Chimpanzee

© Image: Curt Busse
A Chimpanzee at Gombe - Photo by Curt Busse.

The Chimpanzee (pan troglodytes), also known as the Common Chimpanzee, is part of the Hominidae family, which also includes the Bonobo, the Orangutan, the Gibbon, the Gorilla, and the Human. Chimpanzees can be found in West and Central Africa. They live to the north of the Congo River in the Democratic Republic of Congo. The Bonobo Chimpanzee (pan paniscus) lives south of the Congo River.

Measurements

A full-grown adult male weighs an average of 132.3lbs (60kg) and is 3-4 ft tall (.9-1.2 meters). A full grown adult female weighs an average of 104.5lbs (47.4kg) and are 2 – 31/2 feet tall (.66-1m). The sexual dimorphism in Chimpanzees is similar to that in Humans. Their brain size is 300cc on average and their brain resembles a human brain structurally.

Diet

Chimpanzees are primarily vegetarian. The bulk of their diet consists of fruit, leaves, flowers, and seeds. Chimpanzees form hunting parties and go out in search of colobus monkeys. When hunting each chimpanzee has a different role within the hunting party. The fasted and strongest chimpanzee in the group chases the prey while the others block off the exits. The members of the hunting party can’t see each other during this process which shows their incredible cognitive mapping ability. A cultural difference between the Gombe and Tai Forest Chimpanzees can be seen in how they eat the Colobus monkeys. Gombe Chimpanzees eat them when they are dead whereas Tai Forest Chimpanzees eat them while they are still alive.

Dentition

Chimpanzee's Mandibular M1s erupt at age 3.3 years. Their dentition is completed at 11.5 years of age.

Lifespan

Their maximum known life span is 53 years.

Habitat

Chimpanzees live in Western and Central Africa, in savannah woodlands, grasslands, lowland rain forests, and mountain rain forests.

Locomotion

The Common Chimpanzee is both arboreal and terrestrial. Chimpanzees are quadrupeds, they walk on all four limbs whereas humans are bi-pedal and walk on only two limbs. Since they are quadrupeds they knuckle-walk while on the ground. Chimpanzees brachiate while living in the trees. They are also cable of suspensory motion, arboreal climbing, and can walk bi-pedaly for a distance while holding tools or food.

Social Structure

Chimpanzees have an average party size of 10 members. An Alpha male leads the troop and the male chimpanzees are constantly playing politics either with brute force or diplomatic grooming. Females leave their natal groups when they sexually mature. Males have dominance over females although there is a dominance hierarchy within the females as well. Their society is fission-fusion and patrilneal multi-male, multi-female.

Social Mechanisms

Displays

Chimpanzees use a number of social mechanisms to communicate with each other and increase their social rankings. Chimpanzees have two different types of displays they use a ventilating, which consists of inhaling rhythmically and loud hooting, is used as a challenging display and communicates to the rest of the group the intentions of the displayer. When Chimpanzees want to that the are self-confident and assertive they an inflated display in which they press their lips together and hold their breath while they puff out their chest and their lips eventually bulge under the pressure.

Triadic Awareness

Because Chimpanzee hierarchies are based on coalitions Chimpanzees need triadic awareness, the ability to recognize the social relationship between others. Their triadic awareness is of special significance for male Chimpanzees because they need to know who to align themselves with in order to bring themselves closer to the role of Alpha male.

The Female Hierarchy

Physical strength is much less of a factor in a female Chimpanzee hierarchy than in a male hierarchy. The important traits needed to become alpha female in a Chimpanzee troop are personality and age. Conflict between females is rare. The female hierarchy studied by Franz De Waal in the 1980s was based completely on respect from inferior ranking members. Acceptance of dominance is more important to females than displaying dominance. Although the females in a Chimpanzee troop are not as powerful as the males they are able to remove objects such as food from the hands of males without resistance. De Waal suggests the females posses leverage over the males in the form of sexual and political favors. The Alpha Female often brings peace to a conflict by simply being present.

Reciprocity

The theory of reciprocity is prevalent in Chimpanzee society. Evidence for it is seen in their strategic coalitions, nonintervention alliances, sexual bargaining, and even reconciliation blackmail (when a Chimpanzee will refuse to greet another Chimpanzee until he greets a third Chimpanzee). Alpha males (If aggressive) will punish others for not supporting them against their rivals by beating them whereas if their rivals support them they opt not to beat them. De Wall exclaims the two basic rules of chimpanzee group life are, "one good turn deserves another" and "an eye for an eye, a tooth for a tooth" although as with all rules they aren't obeyed 100 percent of the time.

Reconciliation

After two males have fought there is often reconciliation. During the reconciliation processes both males are unarmed and there is a large amount of eye contact. During conflict male chimpanzees avoid eye contact. Opponents sit across from each other for what could be hours at a time until they manage to make eye contact. After eye contact is made they look into each others eyes until the reconciliation is complete. Chimpanzees have also been seen to make truces for the night when they return to their sleeping quarters in captivity.

Alpha Male

The role of the alpha male in chimpanzee society is a control role. Granted different alpha males will act differently depending on their personalities. For example Frodo, the former alpha male of the Gombe chimpanzees studied by Goodall ruled his troop using violence and when he was finally dethroned he was forcefully removed from the troop by the other males. Whereas when Luit was the alpha male of the troop at Arnheim, studied by De Waal, he did his best to keep the peace and provide security for his troop members. He would prevent conflicts by supporting the losers. Although when Luit was not alpha male he would bat the females in the alpha males presence to show how they could not count on the current alpha male for security. This suggests that the control role of alpha male is the duty of the alpha male and not a privilege. The general role of the alpha male is to provide peace and security to the troop in exchange for sexual privileges and other power.

Violence

Chimpanzees compete violently within their own social group in order to gain rank in the social hierarchy or display dominance to maintain ones rank in the hierarchy. Violence also occurs between rival Chimapanzee troops. Male chimpanzees often patrol their territory and numerous occasions have been documented of Chimpanzees organizing hunting parties and militaristically venturing into another troops territory to ambush and kill a rival chimpanzee. The two categories of violence are in-group violence in which the violence is contained to a certain level and is used primarily as a social tool. Out-group violence is lethal and done sporadically. These Male assassination squads sometimes even kidnap (chimpnap) a female chimpanzee after beating her into submission.

Culture & Tool Use

Gombe Chimpanzees

The Gombe chimpanzees display a socially learned pattern of behavior (culture) by termite probing. These chimpanzees termite probe by first finding a stick of proper length and using it as a tool to penetrate the termite nests and fish out the termites inside. This complex behavior is learned from their mothers.

Tai Forest Chimpanzees

In the Tai forest the Chimpanzees eat Panda nuts which requires the use of stones as anvil and hammer in order to open. The proper rocks needed to open the nuts are found far from the location of the Panda Nuts so the ability to form a cognitive map is necessary for the task. The young chimpanzee are actively taught how to open panda nuts by the adults.

Communication

Chimpanzees have been taught to perform American Sign Language. Washoe is one of the first chimpanzees able to communicate with ASL. The realization that chimpanzees have the ability to comprehend ASL sheds light upon the powerful cognitive abilities of Chimpanzees. Washoe was able to teach some of her learned sign language to her adopted son Loulis. Chimpanzees have the cognitive ability to process language as well as a 5 year old human child. Chimpanzees express their moods to each other by their facial expressions, specifically how much of their teeth they choose to bare. The most popular hand gesture in a chimpanzee society is an extended arm with an open palm. Its significance depends largely on the context it is used. Some of its uses are to beg, initiate physical contact, or ask for support either physically or politically.

Evolution of the Species

Bonobo Chimpanzees and the Founder Effect Theory

It is argued that the Bonobo chimpanzee evolved from the Common chimpanzee via the Founder Effect. The Founder Effect is when a small group of a population becomes isolated from the original and they may evolve differently due to both their environment if enough time is presented for natural selection and the limited genetic variation in relation to the original population. The evidence for this argument is that Common chimpanzees are blood types A and O whereas Bonobo chimpanzees are only blood type A. Also the fact that the Common and Bonobo chimpanzees are separated by the Congo River and their competition for food is different. South of the Congo River there aren’t any gorillas for Bonobos to compete with for resources which explains the difference in social structure among the two species.

Genetics

DNA

Chimpanzee DNA differs from Gorillas 2.37% and from Humans 1.63%. Chimpanzees are the closest known relative to homo sapiens.