Book excerpt: Extensively revised and updated to reflect the current state of knowledge in the study of aging, this Fourth Edition offers a complete profile of the aging process at all levels, from molecules and cells to demography and evolution. Written by international experts in current basic and clinical aging research, this text includes aspects of individual, comparative, and differential aging, and discussions of theories and mechanisms of aging. This invaluable reference illustrates how bodily systems, organs, and functions are affected with aging, describes how genetic and environmental factors influence age-related changes, and addresses some of the clinical consequences of these changes for health and longevity. Well illustrated, with numerous tables and graphs, this book presents up-to-date information from internationally renowned experts in various bio-medical fields.