analysis of various chimpanzee and bonobo sanctuary communities, we've found that variation within the two species is greater than differences between them".^[120]

Mating and parenting

Chimpanzees mate throughout the year, although the number of females in oestrus varies seasonally in a group.^[121] Female chimpanzees are more likely to come into oestrus when food is readily available. Oestrous females exhibit sexual swellings. Chimpanzees are promiscuous; during oestrus, females mate with several males in their community, while males have large testicles for sperm competition. Other forms of mating also exist. A community's dominant males sometimes restrict reproductive access to females. A male and female can form a consortship and mate outside their community. In addition, females sometimes leave their community and mate with males from neighboring communities.^[122][123] These alternative mating strategies give females more mating opportunities without losing the support of the males in their community.^[123] Infanticide has been recorded in chimpanzee communities in some areas, and the victims are often consumed. Male chimpanzees practice infanticide on unrelated young to shorten the interbirth intervals in the females.^[124][125] Females sometimes practice infanticide. This may be related to the dominance hierarchy in females or may simply be pathological.^[110]

Inbreeding was studied in a relatively undisturbed eastern chimpanzee community that displayed substantial bisexual philopatry.^[126] Despite an increased inbreeding risk incurred by females who do not disperse before reaching reproductive age, these females were still able to avoid producing inbred offspring.^[126] Copulation is brief, lasting approximately seven seconds.^[127] The gestation period is eight months.^[47] Care for the young is provided mostly by their mothers. The survival and emotional health of the young is dependent on maternal care. Mothers provide their young with food, warmth, and protection, and teach them certain skills. In addition, a chimpanzee's future rank may be dependent on its mother's status.^[128][129] Male chimpanzees continue to associate with the females they impregnated and interact with and support their offspring.^[130] Orphaned chimpanzees are occasionally adopted by adult males who will be "as protective as any mother" and tend to their needs.^[131]

Newborn chimpanzees are helpless. For example, their grasping reflex is not strong enough to support them for more than a few seconds. For their first 30 days, infants cling to their mother's bellies. Infants are unable to support their own weight for their first two months and need their mothers' support.^[132] Wild chimps are seen to exhibit both "secure" and "insecure" attachment styles, with the offspring looking to the mother for comfort in the former and more independent offspring in the latter. However, wild chimps rarely demonstrate "disorganised" attachment styles (maladaptive parent-offspring bonds caused by abuse or neglect); researchers note such attachment styles are mostly observed in captive chimps raised around humans.^[133]

When they reach five to six months, infants ride on their mothers' backs. They remain in continual contact for the rest of their first year. When they reach two years of age, they are able to move and sit independently and start moving beyond the arms' reach of their mothers. By four to six years, chimpanzees are weaned and infancy ends. The juvenile period for chimpanzees lasts from their sixth to ninth years. Juveniles remain close to their mothers but increasingly begin to interact with other members of their community. Adolescent females move between groups and are supported by their mothers in agonistic encounters. Adolescent males spend time with adult males in social activities like hunting and patrolling the boundaries of their territory.^[132] A captive study suggests males can safely immigrate to a new group if accompanied by immigrant females who have an existing relationship with this male. This gives the resident males reproductive advantages with these females, as they are more inclined to remain in the group if their male friend is also accepted.^[134]

Communication

Pant-hoot call

Pant-hoot call made by an adult male, demonstrating the introduction, build-up, climax, and let-down phases.^[135]

---

Problems playing this file? See media help.

Chimpanzees use facial expressions, postures, and sounds to communicate with each other. They have expressive faces that are important in close-up communications. When frightened, a "full closed grin" causes nearby individuals to be fearful, as well. Playful chimpanzees display an open-mouthed "smile". Chimpanzees may also express themselves with the "pout", which is made in distress, the "sneer", which is made when threatening or fearful, and "compressed-lips face", which is a type of display. When submitting to a dominant individual, a chimpanzee crunches, bobs, and reaches its hand out When in an aggressive mode, a chimpanzee swaggers bipedally, hunched over and arms waving, in an attempt to exaggerate its size.^[136] While travelling, chimpanzees keep in contact by beating their hands and feet against the trunks of large trees, an act that is known as "drumming". They also do this when encountering individuals from other communities.^[137]

Vocalisations are also important in chimpanzee communication. The most common call in adults is the "pant-hoot", which may signal social rank and bond along with keeping groups together. Pant-hoots are made of four parts, starting with soft "hoos", the introduction; that gets louder and louder, the build-up; and climax into screams and sometimes barks; these die down back to soft "hoos" during the letdown phase as the call ends.^[135][137] Grunting is made in situations like feeding and greeting.^[137] Submissive individuals make "pant-grunts" towards their superiors.^[110][138] Whimpering is made by young chimpanzees as a form of begging or when lost from the group.^[137] Chimpanzees use distance calls to draw attention to danger, food sources, or other community members.^[139] "Barks" may be made as "short barks" when hunting and "tonal barks" when sighting large snakes.^[137]

Hunting

When hunting small monkeys such as the red colobus, chimpanzees hunt where the forest canopy is interrupted or irregular. This allows them to easily corner the monkeys when chasing them in the appropriate direction. Chimpanzees may also hunt as a coordinated team, so that they can corner their prey even in a continuous canopy. During an arboreal hunt, each chimpanzee in the hunting groups has a role. "Drivers" serve to keep the prey running in a certain direction and follow them without attempting to make a catch. "Blockers" are stationed at the bottom of the trees and climb up to block prey that takes off in a different direction. "Chasers" move quickly and try to make a catch. Finally, "ambushers" hide and rush out when a monkey nears.^[140] While both adults and infants are taken, adult male colobus monkeys will attack the hunting chimps.^[141] When caught and killed, the meal is distributed to all hunting party members and even bystanders.^[140]

Male chimpanzees hunt in groups more than females. Female chimpanzees tend to hunt solitarily. If a female chimpanzee were to participate in the hunting group and catch a red colobus, it would likely immediately be taken by an adult male. Female chimpanzees are estimated to hunt ≈ 10-15% of a community's vertebrates.^[142]

Tool use

Nearly all chimpanzee populations have been recorded using tools. They modify sticks, rocks, grass, and leaves and use them when foraging for termites and ants, nuts,^{[159][160][161][162]} honey,^[163] algae^[164] or water. Despite their rudimentary and simple quality, forethought and skill are apparent in making these tools.^[145] Chimpanzees have used stone tools since at least 4,300 years ago.^[165]

A chimpanzee from the Kasakela chimpanzee community was the first nonhuman animal reported making a tool, by modifying a twig to use as an instrument for extracting termites from their mound.^[166][167] At Taï, chimpanzees simply use their hands to extract termites.^[145] When foraging for honey, chimpanzees use modified short sticks to scoop the honey out of the hive if the bees are stingless. For hives of the dangerous African honeybees, chimpanzees use longer and thinner sticks to extract the honey.^[168] Chimpanzees also fish for ants using the same tactic.^[169] Ant dipping is difficult and some chimpanzees never master it. West African chimpanzees crack open hard nuts with stones or branches.^[145][169] Some forethought in this activity is apparent, as these tools are not found together or where the nuts are collected. Nut cracking is also difficult and must be learned.^[169] Chimpanzees also use leaves as sponges or spoons to drink water.^[170]

West African chimpanzees in Senegal were found to sharpen sticks with their teeth, which were then used to spear Senegal bushbabies out of small holes in trees.^[171] An eastern chimpanzee has been observed using a modified branch as a tool to capture a squirrel.^[172] Chimpanzees living in Tanzania were found to deliberately choose plants that provide materials that produce more flexible tools for termite fishing.^[173] In 2020, experimental studies on captive chimpanzees have found that many of their species-typical tool-use behaviour can be individually learnt by individual chimpanzees.^[174] However, in comparing hypothesized early hominid making and use of stone flakes, a 2021 study on chimpanzee abilities to make and use stone flakes did not find this behaviour across two populations of chimpanzees—suggesting that this behaviour is outside the chimpanzee species-typical range.^[175]

Speech and language

Scientists have attempted to teach human language to several species of great ape. One early attempt by Allen and Beatrix Gardner in the 1960s involved spending 51 months teaching American Sign Language to a chimpanzee named Washoe. The Gardners reported that Washoe learned 151 signs, and had spontaneously taught them to other chimpanzees, including her adopted son, Loulis.^[176] Over a longer period of time, Washoe was reported to have learned over 350 signs.^[177]

Debate is ongoing among scientists such as David Premack about chimpanzees' ability to learn language. Since the early reports on Washoe, numerous other studies have been conducted, with varying levels of success.^[178] One involved a chimpanzee jokingly named Nim Chimpsky (in allusion to the theorist of language Noam Chomsky), trained by Herbert Terrace of Columbia University. Although his initial reports were quite positive, in November 1979, Terrace and his team, including psycholinguist Thomas Bever, re-evaluated the videotapes of Nim with his trainers, analyzing them frame by frame for signs, as well as for exact context (what was happening both before and after Nim's signs). In the reanalysis, Terrace and Bever concluded that Nim's utterances could be explained merely as prompting on the part of the experimenters, as well as mistakes in reporting the data. "Much of the apes' behaviour is pure drill", he said. "Language still stands as an important definition of the human species". In this reversal, Terrace now argued Nim's use of ASL was not like human language acquisition. Nim never initiated conversations himself, rarely introduced new words, and mostly imitated what the humans did. More importantly, Nim's word strings varied in their ordering, suggesting that he was incapable of syntax. Nim's sentences also did not grow in length, unlike human children whose vocabulary and sentence length show a strong positive correlation.^[179] Chomsky has voiced opposition to the viewpoint of Terrace and Bever based upon his theory of the inheritance of language capacity as being limited to human inheritance alone among all animals.^[180]

In culture and entertainment

The Gio people of Liberia and the Hemba people of the Congo make chimpanzee masks. Gio masks are relatively primitive, and worn when warning young people about bad behaviours. The Hemba masks have a smile perceived as disturbing, and are worn at funerals to represent the "awful reality of death". The masks may also decorate homes for protection and promote fertility, for both humans and plants. Stories have been told of chimpanzees kidnapping and raping women.^[181]

In Western popular culture, chimpanzees have occasionally been stereotyped as childlike companions, sidekicks or clowns. They are especially suited for the latter role on account of their prominent facial features, long limbs and fast movements, which humans often find amusing. Chimpanzees in media include Judy on the television series Daktari in the 1960s and Darwin on The Wild Thornberrys in the 1990s. In contrast to the fictional depictions of other animals, such as dogs (as in Lassie), dolphins (Flipper), horses (Black Beauty) or even other great apes (King Kong), chimpanzee characters and actions are rarely relevant to the plot. Depictions of chimpanzees as individuals rather than stock characters, and as central rather than incidental to the plot can be found in science fiction. Robert A. Heinlein's 1947 short story "Jerry Was a Man" concerns a genetically enhanced chimpanzee suing for better treatment. The 1972 film Conquest of the Planet of the Apes, the third sequel of the 1968 film Planet of the Apes, portrays a futuristic revolt of enslaved apes led by the only talking chimpanzee, Caesar, against their human masters.^[182]

Entertainment acts featuring chimpanzees dressed up as humans with lip-synchronised human voices have been traditional staples of circuses, stage shows and TV shows like Lancelot Link, Secret Chimp (1970–1972) and The Chimp Channel (1999).^[182] From 1926 until 1972, London Zoo, followed by several other zoos around the world, held a chimpanzees' tea party daily.^[183][184] Animal rights groups have urged a stop to such acts, considering them abusive.^[185]

Domestic pets and dangers

Chimpanzees have traditionally been kept as pets in a few African villages, especially in the Democratic Republic of Congo. In Virunga National Park in the east of the country, the park authorities regularly seize chimpanzees from people keeping them as pets.^[186] Outside their range, chimpanzees are popular as exotic pets despite their strength and aggression. Even in places where keeping non-human primates as pets is illegal, the exotic pet trade continues to prosper, leading to injuries from attacks.^[187]

Chimpanzees have attacked humans.^[188][189] In Uganda, several attacks on children have happened, some of them fatal. Some of these attacks may have been due to the chimpanzees being intoxicated (from alcohol obtained from rural brewing operations) and becoming aggressive towards humans.^[190] Human interactions with chimpanzees may be especially dangerous if the chimpanzees perceive humans as potential rivals.^[191] At least six cases of chimpanzees snatching and eating human babies are documented.^[192]

A chimpanzee's strength and sharp teeth mean that attacks, even on adult humans, can cause severe injuries. This was evident after the attack and near death of former NASCAR driver St. James Davis, who was mauled by two escaped chimpanzees while he and his wife were celebrating the birthday of their former pet chimpanzee.^[193][194] Another example of chimpanzees being aggressive toward humans occurred in 2009 in Stamford, Connecticut, when a 90-kilogram (200 lb), 13-year-old pet chimpanzee named Travis attacked his owner's friend, who lost her hands, eyes, nose, and part of her maxilla from the attack.^[195][196]

Use in research

Hundreds of chimpanzees have been kept in laboratories for research. Most such laboratories either conduct or make the animals available for invasive research,^[197] defined as "inoculation with an infectious agent, surgery or biopsy conducted for the sake of research and not for the sake of the chimpanzee, and/or drug testing".^[198] Research chimpanzees tend to be used repeatedly over decades for up to 40 years, unlike the pattern of use of most laboratory animals.^[199] Two federally funded American laboratories use chimpanzees: the Yerkes National Primate Research Center at Emory University in Atlanta, Georgia, and the Southwest National Primate Center in San Antonio, Texas.^[200] Five hundred chimpanzees have been retired from laboratory use in the US and live in animal sanctuaries in the US or Canada.^[197] A five-year moratorium was imposed by the US National Institutes of Health in 1996, because too many chimpanzees had been bred for HIV research, and it has been extended annually since 2001.^[200] With the publication of the chimpanzee genome, plans to increase the use of chimpanzees in America were reportedly increasing in 2006, some scientists arguing that the federal moratorium on breeding chimpanzees for research should be lifted.^[200][201] However, in 2007, the NIH made the moratorium permanent.^[202]

Other researchers argue that chimpanzees either should not be used in research, or should be treated differently, for instance with legal status as persons.^[203] Pascal Gagneux, an evolutionary biologist and primate expert at the University of California, San Diego, argues, given chimpanzees' sense of self, tool use, and genetic similarity to human beings, studies using chimpanzees should follow the ethical guidelines used for human subjects unable to give consent.^[200] A recent study suggests chimpanzees which are retired from labs exhibit a form of post-traumatic stress disorder.^[204] Stuart Zola, director of the Yerkes laboratory, disagrees. He told National Geographic: "I don't think we should make a distinction between our obligation to treat humanely any species, whether it's a rat or a monkey or a chimpanzee. No matter how much we may wish it, chimps are not human."^[200]

Only one European laboratory, the Biomedical Primate Research Centre in Rijswijk, the Netherlands, used chimpanzees in research. It formerly held 108 chimpanzees among 1,300 non-human primates. The Dutch ministry of science decided to phase out research at the centre from 2001.^[205] Trials already under way were however allowed to run their course.^[206] Chimpanzees including the female Ai have been studied at the Primate Research Institute of Kyoto University, Japan, formerly directed by Tetsuro Matsuzawa, since 1978. As of 2021, 12 chimpanzees were held at the facility.^[207] Two chimpanzees have been sent into outer space as NASA research subjects. Ham, the first great ape in space, was launched in the Mercury-Redstone 2 capsule on 31 January 1961, and survived the suborbital flight. Enos, the third primate to orbit Earth after Soviet cosmonauts Yuri Gagarin and Gherman Titov, flew on Mercury-Atlas 5 on 29 November of the same year.^[208][209]

Field study

Jane Goodall undertook the first long-term field study of the chimpanzee, begun in Tanzania at Gombe Stream National Park in 1960.^[210] Other long-term studies begun in the 1960s include Adriaan Kortlandt's in the eastern Democratic Republic of the Congo and Toshisada Nishida's in Mahale Mountains National Park in Tanzania.^[211][212] Current understanding of the species' typical behaviour and social organisation has been formed largely from Goodall's ongoing 60-year Gombe research study.^{[115][213][214]}

Goodall researched common chimpanzee social and family life beginning with the Kasakela chimpanzee community in Gombe Stream National Park, Tanzania, in 1960, and documented much original commentary about their experienced emotional life.^[215][216] She found that "it isn't only human beings who have personality, who are capable of rational thought [and] emotions like joy and sorrow". She also observed behaviour often considered human, such as hugs, kisses, pats on the back, and even tickling. Goodall insisted that these gestures are evidence of "the close, supportive, affectionate bonds that develop between family members and other individuals within a community, which can persist throughout a life span of more than 50 years".^[216]

Human immunodeficiency virus

Two primary classes of human immunodeficiency virus (HIV) infect humans: HIV-1 and HIV-2. HIV-1 is the more virulent and easily transmitted, and is the source of the majority of HIV infections throughout the world; HIV-2 occurs mostly in west Africa.^[217] Both types originated in west and central Africa, jumping from other primates to humans. HIV-1 has evolved from a simian immunodeficiency virus (SIVcpz) found in the subspecies P. t. troglodytes of southern Cameroon.^[218][219] Kinshasa, in the Democratic Republic of Congo, has the greatest genetic diversity of HIV-1 so far discovered, suggesting the virus has been there longer than anywhere else. HIV-2 crossed species from a different strain of HIV, found in the sooty mangabey monkeys in Guinea-Bissau.^[217]

The oral polio vaccine AIDS hypothesis (OPV AIDS) is a largely discredited hypothesis which argued the AIDS pandemic originated from live polio vaccines prepared in Common chimpanzee tissue cultures, accidentally contaminated with simian immunodeficiency virus and then administered to up to one million Africans between 1957 and 1960 in experimental mass vaccination campaigns. Originally, a few scientists, notably the evolutionary biologist W. D. Hamilton, thought the hypothesis required serious investigation, but they received little support from the scientific community.^[220] In 2003, Hooper published additional statements that he believed supported his hypothesis in an article in the London Review of Books. In his subsequent book, Hooper also stated that Gaston Ninane was involved in using chimpanzee cells to produce vaccine in Congo. Ninane responded to this allegation by stating that he could "categorically deny" ever having tried to make tissue cultures from chimpanzee cells.^[221] The people involved in vaccine production and distribution from America state that no vaccine was prepared locally in Congo and that only the CHAT vaccine from America was used. Barbara Cohen, the technician who was responsible for running the American laboratory that produced this vaccine stated: "At no time did I ever receive or work on chimpanzee kidneys, nor to my knowledge cells derived from chimpanzees. I never made, nor do I know of anyone in the lab who made polio vaccine in chimpanzee cells."^[222] In 2004, the Origin of Aids, a French TV documentary strongly supportive of the OPV hypothesis, appeared on several television stations around the world.^[223][224]