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Equation 1 · Part 4 · Dunbar's Number: The Limit That Might Not Exist

Symbol V_neocortex

log⁡(Ngroup)=α+β⋅log⁡(VneocortexVrest of brain)\log(N_{\text{group}}) = \alpha + \beta \cdot \log\left(\frac{V_{\text{neocortex}}}{V_{\text{rest of brain}}}\right)
VneocortexV_{\text{neocortex}}

What this part means

VnV_neocortex occurs above the fraction bar. The numerator is divided by the entire denominator below it.

Its job in the formula

VnV_neocortex occurs above the fraction bar. The numerator is divided by the entire denominator below it.

The passage around this formula

The prediction itself has a precise origin and it is much narrower than its reputation. Robin Dunbar’s 1992 paper in the Journal of Human Evolution ran a comparative regression across primate genera and found that group size tracked one variable with real predictive power — the ratio of neocortex volume to the volume of the rest of the brain — while the ecological variables he tested alongside it, tied to diet and ranging behavior, did not [ 1 ] . Stated as a model, the claim was this: log⁡(Ngroup)=α+β⋅log⁡(VneocortexVrest of brain)\log(N_{\text{group}}) = \alpha + \beta \cdot \log\left(\frac{V_{\text{neocortex}}}{V_{\text{rest of brain}}}\right). Group size as a function of relative neocortex volume, nothing else in the model earning its keep. Dunbar’s interpretation was mechanistic rather than merely statistical: neocortical…

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Sources cited in the surrounding passage

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