Dunbar's Number and Dunbar's Layers

[lpetrich]

This Is How Many Friends You Need to Be Happy (Lifehacker) referred to work by Robin Dunbar on human social groups -- Neocortex size as a constraint on group size in primates (Journal of Human Evolution, 1992) and Coevolution of neocortical size, group size and language in humans (Behavioral and Brain Sciences, 1993). The neocortex is a relatively recent part of mammalian brains, and it is about 4/5 of our brains.

Robin Dunbar found the best fit to the ratio of neocortex size to the size of the rest of the brain. His fit:
log10(social-group size) = 0.093 + 3.389*log10(brain-size ratio)

Using our number, 4.1, he found 148, usually rounded off to 150. That is Dunbar's number, the number of people that we can keep track of in our minds. This is an average figure, because the actual number typically varies between 100 and 250.

However, we will be emotionally closer to some of these people than to others, and that gives us "Dunbar's layers", how many people have a minimum level of closeness to us. The cumulative layer sizes:

• 5
• 15
• 50
• 150
• 500
• 1500

[1604.02400] Calling Dunbar's Numbers is some recent research using data from cellphones on how many calls each user makes to other users. That research finds somewhat smaller numbers for Dunbar's number and below, but within the natural range of variation. The first one, very close friends, is typically 3 to 5.

 

[bilby]

Armed forces organization reflects this; The 'Dunbar's Layers' map pretty well to:

Fire team
Squad/Section
Platoon
Company
Battalion
Regiment

A Captain might reasonably be expected to know on sight every man in his Company; A Colonel would rarely be able to achieve the same feat with every man in his Regiment.

 

[lpetrich]

Yes, hierarchies are a good way of getting around Dunbar's number, though at the price at introducing more impersonal sorts of social organization.


I'm reminded of Plato's Republic, his proposed utopia. In it, children would not be raised in families, but instead communally, and people would call elders parents and younger ones children. Aristotle objected that “love will be watery…How much better it is to be a real cousin of somebody than a son after Plato's fashion!”

 

[Politesse]

I'm reminded of Plato's Republic, his proposed utopia. In it, children would not be raised in families, but instead communally, and people would call elders parents and younger ones children. Aristotle objected that “love will be watery…How much better it is to be a real cousin of somebody than a son after Plato's fashion!”

There are societies in which this is the case, more or less. Many cultures that practice ambilineal kinship have only generational variations in kin names, and in practice often extend kinship or at least nominal kinship to just about everyone they recognize as part of the community. It would considered rude not to address an elder as "grandmother" or "grandfather" in traditional Hawaiian or Tuareg society, for instance.