Books: Brain Matter

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THE DRAGONS OF EDEN by CARL SAGAN 263 pages. Random House.

Like squids, scientists protect themselves with clouds of impenetrable ink. Not Carl Sagan. His jargon-free book The Cosmic Connection (1973) involved thousands of readers in the search for life beyond earth. Last year, during the Mars probe, he became a TV celebrity with plausible descriptions of the creatures that might be populating outer space. The Dragons of Eden should involve thousands more in the exploration of inner space — the human brain.

Sagan, 42, occupant of a chair in astronomy at Cornell University, is not a neuroscientist. But he writes about the brain with uncommon sense and even humor. With many social critics, he recognizes that human intelligence is the main source of mankind's present crises. With Albert Schweitzer, he believes that "only a worldview which accomplishes all that rationalism did has a right to condemn rationalism."

The Dragons of Eden begins with a summary of how and when intelligence developed in various terrestrial species. In detail, Sagan describes the process of natural selection working toward the emergence of the creature Shakespeare called "the paragon of animals." Sagan also explains differences in the structure of the paragon's brain and those of other animals. He offers some idiosyncratic thoughts on why man's neurological legacy makes him behave the way he does.

The human brain, he points out, evolved from the brain of the reptile, one of whose species the Bible holds responsible for the Fall. According to Sagan, the reptilian brain, which forms the most primitive part of the human brain, still influences man's behavior and may help explain one of his oldest fears — the apparently inherent squeamishness about snakes. "When we feared the dragons," inquires the astronomer, "were we fearing a part of ourselves?"

Sagan also wonders if the human fear of falling is not a memory inherited from our arboreal ancestors, who lived in trees and suffered when they forgot the effects of gravity. He speculates too on the reason for dreams. Many neuroscientists believe that dreaming is less a working out of subconscious desires than the means by which humans "debug" or rewrite the mental programs they have picked up during the day. But if this is so, Sagan wonders, why do infants, who presumably have little or no experience to sort out, seem to dream just as much as their elders?

The author does not supply solutions. But arguing, as always, for life Out There, he believes humans must press for answers. Only by understanding our own minds, he maintains, can we hope to understand the other civilizations we are trying so hard to reach. Intelligent organisms evolving on another world may not resemble man physically or be anything like him biochemically. But they are likely to reason similarly, for whatever their worlds, they are still subject to the same laws of chemistry and physics. "Natural selection," writes Sagan, "has served as a kind of intellectual sieve, producing brains and intelligences increasingly competent to deal with the laws of nature ... the same evolutionary winnowing must have occurred on other worlds that have evolved intelligent beings."