lpetrich
Contributor
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:
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