Friday, January 13, 2012

Dunbar's number

The Dunbar's number is, according to the anthropologist Robin Dunbar, the theoretical cognitive number of individuals that can develop fully in a given system. He theorizes that this value (of approximately 150 individuals), its related to the size of the brain neocortex, and his processing capacity.
The primatologists noted that because of their highly sociable nature the non-human primates have to maintain personal contact with the other members of his social group. The number of members with who a primate can maintain said contact seems to be restricted by the size of the neocortex, and that suggests that there is an index of group size relative to the specie. So in 1992 Dunbar used the correlation observed in primates to predict the size of the social group in humans. He predicted a size of 147.8 group members, usually represented as 150.
Dunbar compared this prediction with observable human groups and noted that the groups fall in three categories, of 30-50, 100-200, and 500-2500.The research of Dunbar on the size of tribes and villages seemed to corroborate his prediction: 150 was the estimated size of a village farmer of the Neolithic; 150, as the point of break and separation of a hutterite settlement and 150 as the basic size of a military unit in ancient Rome and in modern times since the 16th century.
Dunbar theorized that a group with a size of 150 persons needs to have a very high incentive to stay together, thus 150 members groups only occur due to an absolute necessity, for example, aggressive economic pressure. For a group this size to maintain such cohesion, he speculated was needed to dedicate a 42% of the time to socialization; a dispersed group would have fewer ties, meeting less frequently.
Dunbar proposed also that the language may have generated as an easy way to socialize, because without language the humans would have had to occupy almost half their time socializing; the language may have allowed societies to remain cohesive, reducing the need for physical and social intimacy.
It's considered that -according to Dunbar's theory- in small-scale (less tan 150 individuals) most social orders could function properly, but due to population growth, problems arise due to the difficulty of maintaining properly controlled relations between individuals. This theory also applies to problems of overpopulation, because the further away a group moves of the hypothetical limit of 150 in any delimited system, its more likely for conflict to grow.

10 comments:

  1. Very interesting.....thats probably what happened to the Roman Empire, it was so big that it collapsed.... And I guess we have to face this problem in the future due to over population.

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  2. Why may the groups fall in 30-50, 100-200, and 500-2500? I wonder. I think it very strange o.O

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  3. @Gialu: Over population shouldnt be a big problem in the futures because with growing income, the reproduction rate of a nation decreases.

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  4. 150 seems to be alot; which is reflected by the percentage needed to maintain the group size (42%!!!). I find that to be an astronomical percentage of time when you try to think about it in terms of what that actually means especially when factoring in how much time is dedicated to sleep. This would leave little time for much else. good post.

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  5. The grouping does seem a little out... as a psychological experiment, this lacks validity, and as for sociology, I'm pretty unsure...

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  6. I would say that every person needs about 3 friends or he may go crazy.

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  7. Great article! Keep up the good job!

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