"The Social Brain: The Psychology of Successful Groups" by Tracey Camilleri, Samantha Rockey, and Robin Dunbar explores the hidden patterns behind human connection and how they shape successful teams, organizations, and communities. Drawing on insights from psychology, evolutionary anthropology, and neuroscience, the authors argue that our capacity for social connection is biologically limited but profoundly powerful. Whether in a business setting or a close-knit community, the ways we form bonds, build trust, and synchronize with others significantly impact both individual wellbeing and group performance. This book brings together scientific research and real-world examples to reveal the mechanisms that allow groups to thrive—or falter—based on the quality of their social relationships.
At the heart of the book lies the idea that humans are neurologically equipped to manage only a certain number of meaningful relationships. This number, approximately 150, is known as Dunbar’s number, based on the research of Robin Dunbar himself. This limit appears consistently across cultures and time periods, from prehistoric tribes to medieval villages to modern corporations. Even on social media platforms, people maintain genuine interactions with a similar number of individuals, suggesting a deep-rooted biological constraint. The brain areas responsible for processing social information, such as the frontal and temporal lobes and the limbic system, have limited capacity, which naturally caps the number of relationships we can sustain. Beyond this threshold, group cohesion weakens and coordination becomes more difficult.
This numerical limit is not arbitrary; it reflects an intricate social architecture. People organize their social world in concentric layers. Closest to the center are about five individuals we deeply rely on, followed by a slightly larger circle of around fifteen, often those whose loss would affect us emotionally. A group of fifty forms the wider network of regular interaction, and finally, the broader layer of 150 encompasses all meaningful social ties. These natural groupings serve practical purposes. For example, small work teams of fewer than five members often achieve more effective communication, greater trust, and higher productivity. Research into software development teams shows that smaller groups outperform larger ones by avoiding the communication delays and decision-making complexity that come with size. Similarly, elite military units operate in teams of four or five to maintain tight coordination and deep mutual trust.
Real-life communities also exhibit this pattern. Hutterite settlements, for instance, deliberately split into new communities once they exceed around 150 members. After surpassing this size, social friction increases, cooperation declines, and collective motivation weakens. By returning to optimal group sizes through splitting, they restore harmony and shared purpose. This practice has remained stable for generations and supports the argument that our social limitations are not just cultural but deeply ingrained in our biology. In modern workplaces, scaling organizations without accounting for this natural cap can lead to inefficiencies and morale problems. However, growth need not be avoided entirely. Instead, organizations can be structured as networks of small, interlinked teams that preserve the benefits of intimacy and personal connection while allowing for expansion.
The book emphasizes that the presence—or absence—of human connection dramatically affects mental health, motivation, and workplace performance. A comparison between railway workers and warehouse employees illustrates this point vividly. Though railway workers often face more difficult physical conditions, their shared shifts and opportunities for conversation foster stronger interpersonal bonds. In contrast, warehouse employees working in isolation, guided by impersonal digital instructions, tend to report worse mental health. This effect mirrors larger studies showing that the quality of close relationships strongly predicts health outcomes. In fact, having strong friendships increases survival rates following a heart attack more than most traditional health factors.
These findings align with what is known as the kinship premium: our instinctive bias toward helping and valuing those we feel close to. In professional settings, people who report having a close friend at work show markedly higher engagement and job satisfaction. Gallup’s long-term studies confirm that employees with strong social ties are more likely to contribute creatively, collaborate effectively, and stay with an organization. Microsoft’s research supports this idea as well, showing that workplace relationships fuel innovation and resilience, especially during disruptive events like the COVID-19 pandemic. Companies that nurtured social bonds before the pandemic adapted more successfully to remote work, drawing strength from existing trust networks.
Sometimes, the solution is as simple as designing for more human interaction. In one warehouse case study, management adjusted break times to allow coworkers to spend time together. As a result, employees began coordinating lunch breaks, which led to increased cross-department collaboration and even improved safety records. This outcome reinforces the idea that small design choices can make a big difference when they foster real human contact.
The book also introduces the concept of the Seven Pillars of Friendship: common language, geographic origin, professional background, hobbies, worldview, humor, and musical taste. These dimensions help explain how we form bonds, and research shows that people who share several of these pillars are more likely to develop strong, lasting relationships. Interestingly, teams that share a moderate number of pillars—three or four—tend to perform best. Too many shared traits can lead to homogeneity and groupthink, while too few can hinder understanding. Balanced teams with both common ground and diversity tend to collaborate well and generate creative solutions. Organizations can apply this knowledge intentionally, such as arranging informal gatherings that facilitate discovery of shared interests or designing office spaces that encourage chance encounters.
Another key theme in the book is the power of synchronized activity to deepen social bonds. When people engage in rhythmically aligned behaviors—such as rowing, dancing, or even walking together—their bodies release endorphins, which enhance feelings of trust and connection. This biological response has roots in our evolutionary history, where synchronized movement helped early humans build cohesion and cooperation. The same mechanism is used today in military training, where repeated drills and coordinated actions create unshakable trust among unit members. Theater directors also use synchronization exercises to help casts bond before performances, creating an emotional safety net that fosters risk-taking and creativity.
Workplaces can adopt similar practices. A tech startup that introduced daily communal lunches found that shared mealtimes helped establish a natural rhythm among employees, improving communication and collaboration. These practices don’t require elaborate team-building programs—just spaces and routines that bring people into alignment through shared experience.
Trust is another critical component of successful groups. In tight-knit communities like Amsterdam’s diamond district, transactions worth millions are based on simple verbal agreements, relying on long-standing social trust. However, trust is fragile and can unravel quickly if a few individuals exploit the system. Behavioral experiments reveal how even small breaches of trust can trigger widespread collapse of cooperation. Alarmingly, a tiny proportion of people are responsible for a disproportionate number of lies, which can contaminate an entire network. Yet attempts to solve this problem through excessive monitoring or rigid controls often backfire. Instead of improving accountability, they foster resentment and disengagement.
A more effective approach is to build systems that assume most people are trustworthy and offer them autonomy and responsibility. The Dutch healthcare provider Buurtzorg exemplifies this philosophy. Its nurses work in self-managing teams with minimal supervision but shared accountability. This model not only improves patient outcomes and reduces costs but also boosts job satisfaction. The system works because it trusts professionals to act in the best interests of their clients and each other, reinforcing a positive cycle of responsibility and collaboration.
Ultimately, "The Social Brain" makes a compelling case for rethinking how we build teams, lead organizations, and design workplaces. Human beings are social creatures with clear cognitive limits and emotional needs. Recognizing and respecting these limitations allows organizations to unlock higher levels of engagement, creativity, and resilience. The book’s message is both scientific and humanistic: when we build environments that reflect how people naturally connect, we create the conditions for groups to flourish. By valuing small teams, encouraging shared experiences, and trusting in the goodwill of most individuals, we can cultivate not only stronger organizations, but also healthier, more fulfilling lives.