4 for conversation

[After study] the first thing we found was that conversation groups are not infinitely large. In fact, there appears to be a decisive upper limit of about four on the number of individuals who can be involved in a conversation. The next time you are at a social gathering such as a reception party, take a look around you."

"You will see that conversations begin when two or three individuals start talking to each other. In due course other individuals will join them one by one. As each does so, the speaker and listener will try to involve them in conversation, directly commenting to them or simply moving to allow them to join the circle. However when the group reaches five people, things start to go wrong. The group becomes unstable. . .despite all efforts (and groups often do try), it proves impossible to retain the attention of all the members. Instead two individuals will start talking to each other, setting up a rival conversation within the group. Eventually they will break away to start a new conversation group."

from "Grooming Gossip and the Evolution of Language" by Robin Dunbar