The Dragons of Eden


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 perspective of how human intelligence evolved.

The opening quote is by Greek philosopher Plotinus: ‘Mankind is poised midway between the Gods and the Beasts.’

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. It does break down, however, at the extremely small end of the scale. 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.

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.

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.

The book recounts a story, probably fictional, about the lack of accuracy in text translation programs. An entourage that included an American Senator was proudly led to a demonstration of a translation program. The Senator suggested a phrase to be translated, ‘Out of sight, out of mind.’ The machine printed Chinese characters and these were then entered into the machine to be translated back to English. The visitors were all astonished when the machine printed the phrase ‘invisible idiot’ on the paper. The computer had literally translated the separate expressions ‘out of sight’ and ‘out of mind.’


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