average genotype, extremely long life spans are genetically determined. Of course, studying humans to uncover the genetics of aging is not ideal, not so much because one cannot easily perform experiments as because they live such a long time. This is why most of this book describes the current state of research with model organisms such as yeast, worms, flies, and mice. J aswinski focuses on yeast and how metabolic activity and stress resistance affect the longevity of Saccharomyces cerevisiae. In the process, he discusses the concept of aging as applied to a unicellular organism such as yeast and the importance of metabolism and stress resistance for aging in all organisms.