Fascinating theories and cogent insights into why and how we use language, as learned from our simian relatives. Dunbar (The Trouble with Science, not reviewed) is a psychologist at the University of Liverpool, but his lucid Darwinian forays into the evolution of language draw widely on the fields of anatomy, linguistics, sociology, and anthropology. Monkeys spend up to 20 percent of their day grooming, and they are not just nit-picking: The activity allows them to communicate trust, form protective social alliances, and gossip, as it were, to keep track of who's monkeying around with whom. Using adaptation to environment as the evolutionary trigger, Dunbar shows how human language might have evolved to replace grooming when societies got too large to keep up with important information. Such gossip might warn a friend or relative about repeating a mistake or trusting the wrong clan members in a key social activity. And while humans don't depend on their hairdressers for protection from leopards, Dunbar points out that actual grooming and verbal ego-massaging release natural opiates that keep us high. While his primary focus is on humans, Dunbar weaves in a considerable (indeed, slightly excessive) amount of material about the linguistic abilities and social behavior of other species, including the vampire bat, the most loquacious sub-primate. While stressing the complex talents of our fellow primates, he concedes that ``if the apes have some form of science or religion, it cannot be very sophisticated.'' Dunbar concludes with a fascinating meditation on clan loyalty and the development of dialects and a variety of languages. An enjoyable romp through the past few hundred thousand years. Where else could you learn that it takes a village to grow a neocortex or that, to reproduce the best genes, women network and men advertise?