Versatile though he is, [Sagan] is simply not enough saturated in his subject [in "The Dragons of Eden: Speculations on the Evolution of Human Intelligence"] to speculate; what he can do is summarize and, to a limited degree, correlate the results of scattered and tentative modern research on the human brain. The research, from electroencephalograms of dreamers to endocranial casts of fossil skulls, is in progress, and Mr. Sagan, like the rest of us, must wait for sweeping conclusions. "If this result is confirmed, it would be quite an important finding," he writes in one iffy spot, and, in another, complains, "Very little work has been done in this field to date." He speaks of "many potential near-term developments in brain chemistry which hold great promise both for good and for evil," shamelessly woolgathers about how "one day we will have surgically implanted in our brains small replaceable computer modules or radio terminals which will provide us with a rapid and fluent knowledge of Basque, Urdu, Amharic, Ainu, Albanian, Nu, Hopi, !Kung, or delphinese," and, in another connection, allows, "It does not seem to me that a crisp choice among these four alternatives can be made at the present time, and I suspect that the truth will actually embrace most or all of these possibilities." Well, one begins to wonder, what has emerged lately in the study of human intelligence that justifies the production of this book? The dust jacket shows a pair of semi-shaggy primates sitting at ease in a ferny Eden with what appears to be a pet dimetrodon, a pre-dinosaurian reptile that vanished over a hundred million years before the first primates appeared. The book's title also hints at a thematic center that is reptilian. (pp. 87-8)

It is difficult to discern Mr. Sagan's intellectual contribution to the exposition [of the triune brain], other than poetic chapter titles like "Tales of Dim Eden" and piquant epigraphs like—for the chapter sketching the three divisions of the brain—"When shall we three meet again …? (Wm. Shakespeare, 'Macbeth')." The expository pattern tends to alternate facts experimentally discovered by other scientists with personal extrapolations that seem loose, if not facetious….

Mr. Sagan's speculations, where they are not cheerfully wild, seem tacked on and trivial. (p. 88)

[It] remains to say that there is much fascinating information here, amid the fluff of computer printouts, Escher lithographs, and vacuous editorializing on matters ranging from abortion law to government funding for scientific research. (p. 89)