Chimpanzees spend much time on the ground, where they walk on all fours, using the soles of the feet and the knuckles of the hands; they can also stand on two legs and sometimes walk this way for short distances. They climb trees in pursuit of food and for nesting and can swing by their hands from branch to branch. Their diet consists largely of fruit and other plant matter, but they also hunt and eat small animals, including monkeys. They use and even make primitive tools; for example, they collect termites using twigs and crack nuts using stones. Many primatologists now attribute culture to chimpanzees, noting learned variations in such skills and habits among different groups.
Chimpanzees move about the forest in bands of varying composition, usually numbering six to ten individuals. The males of a group engage in dominance contests involving much screaming and stamping. Family groups consist of mothers and offspring; females mate with many males during their fertile periods. A single infant is born every three to eight years; young chimpanzees ride about on their mothers' backs. Under ideal circumstances chimpanzees may live 50 years.
Although incapable of speech beyond their own simple vocalizations, captive chimpanzees have been taught to communicate in a language using visual rather than verbal symbols. Because of their close evolutionary relationship to humans they are often used for medical and behavioral experimentation, but the degree to which chimpanzees and humans are genetically close is a subject of dispute, with estimates of the amount of DNA the species share ranging from 94.6% to 99.4%. Chimpanzees, especially bonobos, are considered endangered species because of hunting and loss of habitat.
Chimpanzees are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Primates, family Pongidae.
See G. H. Bourne, The Chimpanzee (6 vol., 1973); J. Goodall, In the Shadow of Man (1967) and The Chimpanzees of Gombe (1986); F. de Waal, Bonobo: The Forgotten Ape (1998).
Chimpanzees are members of the Hominidae family, along with gorillas, humans, and orangutans. 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.
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. 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. 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.
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 Euro-Arabic 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.
When chimpanzees first began arriving on the European continent, European scientists noted the inaccuracy of some ancient descriptions, which often reported that chimpanzees had horns and hooves. 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 who examined these rare specimens were baffled, and 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 evolution (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. At one point there was even a scheme drawn up to domesticate chimpanzees in order to have them perform various menial tasks (i.e. factory work). 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 Gombe forest to live among the chimpanzees. 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).
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, and by the fact that the average chimpanzee has over 5 times the upper-body strength of a human male. As a result virtually any angered chimpanzee can easily overpower and potentially kill even a fully grown man, as shown by the attack and near death of former NASCAR driver Saint James Davis.
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.
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.
Scientists have long been fascinated with the studies of language, as it was potentially the most uniquely human cognitive ability. To test the hypothesis of the human uniqueness of language, scientists have attempted to teach several species of great apes language. One early attempt was performed by Allen and Beatrice Gardner in the 1960s, in which they spent 51 months attempting to teach a chimpanzee, named Washoe, American Sign Language. Washoe reportedly learned 151 signs in those 51 months. Over a longer period of time, Washoe reportedly learned over 800 signs. Numerous other studies including one involving a chimpanzee named Nim Chimpsky have been conducted since with varying levels of success. There is ongoing debate among some scientists, notably Noam Chomsky and David Premack, about the great apes' ability to learn language.
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.
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 University 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.
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 Diego, 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. 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, Austria, New Zealand, the Netherlands, Sweden, and the UK had introduced such bans.
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. Humans shared a common ancestor with chimpanzees five to eight million years ago. Groundbreaking 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 'junk' DNA. It has even been proposed that troglodytes and paniscus belong with sapiens in the genus Homo, rather than in Pan. One argument 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.
A study published by Clark and Nielsen of Cornell University in the December 2003 issue of the journal Science highlights differences related to one of humankind's defining qualities — the ability to understand language and to communicate through speech. These macro-phenotypic differences, however, may owe less to physiology than might be assumed given that Homo sapiens developed modern cultural features long after the modern physiological features were in place and indeed competed averagely against other species of Homo with regard to tools, etc. for many millennia. Differences also exist in the genes for smell, in genes that regulate the metabolism of amino acids and in genes that may affect the ability to digest various proteins. See the history of hominoid taxonomy for more about the history of the classification of chimpanzees. See Human evolutionary genetics for more information on the speciation of humans and great apes.