Tonight (Thursday) on Catalyst Dr Jonica Newberry is going to show a segment entitled Falling in Friendship (cf falling in love), which will look at Dunbar’s number, the number of friends we can maintain in an enduring relationship. The Wikipedia spiel is as follows:
Dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is and how each person relates to every other person.
This number was first proposed by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. By using the average human brain size and extrapolating from the results of primates, he proposed that humans can only comfortably maintain 150 stable relationships. Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. It has been proposed to lie between 100 and 250, with a commonly used value of 150. Dunbar’s number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.
Dunbar theorized that “this limit is a direct function of relative neocortex size, and that this in turn limits group size … the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained.” On the periphery, the number also includes past colleagues, such as high school friends, with whom a person would want to reacquaint themself if they met again.
Dunbar himself identifies trust and obligation as key elements in the relationships he is talking about. He cites the Domesday book as showing village sizes to cluster around 150 in 1086. He also sought evidence from parishes in the 18th century and from hunter-gatherer societies. On hunter-gatherers:
Dunbar noted that the groups fell into three categories — small, medium and large, equivalent to bands, cultural lineage groups and tribes — with respective size ranges of 30–50, 100–200 and 500–2500 members each.
Francis Fukuyama in his book The Origins of Political Order suggests that politics starts to become formal at the level of the tribe. Yuval Harari in Sapiens suggests that anthropologically groups tended to divide if they exceeded 150.
In military terms, 150 seems to be the ideal company size, historically and at present.
The first thing to note is that Dunbar himself considered the number exploratory due to the large error measure (a 95% confidence interval of 100 to 230).
People will ask, What about Facebook?
The obvious answer is that Facebook allows a large number of weak relationships to be maintained. It also maintains relationships that may otherwise lapse through distance. The suggestion is that it doesn’t radically alter Dunbar’s number.
Clearly, also, more relationships can be maintained if people spend more time on social grooming.
Alternative numbers have been suggested, but so far Dunbar’s number seems to hold sway.