Figure 1.

Total blood flow rate of both ICAs $({\dot{Q}}_{\mathrm{ICA}}),$ calculated from ICA foramen radius data with the new, ‘empirical equation’ and a wall thickness-to-lumen radius ratio of w = 0.30, in relation to brain volume (V_br) in selected hominids. Means, 95% CI and sample sizes are shown. Inset is the regression of log₁₀ ${\dot{Q}}_{\mathrm{ICA}}$ against log₁₀ V_br for four genera of hominids, namely Pongo, Pan, Gorilla and archaic H. sapiens (unfilled circles), showing that Australopithecus (filled circle) falls well below the regression mean's 95% confidence bands (dashed lines) and 95% prediction limits (thin red lines). See electronic supplementary material, table S2 for statistics of individual species. (Online version in colour.)