Up to 150 relationships: Dunbar's number and the ideal community size

The 150-person wall

In a 1992 paper, the British anthropologist Robin Dunbar showed that there is a correlation between the size of primates' brains and the size of their groups. Species with a larger neocortex live in larger groups. When this relationship is applied to humans, the number of social relationships a person can stably maintain comes out to about 150. This is "Dunbar's number."

Dunbar further showed that these 150 people form layers arranged in concentric circles. The innermost 5 people are close supporters. The next 15 are close friends. The layer of 50 is friends. And 150 is the upper limit of "people whose faces you can match with their names and whose relationship to you you keep track of."

What's interesting is that this structure doesn't change even when your social media followers grow into the thousands or tens of thousands. Even if you have 10,000 followers on Twitter, the people you regularly interact with stay at around 150. Follower count is a measure of "how well known you are," not a measure of "relationships."

The value of the "weak ties" a question box creates

In a 1973 paper, the sociologist Mark Granovetter proposed the concept of "the strength of weak ties." His finding was that acquaintances (weak ties) more often bring new information and opportunities than close friends (strong ties) do.

A question box is a device that efficiently creates these weak ties. An anonymous sender may not be a close friend inside your Dunbar's number. But they are interested in what you share, enough to send you a question. This sense of distance, "interested but not close," is exactly what a weak tie is.

Questions from weak ties often contain viewpoints that wouldn't come from close friends. Close friends know you well, so the range of their questions is limited. On the other hand, senders who are weak ties know only one side of you, and precisely because of that, they throw questions at you from unexpected angles. Questions that make you think "I've never thought about that" mostly arrive from weak ties.

The reality of 10,000 followers and 10 questions

You have 10,000 followers, yet when you open a question box, only 10 questions come in. Many people are disappointed by this situation, but from the viewpoint of Dunbar's number, it's completely normal.

Of your 10,000 followers, the people who regularly see your posts number a few hundred at most. Even fewer of them notice that you have a question box, and only a tiny portion of those who notice actually act on it and decide to send a question. Sending a question carries a psychological cost, so people don't do it without a certain level of interest and motivation.

Those 10 questions were sent by the 10 people out of 10,000 who have the strongest interest in you, after getting past that psychological cost. These 10 people could become the core of your community. In the long run, improving the quality of your conversations with these 10 people leads to more community growth than chasing numbers.

What research on Dunbar's number shows is that human social cognition has limits. Within those limits, a question box is a tool well suited to building relationships that are "few in number but high in quality."

Inviting people into the inner circles

If you think in terms of Dunbar's concentric circle model, exchanges in a question box move the other person from an outer layer to an inner one.

The first question is sent from the layer of 1,500 "people you only know by face." When you answer that question carefully, the sender enters your layer of 150. If the exchanges continue, they move closer to the layer of 50 friends, and if even deeper conversations develop, they move closer to the layer of 15 close friends.

This process is essentially the same as building relationships face to face. The differences are that anonymity lowers the first hurdle, and that because it's text-based, you can interact asynchronously. For busy people today, being able to deepen relationships asynchronously is a big advantage.

Making your question box answers public has one more effect. A third person who sees the conversation between you and the sender recognizes that "this person answers questions carefully" and thinks about sending a question too. One conversation draws in new conversations. This is a dynamic of relationship building that is unique to online spaces and hard to get face to face.

The richness of a small community

In the world of social media, numbers like follower counts and like counts tend to be given a lot of weight. But the idea of Dunbar's number suggests that a sense of social fulfillment depends on the "quality" of relationships, not their "number."

Even if you have only 150 followers, if you're having deep conversations with 10 of them through your question box, that is socially richer than having 10,000 followers and not talking with anyone.

A question box isn't a tool for broadcasting information on a large scale. It's a tool for building up one-on-one conversations within a small community. Each of those conversations invites people into the inner circles of Dunbar's model and enriches your social world.

Don't chase numbers, and face the one question in front of you with care. That is the most natural form of communication for humans, as evolutionary psychology teaches us.