He argues that the brain to body mass ratio is an extremely good correlative indicator for intelligence, with humans having the highest ratio and dolphins the second highest,[1] though he views the trend as breaking down at smaller scales, with some small animals (ants in particular) placing disproportionately high on the list.

[3] The book is an expansion of the Jacob Bronowski Memorial Lecture in Natural Philosophy which Sagan gave at the University of Toronto.

In the introduction Sagan presents his thesis – that "the mind ... [is] a consequence of its anatomy and physiology and nothing more" – in reference to the works of Charles Darwin and Alfred Russel Wallace.

All of recorded history occupies the last 10 seconds of December 31; and the time from the waning of the Middle Ages to the present occupies little more than one second.Writing for the New York Times, John Leonard called the book "a delight" and described Sagan as "a scientific Robert Redford, handsome and articulate and all business."

[4] In 2008, an album called The Dragons of Eden was released by keyboard player and producer Travis Dickerson along with guitar virtuoso Buckethead and drummer Bryan "Brain" Mantia.