Evidence base
Annals of Human Biology
The Social Brain Hypothesis -- Thirty Years On
What it found
This review, authored by Dunbar himself, revisits thirty years of evidence for and against the social brain hypothesis, which links primate neocortex size to social group size. Rather than restating the headline claim, it weighs the accumulated support and the challenges raised against it.
Why it matters for practice
Useful as a corrective for anyone citing the "Dunbar's number" claim as settled fact: it comes from the theory's originator and surveys where the evidence has held up and where it hasn't, which matters for programme design work that leans on group-size heuristics.