The subtitle of [Broca's Brain], "Reflections on the Romance of Science," encapsulates its blend of accepted fact with personal conjecture. In Sagan's world the romance is not monogamous; it is a flirtation with virtually every branch of thought and study. Science qua science lies at its heart, but other relationships provide zest and perspective. In the introduction, Sagan warns that, as is his wont, he has not hesitated to interject social, political, or historical remarks. If he had, this might become his last popular book. His core topics—planetary exploration, the quest for extraterrestrial intelligence, cosmic evolution—are intrinsically fascinating, but other writers address them too. Sagan's secret lies not just in subject but in insight and perspicacious linkages.

In these Broca's Brain abounds, but in flow it wants badly. Its five large parts and 25 chapters connect only loosely—hardly surprising given their heterogeneous origins, many having been...