Encephalisation quotient

Encephalisation quotient is an empirical measure often used as a proxy for the relative intelligence of a certain species. It refers to the difference between the observed brain mass in a species and the brain mass extrapolated from an allometric relationship between brain mass and body mass across species, given the body mass of the target species. If correct, this should give an empirical ranking of organisms from 'dumbest' to 'smartest'. Since this type of ranking places humans unambigiously at the top in terms of braininess, it is considered to be a somewhat accurate measure. It also correlates well in other animal families as to who constitutes the smartest within its family, though comparisons across orders are generally less informative. Humans are unique in having both the highest encephalisation quotient within the mammals and primates, but also the highest encephalisation quotient of all living organisms, while for example octopuses are only the 'smartest' within their respective family.