Author and Earth Sciences professor Ward (of the Univ. of Wash.) has authored numerous books for non-specialists (Under a Green Sky, Rare Earth); this latest is a critical response to James Lovelock's Gaia concept, which argues that homeostatic physical and chemical interactions work to maintain Earth's habitability. Ward argues, passionately, that the opposite is true-that living organisms decrease Earth's habitability, hastening its end by perhaps a billion years. His conclusion, more political than scientific, is that humans must engineer the environment to sustain life. Ward provides examples of the food chain in failure, which results in an imbalanced environment and, ultimately, mass extinctions. Unfortunately, Ward's arguments (and some of his facts) are flawed; many examples focus on short periods of time, ignoring ""first causes"" that usually include a natural but temporally and/or geologically distant event (massive volcanic eruptions, ocean impacts, etc.). Moreover, ecological balance was indeed restored over the course of thousands or millions of years, as new organisms evolve to fill the ecological niche left by extinct species. Ward's criticisms have merit, but his Medea hypothesis is only valid on an evolutionarily insignificant scale; the reality is probably some combination of the Gaia and Medea approaches. Unfortunately, Ward doesn't help his case with misanthropic sentiment and occasionally garbled syntax.