The Dragons of Eden: Speculations on the Evolution of Human Intelligence

by Carl Sagan

Random House, $8.95

What happens when an astronomer and space scientist turns inward to an exploration of the human brain? If the man is Carl Sagan, he writes a rational, elegant, and witty book about how the brain has come to function, and about our presumption that “mankind is poised between the gods and the beasts.” For Sagan, who teaches at Cornell, the universe is so concinnate that he has neither need nor patience for the current addiction to astrology, Scientology, transplanted Oriental mysticisms, and assorted quackeries as aids to a better understanding of man’s place in it.

One of the particular values of The Dragons of Eden is Sagan’s insistence that the reader do some hard thinking. The second chapter is, as he acknowledges, difficult for even an initiated layman—reading it is akin to climbing the Matterhorn without crampons or ice ax. One must pay attention at every crack and cranny. After that, the going is illuminating and frequently delightful.

Sagan is principally preoccupied with the neocortex, with its left hemisphere, responsible for language and logic, a right hemisphere in charge of intuition and spatial dimension, and a corpus callosum that mediates and synthesizes the two. The book offers many diversions along the way—an examination of myths, of dreams and dreaming, of left-handedness versus righthandedness, of the moment when abortion crosses the boundary that divides the possibly humane from the possibly criminal, of the teaching of chimpanzees to communicate. He writes of the future of computers and the likelihood that someday science will find it possible to apply by computer technology “eyeglasses to the mind.”

No doubt some scientists will quarrel or quibble over some of Sagan’s speculations. Many others will surely squirm with envy that one of their number can combine such clarity and charm of prose with a considerable measure of humility.