 Brain size was previously considered a major indicator of the intelligence of an animal . Since most of the brain is used for maintaining bodily functions , greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks . Allometric analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass . Comparison of a particular animal 's brain size with the expected brain size based on such allometric analysis provides an encephalisation quotient that can be used as another indication of animal intelligence . Sperm whales have the largest brain mass of any animal on earth , averaging 8 @,@ 000 cubic centimetres ( 490 in3 ) and 7 @.@ 8 kilograms ( 17 lb ) in mature males , in comparison to the average human brain which averages 1 @,@ 450 cubic centimetres ( 88 in3 ) in mature males . The brain to body mass ratio in some odontocetes , such as belugas and narwhals , is second only to humans . 
