Brain weight-body weight scaling in breeds of dogs and cats.

Autopsy data from 2,100 pet dogs are used to demonstrate that mean brain weight (y) in 26 breeds of dogs is related to mean body weight (x) by the function y = 0.39 x 0.27. Power functions with the exponent 0.27 appear to define intra-species brain-body weight scaling in several other species. These functions may serve as base lines for measuring increases or decreases in encephalization during species evolution. Curiously, averaged data from 1,250 domestic cats of 2 breeds can be plotted on a line with slope of 0.67, which is known to define inter- rather than intra-species brain-body weight scaling among mammals.