It’s called the “dinner party problem”: A table of four or fewer people may happily converse as one, but a party of five or more will splinter fairly quickly into separate conversations of two or three four people each. What is it about the number four?
The question bothered Jaimie Krems, an assistant professor of psychology at Oklahoma State University. Krems had previously studied under Robin Dunbar, the Oxford University evolutionary psychologist who theorized that cohesion in any human social group falls apart once the group reaches 150—a figure now known as Dunbar’s number. But just as the dynamics of large groups start changing around 150, something also happens to the casual conversations of small groups once they surpass four members.
Social psychologists have noted the pattern in group conversations in research stretching back decades. There’s evidence that this four-person limit on conversations has been in place for about as long as humans have been having chatting with one another. Shakespeare rarely allowed more than four speaking characters in any scene; ensemble films rarely have more than four actors interacting at once. But why do we max out at four?
In a forthcoming paper in the journal Evolution and Human Behavior, Krems and Jason Wilkes offer one theory rooted in evolutionary psychology.
Pairs (or “dyads,” in psychology research parlance) are the essential building blocks of a society. Let’s imagine a conversation between four hypothetical humans: you, Chris, Pat, and Taylor. In a four-person conversation, there are six possible pairs of people who can be talking to one another at once. you and Chris, you and Pat, you and Taylor, Chris and Pat, Chris and Taylor, and Pat and Taylor. That’s three pairs you’re part of, and three pairs you’re not. Essentially, you have a role in influencing half of the possible conversations that could be happening in that group.
If there are three people in the conversation, there are three possible pairs, only one of which excludes you. If there are five people, there are 10 possible pairs, and the majority—six—don’t include you, which makes it harder to get your point across.
What if, the researchers argue, there was an evolutionary advantage to not being “outnumbered” in a conversational group? The physical danger of being an isolated outcast is clear: exclusion from society in early human history could easily be a death sentence, and even most observed cases of lethal chimpanzee violence have happened when aggressive groups encounter a lone chimp.
Perhaps there was an advantage in not being a conversational outcast, either. If a group is trying to reach an important decision—the safest location to build a shelter, for example, or how to allocate scarce food—your position has a better chance of prevailing if you’re able to convince at least half of the group. You also have a better chance of being able to talk your way out of exclusion.
“Just as one may have avoided death by avoiding being individually outnumbered in intergroup interactions, then, perhaps one would have been able to avoid social condemnation and/or exclusion by avoiding being dyadically outnumbered in in-group interactions,” they write. Yikes.
It’s possible our brains evolved to manage only the conversations in which we have a chance of swaying the group to our side. Otherwise, what’s the point of talking?