The neurobiologist Harry Jerison has made a long study of the trajectory of brain evolution since the advent of life on dry land.... the origin of new faunal groups is usually accompanied by a jump in the relative size of the brain, known as encephalization.... the first archaic mammals... were equipped with brains four to five times bigger than the average reptilian brain... primates are twice as encephalized as the average mammal. Within primates, the apes... are some twice the average size. And humans are three times as encephalized as the average ape.

The Origin of Humankind (1994)