What"s the big deal about big brains? They"re a costly enhancement, says neurobiologist John Allman in Evolving Brains. "Animals with big brains are rare," he stresses. "If brains enable animals to adapt to changing environments, why is it that so few animals have large brains? The reason is that big brains are very expensive." He examines the whys and wherefores of large-brain evolution, and draws out the connections between large brains and long lives; shows why major evolutionary advances are often made by small predators; makes you appreciate why mammals, burdened by the cost of warm-bloodedness, were unable to unseat the dinosaurs; and more. So, while large brains such as the ones we humans enjoy may give survival advantages to individuals, some species have done (and did) just fine for millions of years with pea brains. Rather than talking only about cells, circuits, neurotransmitters, and genes, or gliding up to the ethereal regions of psychology and philosophy, Allman looks at the whole organism--the "middle-sized, middle-distanced objects," as Willard Van Orman Quine said. Evolving Brains is full of interesting scientific tidbits, only rarely becoming tangled in the thicket of jargon. --Mary Ellen Curtin