THE CLOCK OF AGES

Aging is a universal human experience, yet even now a poorly understood one; Medina's book is an accessible summary of what we know. Medina (Bioengineering/Univ. of Washington) begins with a brief description of his own mother's life and last days, which inspired him to investigate the aging process. The text then turns to a discussion of the biological meaning of aging and death. A key point is that death is not the simultaneous failure of an entire organism; it is the failure of some key component, such as the heart or lungs, that brings about the end. Medina thus devotes the middle portion of the book to an examination of how each system of the body changes with age. The skin wrinkles, the bones weaken, the lungs lose their capacity to oxygenate blood. But the processes do not proceed at the same pace; half the nerve cells in the occipital cortex will die before a human reaches old age, but almost all those in the thalamus will survive. Vision and hearing deteriorate, but taste buds actually regenerate. Each chapter is introduced with a brief biography of a person whose death in some way illuminates the system under discussion and adds human interest: Goya for the brain, Elizabeth Barrett Browning for the heart, Casanova for the reproductive system. Finally, Medina looks at aging from the biochemical perspective. One theory suggests that aging is a result of cumulative errors in the reproduction of an organism's cells; another, that it is programmed into the genes and promoted by toxic waste products of metabolism. (There is good evidence for both.) Finally, strategies to combat aging are discussed: exercise, a moderated diet, the replacement of certain hormones that decrease with age. While no one has discovered a way to prevent aging and death, Medina ably brings together what we know about these inevitable processes and provides insight into possible avenues of future research.