Ward demonstrates that the old adage ""those who don't remember the past are condemned to repeat it"" applies to natural history as well as human history. Ward, a paleontologist, eloquently argues this case in a whirlwind tour of the history of life on Earth. The number of species has gradually increased over the past 570 million years, but this trend has been periodically interrupted by 15 documented mass extinctions. Those that occurred 245 million and 65 million years ago particularly stand out. These events wiped out over one-half of the world's plant and animal species while completely reorganizing the planet's ecosystems. The first extinction paved the way for the dinosaurs. The second eliminated the dinosaurs and enabled mammals to dominate the land. Ward thinks we are in the midst of a third calamitous mass extinction that began 2.5 million year ago with the onset of the first Ice Age. The current mass extinction, like the first two, is accompanied by a drop in sea level and a gradual change in global temperature. Whereas a meteor impact delivered the dinosaurs' coup de grÃ¢ce, the current extinction is being exacerbated by humanity's disturbance of fragile ecosystems. Ward cites the disappearance of species in Hawaii and North America to illustrate this chain of events. But whereas those extinctions were largely caused by preindustrial peoples, Ward notes that overpopulation, global warming, deforestation, and ozone depletion will accelerate the process. By examining biodiversity from a historical perspective, this book complements Harvard biologist Edward O. Wilson's The Diversity of Life. Most readers inclined to purchase this book will likely share Ward's impassioned concern regarding the great catastrophe now underway. Perhaps the book's only major deficiency is Ward's failure to explain to the Rush Limbaughs of the world why we should care if humankind continues to decimate the Earth's flora and fauna.