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The Dragons of Eden: Speculations on the Evolution of Human Intelligence is a Pulitzer prize[1] 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 main issues featured in the book is the search for a quantitative way of measuring intelligence. Sagan shows that the brain to body mass ratio is an extremely good indicator, with humans having the highest and dolphins second (pp.38–40, hardback ed.). It does break down, however, at the extremely small end of the scale. Because a certain minimum size is needed to sustain life[citation needed], smaller creatures (ants in particular) place disproportionally high on the list.

Other topics mentioned include the evolution of the brain (with emphasis on the function of the neocortex in humans), the evolutionary purpose of sleep and dreams, demonstration of sign language abilities by chimps and the purpose of mankind's innate fears and myths. The title "The Dragons of Eden" refers to man's early struggle for survival in the face of predators, and how fear of reptiles may have led to cultural beliefs and myths about dragons and snakes.

Opening Quote[]

Mankind is poised midway between the gods and the beasts. - Plotinus


  • Introduction
  • The Cosmic Calendar
  • Genes and Brains
  • The Brain and the Chariot
  • Eden as a Metaphor: The Evolution of Man
  • The Abstractions of Beasts
  • Tales of Dim Eden
  • Lovers and Madmen
  • The Future Evolution of the Brain
  • Knowledge is Our Destiny:Terrestrial and Extraterrestrial Intelligence

Summary of the Chapters[]

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.. are a consequence of its anatomy and physiology and nothing more"—in reference to the great works of Charles Darwin and Alfred Russel Wallace.

In chapter 2, he briefly summarizes the entire evolution of species starting from the Big Bang to the beginning of the human civilization with the help of a "Cosmic Calendar", where every billion years of life corresponds to about twenty-four days of the calendar.

It is disconcerting to find that in such a cosmic year the Earth does not condense out of interstellar matter until early September, dinosaurs emerge on Christmas Eve; flowers arise on December 28th; and men and women originate at 10:30 P.M on New Year's Eve. All of recorded history occupies the last ten seconds of December 31; and the time from the waning of the Middle Ages to the present occupies little more than one second.