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Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo Rivermarker forms the boundary between the native habitat of the two species:

Chimpanzees are members of the Hominidae family, along with gorillas, humans, and orangutans. Chimpanzees split from human evolution about 6 million years ago and thus the two chimpanzee species are the closest living relatives to humans, all being members of the Hominini tribe (along with extinct species of Hominina subtribe). Chimpanzees are the only known members of the Panina subtribe. The two Pan species split only about one million years ago.

Evolutionary history

Evolutionary relationship

The taxonomic relationships of Hominoidea
The genus Pan is now considered to be part of the subfamily Homininae to which humans also belong. These two species are the closest living evolutionary relatives to humans, sharing a common ancestor with humans six million years ago. Research by Mary-Claire King in 1973 found 99% identical DNA between human beings and chimpanzees, although research since has modified that finding to about 94% commonality, with at least some of the difference occurring in non-coding DNA. It has been proposed that troglodytes and paniscus belong with sapiens in the genus Homo, rather than in Pan. One of the arguments for this is that other species have been reclassified to belong to the same genus on the basis of less genetic similarity than that between humans and chimpanzees.

Fossils

Many human fossils have been found, but chimpanzee 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. However, chimpanzee fossils have now been reported from Kenyamarker. This would indicate that both humans and members of the Pan clade were present in the East African Rift Valley during the Middle Pleistocene.

Anatomy and physiology

The male common chimp is up to 1.7 m (up to 5.6 ft) high when standing, and weighs as much as 70 kg (154 lb); the female is somewhat smaller. The common chimp’s long arms, when extended, have a span half again as long as the body’s height and are longer than its legs. The bonobo is a little shorter and thinner than the common chimpanzee but has longer limbs. Both species use their long, powerful arms for climbing in trees. On the ground, chimpanzees usually walk on all fours using their knuckles for support with their hands clenched, a form of locomotion called knuckle-walking. Chimpanzee feet are better suited for walking than are those of the orangutan because the chimp’s soles are broader and the toes shorter. Both the common chimpanzee and bonobo can walk upright on two legs when carrying objects with their hands and arms. The coat is dark; the face, fingers, palms of the hands, and soles of the feet are hairless; and the chimp has no tail. A bony shelf over the eyes gives the forehead a receding appearance, and the nose is flat. Although the jaws protrude, the lips are thrust out only when a chimp pouts. The brain of a chimpanzee is about half the size of the human brain.

Chimpanzee testicles are unusually large for their body size, with a combined weight of about compared to a gorilla's or a human's . This is generally attributed to sperm competition due to the polyandrous nature of chimpanzee mating behavior.



The exposed skin of the face, hands and feet varies from pink to very dark in both species, but is generally lighter in younger individuals, darkening as maturity is reached. The Bonobo has proportionately longer upper limbs and tends to walk upright more often than the Common Chimpanzee. A University of Chicago Medical Centre study has found significant genetic differences between chimpanzee populations.

Chimpanzees rarely live past the age of 40 in the wild, but have been known to reach the age of more than 60 in captivity.

Behaviors

Bonobo
Anatomical differences between the Common Chimpanzee and the Bonobo are slight, but in sexual and social behaviour there are marked differences. The Common Chimpanzee has an omnivorous diet, a troop hunting culture based on beta males led by an alpha male, and highly complex social relationships.

The Bonobo, on the other hand, has a mostly frugivorous diet and an egalitarian, nonviolent, matriarchal, sexually receptive behaviour. Bonobos are well known to have frequent sex, with bisexuality the norm for both males and females, and also to use sex to help prevent and resolve conflicts. Different groups of chimpanzees also have different cultural behaviour with preferences for types of tools.

The Common Chimpanzee tends to display higher levels of aggression than the Bonobo.

Intelligence

Diagram of brain.
Topography of the Main Groups of Foci in the Motor Field of Chimpanzee.
Chimpanzees make tools and use them to acquire foods and for social displays; they have sophisticated hunting strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can learn to use symbols and understand aspects of human language including some relational syntax, concepts of number and numerical sequence; and they are capable of spontaneous planning for a future state or event.

Tool use

One of the most significant discoveries was in October 1960 when Jane Goodall observed the use of tools among chimpanzees. Recent research indicates that chimpanzee stone tool use dates to at least 4,300 years ago. A recent study revealed the use of such advanced tools as spears, which Common Chimpanzees in Senegalmarker sharpen with their teeth, being used to spear Senegal Bushbabies out of small holes in trees. Before the discovery of tool use in chimps, it was believed that humans were the only species to make and use tools, but several other tool-using species are now known.

Empathy

Chimpanzee mother and baby
Recent studies have shown that chimpanzees engage in apparently altruistic behaviour within groups, but are indifferent to the welfare of unrelated group members.

Evidence for "chimpanzee spirituality" includes display of mourning, "incipient romantic love", "rain dance", appreciation of natural beauty such as a sunset over a lake, curiosity and respect towards wildlife (such as the python, which is neither a threat nor a food source to chimpanzees), empathy toward other species (such as feeding turtles) and even "animism" or "pretend play" in chimps cradling and grooming rocks or sticks.

Communication

Chimps communicate in a manner similar to human non-verbal communication, using vocalizations, hand gestures, and facial expressions. Research into the chimpanzee brain has revealed that chimp communication activates an area of the chimp brain that is in the same position as Broca's area, the language center in the human brain.

Studies of language

Side profile of a Chimpanzee
Scientists have long been fascinated with the studies of language, believing it to be a unique human cognitive ability. To test this hypothesis, scientists have attempted to teach human language to several species of great apes. One early attempt by Allen and Beatrice 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 that he had spontaneously taught them to other chimpanzees. Over a longer period of time, Washoe learned over 800 signs.

There is ongoing debate among some scientists, notably Noam Chomsky and David Premack, about non-human great apes' ability to learn language. Since the early reports on Washoe, numerous other studies have been conducted with varying levels of success, including one involving a chimpanzee named, in parody, Nim Chimpsky, trained by Herbert Terrace of Columbia University. Although his initial reports were quite positive, in November 1979, Terrace and his team 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 re-analysis, Terrace 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’ behavior is pure drill,” he said. “Language still stands as an important definition of the human species.” In this reversal, Terrace now argued that Nim’s use of ASL was not like human language acquisition. Nim never initiated conversations himself, rarely introduced new words, and simply imitated what the humans did. Nim’s sentences also did not grow in length, unlike human children whose vocabulary and sentence length show a strong positive correlation.

Memory

A 30-year study at Kyoto Universitymarker’s Primate Research Institutemarker has shown that chimps are able to learn to recognize the numbers 1-9 and their values. The chimps further show an aptitude for photographic memory, demonstrated in experiments in which the jumbled digits 1-9 are flashed onto a computer screen for less than a quarter of a second, after which the chimp, Ayumu, is able to correctly and quickly point to the positions where they appeared in ascending order. The same experiment was failed by world memory champion Ben Pridmore on most attempts.

Laughter in apes

Young chimpanzees playing
Laughter might not be confined or unique to humans. The differences between chimpanzee and human laughter may be the result of adaptations that have evolved to enable human speech. Self-awareness of one's situation as seen in the mirror test, or the ability to identify with another's predicament (see mirror neurons), are prerequisites for laughter, so animals may be laughing in the same way that humans do.

Chimpanzees, gorillas, and orangutans show laughterlike vocalizations in response to physical contact, such as wrestling, play chasing, or tickling. This is documented in wild and captive chimpanzees. Common Chimpanzee laughter is not readily recognizable to humans as such, because it is generated by alternating inhalations and exhalations that sound more like breathing and panting. There are instances in which non-human primates have been reported to have expressed joy. One study analysed and recorded sounds made by human babies and Bonobos when tickled. It found that although the Bonobo's laugh was a higher frequency, the laugh followed a pattern similar to that of human babies and included similar facial expressions. Humans and chimpanzees share similar ticklish areas of the body, such as the armpits and belly. The enjoyment of tickling in chimpanzees does not diminish with age.
See also: Laughter in animals


Aggression

Male chimpanzees in Mahale National Park, Tanzania


Adult Common Chimpanzees, particularly males, can be very aggressive. They are highly territorial and are known to kill other chimps. Chimpanzees also engage in targeted hunting of lower order primates such as the red colobus and bush babies, and use the meat from these kills as a "social tool" within their community. In February 2009, after a relatively rare incident in which a pet chimp named Travis attacked a woman in Stamford, Connecticutmarker, the U.S. House of Representatives approved a primate pet ban in the United States.

Interactions with humans

History

Africans have had contact with chimpanzees for millennia. Chimpanzees have been kept as pets for centuries in a few African villages, especially in Congomarker. The first recorded contact of Europeans with chimps took place in present-day Angolamarker during the 1600s. The diary of Portuguesemarker explorer Duarte Pacheco Pereira (1506), preserved in the Portuguese National Archive (Torre do Tombo), is probably the first European document to acknowledge that chimpanzees built their own rudimentary tools.

The first use of the name "chimpanzee", however, did not occur until 1738. The name is derived from a Tshiluba language term "kivili-chimpenze", which is the local name for the animal and translates loosely as "mockman" or possibly just "ape". The colloquialism "chimp" was most likely coined some time in the late 1870s. Biologists applied Pan as the genus name of the animal. Chimps as well as other apes had also been purported to have been known to Western writers in ancient times, but mainly as myths and legends on the edge of European and Arab societal consciousness, mainly through fragmented and sketchy accounts of European adventurers. Apes are mentioned variously by Aristotle, as well as the Bible, where apes and baboons are described as having been collected by Solomon in 1 Kings 10:22.

The first of these early transcontinental chimpanzees came from Angola and were presented as a gift to Frederick Henry, Prince of Orange in 1640, and were followed by a few of its brethren over the next several years. Scientists described these first chimpanzees as "pygmies", and noted the animals' distinct similarities to humans. The next two decades would see a number of the creatures imported into Europe, mainly acquired by various zoological gardens as entertainment for visitors.



Darwin's theory of natural selection (published in 1859) spurred scientific interest in chimpanzees, as in much of life science, leading eventually to numerous studies of the animals in the wild and captivity. The observers of chimpanzees at the time were mainly interested in behaviour as it related to that of humans. This was less strictly and disinterestedly scientific than it might sound, with much attention being focused on whether or not the animals had traits that could be considered 'good'; the intelligence of chimpanzees was often significantly exaggerated, as immortalized in Hugo Rheinhold's Affe mit Schädel (see image, left). By the end of the 1800s chimpanzees remained very much a mystery to humans, with very little factual scientific information available.

The 20th century saw a new age of scientific research into chimpanzee behaviour. Before 1960, almost nothing was known about chimpanzee behaviour in their natural habitat. In July of that year, Jane Goodall set out to Tanzania's Gombemarker forest to live among the chimpanzees, where she primarily studied the members of the Kasakela chimpanzee community. Her discovery that chimpanzees made and used tools was groundbreaking, as humans were previously believed to be the only species to do so. The most progressive early studies on chimpanzees were spearheaded primarily by Wolfgang Köhler and Robert Yerkes, both of whom were renowned psychologists. Both men and their colleagues established laboratory studies of chimpanzees focused specifically on learning about the intellectual abilities of chimpanzees, particularly problem-solving. This typically involved basic, practical tests on laboratory chimpanzees, which required a fairly high intellectual capacity (such as how to solve the problem of acquiring an out-of-reach banana). Notably, Yerkes also made extensive observations of chimpanzees in the wild which added tremendously to the scientific understanding of chimpanzees and their behaviour. Yerkes studied chimpanzees until World War II, while Köhler concluded five years of study and published his famous Mentality of Apes in 1925 (which is coincidentally when Yerkes began his analyses), eventually concluding that "chimpanzees manifest intelligent behaviour of the general kind familiar in human beings ... a type of behaviour which counts as specifically human" (1925).

The August, 2008, issue of the American Journal of Primatology reports results of a year-long study of chimpanzees in Tanzania’s Mahale Mountains National Park which produced evidence that chimpanzees are becoming sick from viral infectious diseases they have likely contracted from humans. Molecular, microscopic and epidemiological investigations demonstrated that the chimpanzees living at Mahale Mountains National Park have been suffering from a respiratory disease that is likely caused by a variant of a human paramyxovirus.

Studies

As of November 2007, there were 1,300 chimpanzees housed in 10 U.S. laboratories (out of 3,000 great apes living in captivity there), either wild-caught, or acquired from circuses, animal trainers, or zoos. Most of the labs either conduct or make the chimps available for invasive research, 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". Two federally funded laboratories use chimps: Yerkes National Primate Research Laboratory at Emory Universitymarker in Atlanta, Georgia, and the Southwest National Primate Center in San Antonio, Texas. Five hundred chimps have been retired from laboratory use in the U.S. and live in sanctuaries in the U.S. or Canada.

Chimpanzees used in biomedical research tend to be used repeatedly over decades, rather than used and killed as with most laboratory animals. Some individual chimps currently in U.S. laboratories have been used in experiments for over 40 years. According to Project R&R, a campaign to release chimps held in U.S. labs — run by the New England Anti-Vivisection Society in conjunction with Jane Goodall and other primate researchers — the oldest known chimp in a U.S. lab is Wenka, who was born in a laboratory in Florida on May 21, 1954. She was removed from her mother on the day of birth to be used in a vision experiment that lasted 17 months, then sold as a pet to a family in North Carolina. She was returned to the Yerkes National Primate Research Center in 1957 when she became too big to handle. Since then, she has given birth six times, and has been used in research into alcohol use, oral contraceptives, ageing, and cognitive studies. Wenka, Project R&R, New England Anti-Vivisection Society.

With the publication of the chimpanzee genome, there are reportedly plans to increase the use of chimps in labs, with some scientists arguing that the federal moratorium on breeding chimps for research should be lifted. A five-year moratorium was imposed by the U.S. National Institutes of Health (NIH) in 1996, because too many chimps had been bred for HIV research, and it has been extended annually since 2001.

Other researchers argue that chimps are unique animals and either should not be used in research, or should be treated differently. Pascal Gagneux, an evolutionary biologist and primate expert at the University of California, San Diegomarker, argues that, given chimpanzees' sense of self, tool use, and genetic similarity to human beings, studies using chimps should follow the ethical guidelines that are used for human subjects unable to give consent. Also, a recent study suggests that chimpanzees which are retired from labs exhibit a form of posttraumatic stress disorder. Stuart Zola, director of the Yerkes National Primate Research 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."

An increasing number of governments are enacting a Great Ape research ban forbidding the use of chimpanzees and other great apes in research or toxicology testing. As of 2006, Austriamarker, New Zealandmarker, the Netherlandsmarker, Swedenmarker, and the UKmarker had introduced such bans.

Attacks on humans

Common Chimpanzees have been known to attack humans on occasion. There have been many attacks in Uganda by chimpanzees against human children; the results are sometimes fatal for the children. Some of these attacks are presumed to be due to chimpanzees being intoxicated (from alcohol obtained from rural brewing operations) and mistaking human children for the Western Red Colobus, one of their favourite meals. The dangers of careless human interactions with chimpanzees are only aggravated by the fact that many chimpanzees perceive humans as potential rivals. With up to five times the upper body strength of a human, an angered chimpanzee could easily overpower and potentially kill a fully grown man, as shown by the attack and near death of former NASCAR driver St. James Davis. Another example of chimpanzee to human aggression occurred February 2009 in Stamford, Connecticut, when a 200 pound, 14 year old pet chimp named Travis attacked his owner's friend, who lost her hands, eyelids, nose and part of her upper jaw/sinus area from the attack. There are at least 6 documented cases of chimpanzees snatching and eating human babies.

In popular culture

Chimpanzees have been commonly stereotyped in popular culture, where they are most often cast in standardized roles 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. Accordingly, entertainment acts featuring chimpanzees dressed up as humans have been traditional staples of circuses and stage shows.

In the age of television, a new genre of chimp act emerged in the United Statesmarker: series whose cast consisted entirely of chimpanzees dressed as humans and "speaking" lines dubbed by human actors. These shows, examples of which include Lancelot Link, Secret Chimp in the 1970s or The Chimp Channel in the 1990s, relied on the novelty of their ape cast to make their timeworn, low comedy gags funny. Their chimpanzee "actors" were as interchangeable as the apes in a circus act, being amusing as chimpanzees and not as individuals.

When chimpanzees appear in other TV shows, they generally do so as comic relief sidekicks to humans. In that role, for instance, J. Fred Muggs appeared with Today Show host Dave Garroway in the 1950s, "Judy" on Daktari in the 1960s or "Darwin" on The Wild Thornberrys in the 1990s. Chimpanzee characters and actions are almost never relevant to the plot, in contrast to the fictional depictions of other animals, such as dogs (as in Lassie), dolphins (Flipper), horses (The Black Stallion) or even other great apes (King Kong).

The rare exceptions – depictions of chimpanzees as individuals rather than stock characters, and as central rather than incidental to the plot – are usually found in science fiction. Robert A. Heinlein's short story Jerry Was a Man of 1947 centers on a genetically enhanced chimpanzee suing for better treatment, a theme also echoed in David Brin's 1990s Uplift series. In film, the 1972 movie Conquest of the Planet of the Apes centers on a fierce revolt of enslaved apes, led by the chimpanzee Caesar, against their human masters. In one episode of Monk, a chimp was in danger of being euthanized after it was thought to have killed its owner.

See also



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