The common chimpanzee (Pan troglodytes), also known as the robust chimpanzee, is a great ape. The name troglodytes, Greek for 'cave-dweller', was coined by Johann Friedrich Blumenbach in his Handbuch der Naturgeschichte (Handbook of Natural History) published in 1779. Colloquially, the common chimpanzee is often called the chimpanzee (or simply 'chimp'), though technically this term refers to both species in the genus Pan: the common chimpanzee and the closely-related bonobo, formerly called the pygmy chimpanzee. Evidence from fossils and DNA sequencing show that both species of chimpanzees are the sister group to the modern human lineage. The common chimpanzee is an endangered species.
Jane Goodall undertook the first long-term field study of the common chimpanzee, begun in Tanzania at Gombe Stream National Park in 1960. Other long-term study sites begun in 1960 include A. Kortlandt in eastern Democratic Republic of the Congo and Junichiro Itani in Mahale Mountains National Park in Tanzania. Current understanding of the species' typical behaviors and social organization are formed largely from Goodall's ongoing 50-year Gombe research study.
DNA evidence published in 2005 suggests the bonobo and common chimpanzee species separated from each other less than one million years ago (similar in relation between Homo sapiens and Neanderthals). The chimpanzee line split from the last common ancestor of the human line approximately six million years ago. Because no species other than Homo sapiens has survived from the human line of that branching, both chimpanzee species are the closest living relatives of humans. The chimpanzee's genus, Pan, diverged from the gorilla's genus about seven million years ago.
Several subspecies of the common chimpanzee have been recognized:
- Central chimpanzee, Pan troglodytes troglodytes, in Cameroon, the Central African Republic, Equatorial Guinea, Gabon, the Republic of the Congo, and the Democratic Republic of the Congo;
- Western chimpanzee, Pan troglodytes verus, in Guinea, Mali, Sierra Leone, Liberia, Côte d'Ivoire, Ghana, and Nigeria;
- Nigeria-Cameroon chimpanzee, Pan troglodytes ellioti, in Nigeria and Cameroon;
- Eastern chimpanzee, Pan troglodytes schweinfurthii, in the Central African Republic, the Sudan, the Democratic Republic of the Congo, Uganda, Rwanda, Burundi, Tanzania, and Zambia.
Human and common chimpanzee DNA are very similar. After the completion of the Human Genome Project, a Chimpanzee Genome Project was initiated. In December 2003, a preliminary analysis of 7600 genes shared between the two genomes confirmed that certain genes, such as the forkhead-box P2 transcription factor which is involved in speech development, have undergone rapid evolution in the human lineage. A draft version of the chimpanzee genome was published on September 1, 2005, in an article produced by the Chimpanzee Sequencing and Analysis Consortium. The DNA sequence differences between humans and chimpanzees is about thirty-five million single-nucleotide changes, five million insertion/deletion events, and various chromosomal rearrangements. Typical human and chimp protein homologs differ in only an average of two amino acids. About 30% of all human proteins are identical in sequence to the corresponding chimp protein. Duplications of small parts of chromosomes have been the major source of differences between human and chimp genetic material; about 2.7% of the corresponding modern genomes represent differences, produced by gene duplications or deletions, during the approximately four to six million years since humans and chimps diverged from their common evolutionary ancestor. Results from human and chimp genome analyses, currently being conducted by geneticists including David Reich, should help in understanding the genetic basis of some human diseases.
Adults in the wild weigh between 40 and 65 kg (88 and 140 lb), though males in captivity such as Travis the Chimp have reached 200 pounds; males can measure up to 1.6 m (5 ft 3 in) and females to 1.3 m (4 ft 3 in). Their body is covered by a coarse black hair, except for the face, fingers, toes, palms of the hands and soles of the feet. Both their thumbs and their big toes are opposable, allowing a precision grip. Their gestation period is eight months. Infants are weaned when they are about three years old, but usually maintain a close relationship with their mother for several more years; they reach puberty at the age of eight to ten, and their lifespan in captivity is about fifty years.
Common chimpanzees are found in the tropical forests and wet savannas of Western and Central Africa. They once inhabited most of this region, but their habitat has been dramatically reduced in recent years.
The chimpanzee diet is primarily vegetarian, although the chimpanzee is omnivorous and also eats meat. The primary chimpanzee diet consists of fruits, leaves, nuts, seeds, tubers, and other miscellaneous vegetation. Termites are also eaten regularly in some populations. Western Red Colobus Monkeys (Piliocolobus badius) are sometimes hunted by the chimpanzee, although Jane Goodall documented many occasions within Gombe Stream National Park of chimpanzees and Western Red Colobus Monkeys ignoring each other within close proximity. Chimpanzees will typically spend six to eight hours a day eating.
In some cases, chimpanzees have been documented killing leopard cubs, though this primarily seems to be a protective effort, since the leopards are the main natural predators of the chimpanzees. Lions may have also preyed on chimps at the Mahale field study site, where as many as 6% of the chimpanzees studied have fallen prey to lions. Isolated cases of cannibalism have also been documented.
Common chimpanzees live in communities that typically range from 20 to more than 150 members, but spend most of their time travelling in small, temporary groups consisting of a few individuals, "which may consist of any combination of age and sex classes." Both males and females will sometimes travel alone. Common chimpanzees are both arboreal and terrestrial, spending equal time in the trees and on the ground. Their habitual gait is quadrupedal, using the soles of their feet and resting on their knuckles, but they can walk upright for short distances. Common chimpanzees are 'knuckle walkers', like gorillas, in contrast to the quadrupedal locomotion of orangutans and bonobos, 'palm walkers' who use the outside edge of their palms.
The common chimpanzee lives in a fission-fusion society, where mating is promiscuous, and may be found in groups of the following types: all-male, adult females and offspring, consisting of both sexes, or one female and her offspring. Chimpanzees have complex social relationships and spend a large amount of time grooming each other. At the core of social structures are males, who roam around, protect group members, and search for food. Among males, there is generally a dominance hierarchy. 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," is highly variable in terms of which particular individual chimpanzees congregate at a given time. This is mainly due to chimpanzees having a high level of individual autonomy within their fission-fusion social groups. Also, communities have large ranges that overlap with those of other groups.
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 who regularly come into contact and congregate into parties in a particular area.) As stated, these smaller groups also emerge in a variety of types, for a variety of purposes. For example, an all-male troop may be organized in order to hunt for meat, while a group consisting of one mature male and one mature female may occur for the purposes of copulation. An individual may encounter certain individuals quite frequently, but have run-ins with others almost never or only in large-scale gatherings. Due to the varying frequency at which chimpanzees associate, the structure of their societies is highly complicated.
The chimpanzee makes a night nest in a tree in a new location every night, with every chimpanzee in a separate nest other than infants or small chimpanzees, who sleep with their mothers.
Chimpanzees have been described as highly territorial and are known to kill other chimps, although Margaret Power wrote in her 1991 book The Egalitarians that the field studies from which the aggressive data came, Gombe and Mahale, use artificial feeding systems that increased aggression in the chimpanzee populations studied and therefore might not reflect innate characteristics of the species as a whole. In the years following her artificial feeding conditions at Gombe, Jane Goodall described groups of male chimps patrolling the borders of their territory brutally attacking chimps who had split off from the Gombe group. A study published in 2010 found that chimpanzees conduct wars over land, not mates. Patrol parties from smaller groups are more likely to avoid contact with their neighbors. Patrol parties from large groups will even take over a smaller group's territory, gaining access to more resources, food, and females.
When confronted by a predator, chimpanzees will react with loud screams and use any object they can against the threat.
While it has been known since Jane Goodall's 1960s discovery that modern chimpanzees use tools, research published in 2007 indicates that chimpanzee stone tool use dates to at least 4,300 years ago. A common chimpanzee from the Kasakela chimpanzee community was the first non-human animal observed making a tool, by modifying a twig to use as an instrument for extracting termites from their mound. Chimpanzees have also been observed using leaves as napkins and towels.
A recent study revealed the use of such advanced tools as spears, which West African chimpanzees in Senegal sharpen with their teeth, being used to spear Senegal Bushbabies out of small holes in trees. An eastern chimpanzee has been observed using a modified branch as a tool to capture a squirrel.
Interaction with 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 5 times the upper body strength of a human, an angered chimpanzee could easily overpower and potentially kill even a fully grown man, as shown by the attack on 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 (91 kg), 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.
Link with Human Immunodeficiency Virus type 1
Two types 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 is largely confined to west Africa. Both types originated in west and central Africa, jumping from primates to humans. HIV-1 has evolved from a Simian Immunodeficiency Virus (SIVcpz) found in the common chimpanzee subspecies, Pan troglodytes troglodytes, native to southern Cameroon. Kinshasa, in the Democratic Republic of Congo, has the greatest genetic diversity of HIV-1 so far discovered, suggesting that the virus has been there longer than anywhere else. HIV-2 crossed species from a different strain of SIV, found in the Sooty Mangabey, monkeys in Guinea-Bissau.
Status and conservation
Chimpanzees are protected by law in most countries and they are present in numerous national parks throughout their range, although many populations occur outside protected areas.
The biggest threats to the common chimpanzee are habitat destruction, poaching and disease. Deforestation across West and Central Africa has severely reduced chimpanzee habitats. It is estimated that more than 80% of the region’s original forest cover has been lost. Increased accessibility to remote areas through road building poses a risk to chimpanzee populations through habitat degradation and fragmentation and potential increased poaching in areas previously not seriously impacted by such anthropogeniic pressures. In western Central Africa deforestation rates are low but selective logging is, or will be, carried out in the majority of forests outside national parks.
Chimpanzee are a common target for poachers. Chimpanzees currently constitute 1% to 3% of bushmeat sold in urban markets in Côte d’Ivoire. They are also taken in pet trades. Although the pet trade is illegal in all range countries that are signatories to CITES, it persists illegally across Africa. In some localities, chimpanzees are hunted traditionally for medicinal purposes Some range countries, such as Guinea, still officially permit the capture of chimpanzees for scientific research. People will kill chimpanzees intentionally to protect their crops using snares.
Infectious diseases are a main cause of death for chimpanzees. Because chimpanzees and humans are so similar, chimpanzees succumb to many diseases that afflict humans. The frequency of encounters between chimpanzees and humans and/or human waste is increasing as human populations expand, leading to higher risks of disease transmission between humans and chimpanzees.
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- General references
- Johann Friedrich Blumenbach, De Generis Humani Varietate Nativa, 1775.
- Tutin CEG, McGrew WC, Baldwin PJ 1983. Social organization of savanna-dwelling chimpanzees, Pan troglodytes verus, at Mt. Assirik, Senegal. Primates, 24, 154-173.