Function: maxGroupSize()

maxGroupSize(neocortexRatio): number

Maximum stable social group size, from neocortex ratio.

Source: Dunbar, R.I.M. (1992). "Neocortex size as a constraint on group size in primates." Journal of Human Evolution, 22(6), 469-493.

log10(N) = 0.093 + 3.389 × log10(CR)

CR is the neocortex volume divided by the volume of the REST of the brain — not by body mass. It runs about 1.5 in small primates and 4.1 in humans, where this yields 148: Dunbar's number, reproduced from his own regression.

The ported PEER_REVIEWED_LAWS.md gives a linear form (N = 42.2 + 3.32 × CR) together with an estimator CR ≈ 4.0 × (Brain/Body)^0.25. Neither survives contact with the paper's headline result: the linear form is bounded near 56 across the entire primate CR range and cannot produce 150 at any input, and the estimator returns 1.54 for a human where Dunbar measured 4.1. The assay in lifeHistory.test.ts is what caught it. We implement the log-linear regression and take CR directly, because there is no defensible way to get it from body mass alone.

Relevant once companionship exists: how many others a creature can hold relationships with is a consequence of its brain, not a UI limit.

Parameters

neocortexRatio

number

Returns

number