The Dragons of Eden, Speculations on the Evolution of Human Intelligence is a Pulitzer prize winning 1977 book by Carl Sagan. In it, he combines the fields of anthropology, evolutionary biology, psychology, and computer science to give a well balanced perspective of how human intelligence evolved.
One of the more interesting parts of the book is the search for a quantitative way of measuring intelligence. He shows that the ratio of brainmass/bodymass is an extremely good indicator, with humans having the highest and dolphins second (Pages 38-40, Hardback edition). It does break down, however, at the extreme small end of the scale. Because a certain minimum size is needed to sustain life, smaller creatures (ants in particular) place disproportionally high on the list.
By a "good indicator" of intelligence, we mean one that confirms our preconceived notion that humans are the most intelligent organisms on earth.
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