Figure 3

Scaling relationship between the total number of neurons or supporting cells in the brain and brain mass. A Brain mass (in gram) compared with the total number of neurons in the brain for 12 low-level mammal species [47],[62] (solid circle), 11 primates [46],[63] (solid triangle) and 7 ectotherms [44],[48]-[50]. The fit function (in black line) gives W = 0.0052 N^1.12 (adjusted- R² = 0.94, p < 0.01) for the endotherms (where P_endotherm is the brain mass in grams, N is total number of neurons in the brain in millions, and P_ectotherm = 0.0096 N^0.82 (adjusted- R² = 0.65, p < 0.05) for the endotherms. B Brain mass in grams compared with the total number of non-neuron cells in the brain for 12 low-level mammal species [47],[62] (solid circle), 11 primates [46],[63] (solid triangle) and 7 ectotherms [44],[48]-[50]. The fit functions (in black lines) have P_endotherm = 0.0074 N^1.092 (adjusted- R² = 0.993, p < 0.01) for the endotherms (where P_endotherm is brain mass in grams, and N is the total number of non-neuron cells in millions. The datasets for this figure are given in Additional file 4: Table S4.