How many friends can a person actually maintain?

Anthropologist Robin Dunbar proposed that humans can sustain roughly 150 stable social relationships, a limit he linked to the size of the neocortex across primate species and supported with observations of human group sizes from hunter-gatherer bands to military units to village populations. Inside that 150, Dunbar's research describes nested layers that scale by roughly a factor of three: about 5 people in the innermost circle of intimates, around 15 close friends you would turn to in crisis, roughly 50 good friends, then the outer 150 of people whose relationship you actively maintain, with looser layers of 500 acquaintances and 1,500 recognizable faces beyond that.

The number has been challenged, and the criticism is worth taking seriously: later studies using different statistical methods have produced much wider ranges and argued the neocortex correlation is weaker than claimed, so 150 should be treated as a rough order of magnitude rather than a hard ceiling. What holds up better than the specific figure is the structural insight, that friendships are constrained by time and cognitive effort and arrange themselves into concentric layers, so investment in the inner circles necessarily comes at the expense of the outer ones. That has a real implication for social media, where thousands of connections do not translate into more actual relationships, since the binding constraint is the attention and time each bond requires, and adding contacts does not add hours to the week.