Chimpanzees, the most socially diverse group of apes, are represented by two species, the common chimpanzee (Pan troglodytes) and the pygmy chimpanzee, or bonobo (Pan paniscus). Both species are found in the tropical forests of equatorial Africa. Sharing approximately 98% of their genes with humans, chimpanzees are genetically more closely related to humans than they are to any other ape group. For this reason, the chimpanzee has been important to the study of human evolution and behavior.
The common chimpanzee is found in many parts of equatorial Africa, inhabiting the forested regions of 22 countries. The variation in flora and fauna between these different areas has enabled the common chimpanzee to evolve into at least three separate subspecies that are localized to specific regions. The three subspecies are Pan troglodytes troglodytes from central Africa; Pan troglodytes verus from western Africa; and Pan troglodytes schweinfurthii from eastern Africa. Two other subspecies, P. troglodytes vellerosus from Nigeria and P. troglodytes koolokamba from Cameroon and Gabon, have been proposed, yet these designations are considered more controversial.
The common chimpanzee lives in multimale-multifemale polygynous groups with a single dominant male, several mature males, and several mature females and their offspring. Males tend to remain in their natal groups while females emigrate. This sets up a social dynamic in which males often form alliances with other males, usually related individuals, and females only form loose bonds with each other. Like other polygynous primates, chimpanzees display significant sexual dimorphism, with males weighing on average 60 kg (132 lb) and females weighing 47 kg (104 lb). The social interactions between members of this species include vocal, physical, and gesturalvisual behaviors, some of which are typical of most primates and others that are specific either to the species or local population.
The second species of chimpanzee is the bonobo or “pygmy chimpanzee” from the central Congo Basin. Male bonobos weigh on average 45.0 kg (99.2 lb), while females weigh 33.2 kg (73.2 lb). This species, which is the more gracile cousin of the common chimpanzee, not a smaller version, has been little studied compared with the more popular common chimpanzees studied by Jane Goodall and others. However, the little that is known about this species indicates that it is very different from any other ape species in terms of behavior.
Bonobos live in multimale-multifemale groups where the group hierarchy appears to be divided between a dominant male and a dominant female. As opposed to the more aggressive interactions seen in the common chimpanzees, bonobo behaviors are more docile. The social interactions of this species include vocal, physical, and gestural-visual behaviors. However, these behaviors appear to be more complex than that of their cousin, the common chimpanzee, in that there are few displays of dominance, and many physical displays have a sexual component tied to them. As Frans de Waal and other researchers have found, bonobos and chimpanzees lead significantly different social lives.
In common chimpanzees, females mate only when they produce conspicuous sexual swellings as they come into estrus. This advertises their receptivity to males in the group, who spend much of their time engaging in aggressive behaviors in order to gain mating access to females. Bonobos, however, have evolved a different strategy, in which females are continually receptive. In addition, bonobos use sexual activity as a part of normal social interactions. As such, bonobo groups are more cohesive, with males and females interacting more frequently than is seen in the common chimpanzee, where males rarely interact with females who are not in estrus.
Much of what is known about the behaviors of the closest living relatives of humans has been conducted by researchers such as Jane Goodall, Richard Wrangham, Takayoshi Kano, and Frans de Waal. From their studies, it has been discovered that chimpanzee behavior mirrors that of humans more closely than previously thought. For example, Goodall discovered that chimpanzees engage in war to expand their territory and eliminate any competitors. Goodall also found that chimpanzees are capable of producing rudimentary tools to crack open nuts or fish for termites. However, these behaviors are not universal among common chimpanzees. Rather, each localized population possesses its own suite of behaviors, including toolmaking. This has led some researchers to suggest that chimpanzees possess culture in the human sense.
Based on studies of bonobos, it has been found that humans are not unique in engaging in sexual activity for pleasure. Bonobos have also demonstrated an exceptional ability to grasp complex tasks, such as learning a rudimentary language, which is also shared by common chimpanzees but not to the same degree of proficiency. The capacity of both species for learning may relate to their ability to engage in deception and other cognitive tasks that require associative processing above the reactionary responses seen in other primate species. These and other ongoing studies continue to demonstrate that many of the features once thought unique to humans have their origins in their closest living relatives, the chimpanzee and bonobo.
- Boesch, C., Gottfried, H., & Marchant, L. F. (2002). Behavioural diversity in chimpanzees and bonobos. Cambridge: Cambridge University Press.
- Goodall, J. (1986). The chimpanzees of Gombe: Patterns of behavior. Cambridge, MA: Belknap/Harvard University Press.
- Wrangham, R. W., McGrew, W. C., De Waal, F. B. M., & Heltne, P. G. (Eds.). (1996). Chimpanzee cultures. Cambridge, MA: Harvard University Press.