New research challenges the idea that having many friends means shallow ties. Instead, our brains may be wired to trust and cooperate more as our social networks grow, shifting how we judge reliability in others
Picture the coworker who seems to know everyone, or the friend whose phone never stops buzzing. For years, the assumption has been that people with sprawling social circles are less trustworthy—spread too thin, juggling too many shallow connections. But new findings from the RIKEN Center for Brain Science in Japan suggest the opposite: the bigger the group, the more our brains lean toward cooperation, not betrayal.
In a study published December 23, 2024, in Communications Psychology, researchers had 83 adults play a networked version of the prisoner's dilemma, with groups ranging from two to six. The results were clear: as the group size increased, so did the rate of cooperative decisions, reaching 57% overall. This pattern hints at why people surrounded by many friends or colleagues often come across as reliable—even if, in reality, trust is always more complicated than it looks from the outside.
Classic social psychology has long warned that larger groups dilute responsibility, making it easier for individuals to betray trust. But the RIKEN team, led by Rei Akaishi, wanted to test this in a setting closer to real life, where people can choose their partners and cut ties with those who act selfishly. Over 180 rounds, participants could drop anyone they saw as too self-serving. The data showed that as the pool of potential partners grew, so did the willingness to cooperate. The key wasn’t group size itself, but how the brain manages memory: when it becomes hard to recall exactly who betrayed whom, strict tit-for-tat strategies fade, and people default to a more forgiving, prosocial approach.
To see what was happening in the brain, the researchers used functional MRI with 26 participants. They found that the fusiform gyrus and precuneus tracked memories of past interactions, while the nucleus accumbens linked those memories to the reward of cooperation. The prefrontal cortex—especially its dorsolateral and dorsal anterior cingulate regions—helped decide whether to give someone another chance. When memories blurred, the brain nudged people toward leniency, likely as a way to keep group harmony intact. This built-in bias toward cooperation may be what allows us to function in large, complex social networks, where tracking every slight is impossible.
In daily life, seeing someone with a wide network sends a subtle but powerful signal: many people are willing to keep interacting with them, suggesting a track record of cooperation. It’s a kind of social proof. If someone maintains many connections without frequent fallouts, moves easily between groups, and isn’t routinely excluded, we infer they’re trustworthy enough for others to stick around. This echoes findings from other research, such as the observation that certain private habits can make people stand out in public settings—a topic explored in this analysis of what makes some individuals unforgettable in group dynamics.
For workplaces, schools, and online communities, these insights matter. Allowing people to form and adjust connections freely, rather than locking them into rigid groups, may foster the kind of default cooperation seen in the study. That doesn’t mean small circles are a problem—quality of connection still counts, and the research was limited to small groups of young Japanese adults in a lab setting. The authors plan to expand their work to real-world environments, aiming to understand how culture, leadership, and personality shape group behavior and to develop practical strategies for building more harmonious, productive communities.
Social trust is a complex, layered phenomenon. While group size can influence how we judge reliability, the underlying mechanisms involve memory, reward, and the brain’s drive to maintain social harmony. As our networks grow, we may become more forgiving—not because we’re naive, but because our brains are wired to keep the peace when perfect recall isn’t possible.
One area that continues to draw attention in psychology is the science of social connection and trust. Researchers are exploring how group dynamics, memory, and emotional intelligence interact to shape our willingness to cooperate or withdraw. Understanding these patterns is crucial not just for personal relationships, but for building healthier teams, communities, and workplaces. As studies like this one show, the signals we send and receive about trustworthiness are often more nuanced—and more deeply rooted in our biology—than we realize.
