A remarkably candid book on what we know and (mostly) what we don't know about evolution and extinction. Raup, a ``statistical'' paleontologist at the Univ. of Chicago, is best known for his popular exposition of a theory that extinctions come in 25-million- year cycles, an idea that spawned the notion that the sun had a dark companion (``Nemesis'') that periodically triggered cometary showers that wrecked havoc on earth. Maybe not Nemesis, Raup says, but he still holds out for periodicity and mass killing via meteor impact. Before reviewing theories of extinction, Raup provides useful insights and details on evolution and a number of tables illustrating time scales, percentages of organisms dying, etc., as well as a philosophical discussion of the value of extinction. He argues that an extinction-free world might not lead to as much diversity as the world has enjoyed. We can't be sure, but would birds or whales or humans have evolved in the absence of the terrain created after mass killings of other species? Everywhere, he urges caution--the data are not available; people are distressingly anthropomorphic as well as suspicious of unearthly theories of extinction. In a wonderful tour de force, he lays out the arguments and counterarguments for the theory that large impact craters are the cause for mass extinctions. Both sides are convincing. In the end, Raup makes a strong case that extinction is necessary for evolution and largely blind to the fitness of organisms. A first strike, such as human intervention or an epidemic disease, may trigger the beginning of extinction. So may bad genes. But, overall, bad luck is more likely. While the book is important for what it has to say about life on earth, it is also a marvelous exposition of think and double-think in science.