Perspectives in Leadership and Group / Cohesion Survival

Social Cohesion by the Numbers – Dunbar’s and the Allen Curve

Executive Summary:

The building blocks of a powerful and successful cohesive societal unit are a combination of the theorems below:

Careful observation will detect a clearly emerging pattern of basic human nature and how it affects a cohesive team. As with other theorems of sociological research Dunbar's number is not a singular factor but one more arrow in our quiver.  No single theorem stands alone. Together time-tested and well vetted theorems help us to develop better ways the build more cohesive teams. These tools apply in every form of human interaction from clubs and clans, to military units and societies.

Dunbar’s rule states that when societies/groups exceed 148 members bad things begin to emerge in the social interactions. Violence, sexual perversions, deceit, theft, and much more tear apart the sub-148-member group’s previously peaceful tranquility.

Even if you do not wish to lead,
you must understand the theorems
listed above if you wish to survive.

that Dunbar’s Number plays an important part in the crafting of cohesive social unit. Understanding the significance of the causality and effect of Dunbar’s number is the very important. The postulated cognitive limit to the number of people with whom a person can maintain stable social relationships is enlightening.

We see the validation of the Dunbar Number every time that we look at a large urban area. Cities cram many people into very dense units. Crime, violence, and more is evident just as in the studies. Yet in the plans put forth by many planners, including the UN, they plan to jam 80% of the world’s population into 20% of the land.

Ignorance to Dunbar’s number and the other correlated theorems will not change the outcome. 200,000 years of historical data prove that Dunbar’s number is a good starting point. The 80/20 plan will yield only one possible outcome, the need for more policing, government regulation, oversight, and controls. The crime, violence, and antisocial behaviors associated with such high-density populations is intense. I am writing an article on my idea of "Mesh Network Societies", stay tuned.

Despite the ubiquitous use of technology, Dunbar’s Number is bolstered by the Allen Curve which demonstrates a massive drop in communication between group members as the distance between them increases. Conversely, if they spend time in the presence of a person they are likely to keep in contact via other means when they are apart, short term.

There are many lessons to be learned for leaders. If you are not a leader, knowing the signs of good leadership and the earmarks of a solid cohesive unit will help you to choose wisely with whom you align yourself for the best survival results.

Body - Supporting Material:


British anthropologist Robin Dunbar, first posited his research findings in 1992. He discovered a correlation between primate brain size and the mean average size of their social group. In his paper, "Co-Evolution of Neocortex Size Group Size and Language in Humans”, he hypothesized a predictive mean group size for humans (Dunbar’s Number) at 147.8.  Dunbar studied census evidence, spanning from the Pleistocene humans 200,000 + years ago through the present time. His theorem, known as the Dunbar Number, is based upon research studying primate groups, primitive human villages, cultures, and tribes.

The research focused on neocortex size and its relationship to a perceived cognitive limit related to the number of individuals with whom anyone person can maintain stable relationships. While language played a part in the social group and its cohesion, primatologists and sociologists observed some troubling results when the numbers rose over 138.  Testing with both non-human primates and humans Dunbar discovered Dunbar's number, a 95% confidence interval of between 100 and 230. Dunbar believed after all his research that the optimum / “sweet spot” predicted “mean” social group number for humans was 148.

Research focused on defining the building blocks of successful social unit cohesion; what makes a group/clan/society survive and succeed as a unit together. Anthropologists, linguists, engineers, technologists, primatologists, sociologists, and many others have tested, studied, and studied the phenomena and always prove out Dunbar’s number. There is a voluminous amount of peer reviewed research supporting Dunbar. We, as did countless researchers, see innumerable examples of this in play all around us.

Dunbar's number has been popularized in countless business and management books around the world.  Creative license has popularized Dunbar's number as 150.  The number is often referred to as the tipping point.

One of the most intriguing stories that Malcolm Gladwell related in his book; “The Tipping Point” was about the company who manufactures Gore-Tex. The company, in an effort to increase profit and efficiency, discovered through a process of elimination, that Dunbar’s Number was the key to their quest. They broke their workforce up into 150-person groups. Each building housed 150 employees, as they said, “Each time the 150 parking spots were filled, we built another building”. They were highly successful.

Surveys of village and tribe sizes validate that nearly all Neolithic farming villages, Hutterite settlements, and even professional armies in Roman antiquity limited themselves to 150 as the basic unit size. This was not a coincidence.

The Allen Curve, developed by an MIT Professor Thomas J. Allen, is a graphical demonstration of how the level, quality, and frequency of communication decreases exponentially between people as the distance between them increases. The Allen Curve supports the Dunbar Number. In fact, in Allen’s book (co-written with G. Henn) entitled “The Organization and Architecture of Innovation: Managing the Flow of Technology” they revisited the Allen Curve years later in 2006 and found the following:

  • "For example, rather than finding that the probability of telephone communication increases with distance, as face-to-face probability decays, our data show a decay in the use of all communication media with distance (following a "near-field" rise)." [p. 58]
  • "We do not keep separate sets of people, some of whom we communicate with by one medium and some by another. The more often we see someone face-to-face, the more likely it is that we will also telephone that person or communicate by another medium." [p. 58]

For extra credit reading, check out Peace Among Primates, written by Robert M Sapolsky Ph.D. at Stanford University. Specifically focus on the section regarding natural born killers. (There is a well written article on the book, click here to read). In the article entitled “Why are people brutal?” I explain some of the other factors that are enhanced or out rightly provoked by exceeding the Dunbar Number. (Click Her to read “Why are people brutal?”)

Closing Statement:

There is no silver bullet when it comes to forming a cohesive unit or society. Humans are complex creatures with countless underlying propensities, strengths, and deficiencies. No single theorem stands alone. Together they may serve as arrows in your quiver. As a planning strategy, these time-tested and well vetted theorems can help us to understand and develop better and more cohesive teams. They are tools applicable in every form of human interaction from clubs and clans, to military units and societies.

As stated in the body of this article, the following theories and rules may act as building blocks in the formation of a powerful and successful cohesive unit / society:


"Co-Evolution of Neocortex Size Group Size and Language in Humans”

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