So many people think that the more Facebook friends they have, the better. Wrong! In an excerpt from his just released book You Are Not So Smart David McRaney explains "Dunbar's Number" and why trying to keep in touch with more than 150 people, even on Facebook, is a biological impossibility.

The Misconception: There is a Rolodex in your mind with the names and faces of everyone you've ever known.

The Truth: You can only maintain relationships and keep up with around 150 people at once.

In other primates, social relationships are maintained by grooming-picking bugs off of each other. You don't go to a Mad Men party and dig around in your friend's hair while watching the show. But getting together for any reason is still a grooming behavior. Visiting friends just to shoot the shit is the human equivalent of picking ticks off of each other's backs. As technology has allowed you to be farther and farther apart yet still keep in touch with loved ones, your grooming behavior has remained constant.
But you can't keep up with all those people and their connections, not in a real social way. Out of this cluster of humans you can only reliably manage to keep up with around 150 people. Giant cities full of other humans, Internet social networks with hundreds of people sharing status updates, corporations with branches around the world-your brain is incapable of handling the multitude of human contacts populating these examples.

Why is this?

The neocortex of primates is the part of the brain responsible for keeping up with others. We can't be certain of what forces shaped the size of this part of the brain, but for each primate the size of the cortex correlates with the size of the average social group. Apes live in small groups, humans live in big ones. Robin Dunbar, the anthropologist who first presented this concept, figures the size of the average group is directly correlated with how efficiently the members can socially groom one another. Dunbar says that efficiency is predicted by how large the primate's neocortex is. According to Dunbar, the larger the group, the more time must be spent by each member to maintain social cohesion. Each person must do some grooming with each other person, and then also keep up with who is friends with whom, who has a beef, what their relative status is compared to yourself and others and other to others. The complexity builds exponentially with each new member. If someone you know moves away, you start to groom them less and less until you start to touch base once a year, or maybe lose touch for years. It takes far more effort to stay connected once a friend escapes your direct contact. That effort takes away from the time you can spend with other friends. There is a maximum amount of time and effort you can spend-it is a zero-sum system.

Sure enough, all the sciences which study tribes, bands and villages have approximated ancient groups usually maxed out around 150 people. This is the approximate upper limit to how many people you can trust and count on for favors, whom you can call up and have a conversation with. Once you go over 150 people, Dunbar says about 42 percent of the group's time would have to be spent worrying about each other's relationships. Dunbar's number explains why big groups are made of smaller, more manageable groups like companies, platoons, and squads-or branches, divisions, departments, and committees. No human institution can efficiently function above 150 members without hierarchies, ranks, roles, and divisions.

Dunbar's number isn't fixed. It can be increased or decreased depending on the environment and tools you have available. You most likely have a much smaller group of friends than 150 people, but when you are incentivized to connect to more people than you would naturally associate-like at your job or in a school-150 is the point where your neocortex cries uncle. With better tools-like telephones, Facebook, World of Warcraft guilds and so on, you become slightly more efficient at maintaining relationships, so the number can be larger, but not much larger. Dunbar's most recent research suggests even power-users of Facebook with 1,000 or more friends still only communicate regularly with around 150 people, and of that 150 they strongly communicate with a group less than 20.

The social web is revolutionizing the way institutions operate, and the way people communicate, but in the end it might not have much of an effect on the core social group you depend on for true friendship. You can maintain a giant number of weak ties to people on Facebook, Twitter, and whatever comes next, much like you can in a giant company. Strong ties, however, require constant grooming. Anyone who uses the number of friends they have on Facebook as a metric of their social standings is fooling themselves. You can share videos of fainting goats with hundreds of acquaintances and thousands of followers, but you can only trust a secret with a handful of true friends.

Excerpted from "You Are Not So Smart" by David McRaney with permission from Gotham Books.

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