Human Hardware: Dunbar’s Number

Just Behave - A Column From Search Engine LandFew things about the internet generate as much buzz as social networking. Suddenly, it looks like the very fabric of our society might be rewoven online. The world becomes our community as we erase geographic boundaries to connect based on shared interests and ideals. Whether your community of choice is Facebook, MySpace, Second Life, or LinkedIn, it seems that we are rewriting the rules of friendship and acquaintance.

Or are we? While the technological impediments have been removed, are there limits imposed by the hardwiring of our brains? Is there a human hardware limit on how many friends we can have? In this column, I want to start to answer this question by looking at our evolutionary past, and how our social networks have evolved. In Part Two, I’ll explore what happens when you take our inherent social abilities and move them online.

Metcalfe’s Law

Perhaps you’ve heard of Metcalfe’s Law, which states that the value of a telecommunication network is proportional to the square of the number of users of the system. So, when there were only one fax machine in the world, the value of this network was essentially zero. There was no one else you could fax to. If you expand the network to 10 fax machines, the value of the network expands dramatically, because now not only are there 9 more people you can fax to, but they can all also fax to each other. Each time new users are added, the value of the network increases proportionately.

Metcalfe’s law makes sense technically, but there are some challenges from a human perspective. Networks are only as valuable as the number of people you really want to connect with. Everyone may have a fax machine, but that doesn’t mean you want to fax everyone. From a macro perspective, the value of the network may increase substantially based on the number of users in the network, but from a micro perspective, yours, the value of the network is determined by how close you are to the people in the network and how valuable they are to you.

Dunbar’s Number

This brings us to a rather fascinating concept called Dunbar’s Number. Robin Dunbar is a British anthropologist that studied the relationship between neocortical size in primates and the size and complexity of their social networks. He found that the number of social relations we can successfully maintain is limited by the size of our neocortex. There are cognitive limits to how many friends and acquaintances we keep track of. To maintain an active social relationship, even on an occasional basis, requires that we keep some information about each of those people. You have to maintain an inventory of personal information in order to grease the social wheels. For example, transactive memory is one of the benefits that comes from these social networks, but for transactive memory to work in traditional social groups, you have to know everyone well enough to know what they may know. Dunbar looked at different primates, including humans, and, using regression analysis across all their network and cortex sizes, predicted that the human social “inventory” limit should be about 150.

Next, Dunbar looked for evidence of these limits in our modern world and in the few existing hunting-gathering cultures, remnants of our evolutionary past. Now, most hunter/gatherer societies are not that concerned with accurate census information, so Dunbar found it difficult to get the data needed for comparison, but he found that when he averaged what he had, based on functional groups (a mid-level grouping that fell between hunting parties and tribes) where there were strong social ties between members of the group, he found the average size was 148.4. Even when he examined variations, there was a remarkable consistency in findings right around his predicted 150 value.

Next, Dunbar looked for examples in the modern world. Hutterites, a fundamentalist sect that live in farming colonies, have a limit of 150 members, after which the colony breaks up into 2 daughter colonies. In academic disciplines, once a research specialty attracts much more than 200 active researchers, it tends to naturally split into sub-disciplines. And most organized armies naturally evolve into a basic unit of 150 men.

The Great Leap Forward

One of the greatest mysteries of our human history is why, for hundreds of thousands of years, although the human brain had achieved its current size and structure, there was little to differentiate us from other animals. Then suddenly, about 50,000 years ago, humans suddenly went from using crude stone tools and living much like the other animals we shared the earth with to creating complex civilizations, art, intricate tools, and eventually science and technology. All of this happened in the blink of an evolutionary eye. Why, for so long, were we stuck in an evolutionary rut and then, suddenly, leapt ahead of every other species on earth? What was the spark that caused this?

A portion of the answer can be found in Dunbar’s Number, as well as the work of others including Jared Diamond and Steven Pinker. The theory is that our sudden rise came from our ability to maintain complex social networks. There were safety in numbers, leading to an evolutionary advantage that soon caused humans to flourish.

But there’s an investment required to maintain social networks. As Dunbar found, the larger the neo cortex and the bigger the social network, the more time that primates devote to social grooming. In non-human primates, grooming is the social glue that holds the community together. The more time devoted to grooming, the more cohesive the community. And grooming is not a universally applied practice. Rather, Dunbar found that as group size increased, the intensity of grooming between “special friends” or the closest connections in the community increased. To put it in marketing terms, it wasn’t the reach that increased, it was the frequency.

The human neo cortex, by far the largest amongst primates, allowed us to invest in the grooming required to grow our networks to the predicted cap of 150 people. But a larger neocortex still doesn’t explain the great leap. Our neocortex has been approximately the same size for the last 250,000 years. Why, in the last 50,000 of that, did our society suddenly evolve from living in caves and throwing rocks at woolly mammoths to flying to the moon, nano technology, and Beethoven’s Fifth? What enabled the Great Leap?

The answer comes when we look at the cost of social grooming. How much time must we invest in maintaining the social glue required to keep the network together? In looking at primates, Dunbar found that a group of baboons dedicated the most time to grooming, with almost 19% of their time spent maintaining their social connections. But, projecting the same percentage for humans simply by the size of our neo cortex alone would require us to spend 42% of our time grooming to maintain cohesion in a network of 150 members. While groups gave humans a evolutionary advantage, if it took almost half our time simply maintaining the group, we wouldn’t have enough time to devote to the other aspects of survival, such as raising offspring and finding food. We certainly wouldn’t have time to paint a picture or write a symphony.

Language and Social Bonding

No, the answer to the Great Leap comes, it is now believed, from the appearance of language. Prior to language, we had to be face to face to understand enough about a person to maintain a social relationship with them. We picked up their feelings through facial expressions and body language. Grooming facilitated this communication through the need for physical proximity. But language dramatically changed the game.

With language, we could express feelings more efficiently, cutting down the requirements for grooming. We could maintain cohesion with a smaller investment of time. And, perhaps most importantly, we could extend social knowledge and communication beyond the boundaries of face to face communication. Language allowed for gossip, which is probably the modern activity most closely related to its evolutionary roots. More nobly, language allowed for planning, strategy, creation, and transference of knowledge. Groups could interact more effectively, and the wisdom collected by one generation could be effectively passed on to the next. For the first time, humans didn’t have to start over from scratch with each successive generation. Knowledge accumulation could be incremental.

But language isn’t everything. While language allowed us to reach beyond face to face boundaries, we still rely heavily on facial expression, body language, and other non-verbal cues to communicate, especially when it comes to feelings and emotions. When we’re making the choice whether or not to admit someone to our social network, we have to make a decision whether we’re willing to commit the “grooming” time required. The closer they want to be to us, the bigger the commitment and, subsequently, the higher the risk. And this is simply not a call we’ll make without the benefit of face to face communication. We need to judge whether this person is honest, trustworthy, and sincere. You can’t do that at arm’s length.

Today, I’ve laid out the human hardware foundations for social networks. The question I’ll deal with in the next column is what happens when you move this online. Is Dunbar’s number obsolete, or does it hold up online as well? And what will happen with your own social networks as technology increasingly becomes the channel you communicate through?

Gord Hotchkiss is CEO of Enquiro, a search marketing firm that produces search engine user eye tracking studies and other research. The Just Behave column appears Fridays at Search Engine Land.

Opinions expressed in the article are those of the guest author and not necessarily Search Engine Land.

Related Topics: Channel: Content | Search & Usability


About The Author: is CEO of Enquiro, a search marketing firm that produces search engine user eye tracking studies and other research.

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