Science > Social organization of the four apes

Describe the social organization of the four apes. Include in your answer a discussion of the degrees of sexual dimorphism among the great apes and which sex leaves the group at puberty.

Sexual dimorphism can be correlated to behaviors relating to social organization. Sexual dimorphism is greatest in polygynous societies. Primates that live in monogamous societies show a lack of sexual dimorphism in size. I will discuss the social organization and the difference of sexual dimorphism among Gibbons, Orangutans, Gorillas, Chimpanzees and Bonobos.

Gibbons are found throughout Southeast Asian rainforests and often referred to as “the singing ape”. Gibbons live as territorial, single, family groups with three to six individuals, a monogamous pair and up to four offspring. Gibbon pairs stay together for life and their offspring usually stays with them for up to ten years. When the young gibbons become adolescent it usually leaves the family because at this age (four to five years) the same sex parent does not tolerate it in its territory anymore. After the young gibbon looks for a partner and try to develop its own territory. This kind of behavior prevents inbreeding. Gibbons, because of their body size, are termed lesser apes. Their arms are relatively longer than their legs, adapting them to brachiation. Gibbons are not sexually dimorphic females and males are about the same size.

The orangutan is the largest animal in the world that is adapted to living in trees. Sexual dimorphism is marked. Male orangutans are approximately twice the size of females, weighing up to 300 pounds and can reach a height of 5 feet and it may be an adaptation for mating, as strong competition among males for females tends to promote this type of sexual dimorphism. Orangutans have long, narrow hands and feet that is useful for grasping branches.

Female orangutans reach sexual maturity at 9-12, males at 9-15 years of age. Females will not have their first offspring until 13-16 years of age. Orangutans have the longest “childhood” of the great apes. The young stay close to their mothers until they reach adolescent. Females are usually found alone, or sometimes with their offspring. Group living would be a disadvantage because of the large amount of food they need to eat to meet their nutritional needs.

Like most primates, gorillas live in cohesive groups called troops consisting of multiply males and females and their offspring. A group size usually ranges from 2 to 35 individuals; most gorillas live in groups of from 10 to 20. Each social group has a silver back male who plays an important role within the troop by protecting the other members, leading them in search of food and stopping fights and usually it is the only breeding male in the group.

Females tend to leave their native group around the age of 8 and travel between groups. Males leave their natal group at the age of 11 and live solitary until they gain females and are able to start a group of their own. Gorilla troops have reasonably steady memberships, with little movement between troops.

Gorillas, like most primates show marked sexual dimorphism. Adult males can stand six feet tall, the weight can reach 400 pounds in the wild, most adult females are only about 200 pounds and much less muscular.

Chimpanzees live in communities in tropical Africa. Chimpanzees are very social animals and usually live in groups of between 20 and 80 animals. Each group tends to have a dominate male and to a lesser degree a dominate female, but sometimes the hierarchy changes. Communities usually split up into smaller groups and often travel around. These groups are always changing as individuals are on their own for a while, or join other groups. Mothers and their young, up to seven years old are always together. Some other individuals, such us siblings and male friends travel together. Females often leave their group and transfer to a new community permanently. Males hunt cooperatively and share the meat with females. The chimpanzee is known for its use of tools. This is not an instinctive behavior and must be taught to their young. Females are sexually attractive to males at age 10 or 11. Males are capable of reproduction at age 12, but they get socially mature a few years later. When chimps meet they use facial expressions, vocalization and gestures to communicate. Chimpanzees are also highly hostile towards other groups and can attack with extreme brutality. This may result in the death of the victim. Chimpanzees have a low degree of sexual dimorphism. Female’s height about 88 percent of the average male’s height.

Bonobos social organization differs from the great apes. Bonobos are most frequently found in mixed age and sex groups with adults. In the bonobo’s social structure females have the strongest bonds, although females also bond with males, they also clearly in charge. One special feature observed in bonobo society is the low level of aggression between individual bonobos. Their generally peaceful society is attributed to the evolution of a highly complex social system. They developed a set of ritualized socio-sexual behavior that is very typical to this species. They have sex very frequently, sometimes to settle conflict or to get to know each other. Bonobo communities split into groups of 2 to more than 50 individuals. Females leave their original group when they’re grown, migrating into new bonobo societies where they bond with other females to establish a place in hierarchy. A female bonobo gives birth every five or six years, since the infant is dependent on its mother for the first four years of life. Bonobos mature at about 7 to 10 years; females first give birth at age 13 or 14 and are fully grown by 15 years. Females are 85 percent as big as males.

Primates that live in monogamous societies exhibit the following features: a lack of sexual dimorphism in size and coloration. Primates that live in polygymous groups typically show the following characteristics: closely bonded adult females, somewhat socially separate reproductive male; strong intolerance by the reproductive males of other, potentially reproductive males; leadership shown by at least some females in many aspects of group life, while the adult male shows an outward-from-the-group orientation; some turnover in reproductive males.

References:

http://www.homepages.feis.herts.ac.uk/ ~comqcln/al7ev/dautenhahn/node3.html

http://www.zoosociety.org/Conservation/Bonobo/WhatIs.php

http://www.biosci.umn.edu/~pregal/demonic.htm

Conrad Phillip Kottak: Anthropology

 

 

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