With this book, Hayflick, a professor of biology (Univ. of California Medical School) who specializes in the study of aging, makes a valiant -- and largely successful -- attempt to summarize for lay readers the current research and theories in his field. Old age, as Hayrick points out, is in its infancy: Only during this century, and only in industrialized nations, have people lived long enough to grow old in large numbers. Hayflick lays out most of what is known about what happens as people age and outlines many of the theories and studies that try to explain the process. Along the way, he touches on ethical questions raised by the possibility of prolonging life and debunks the quackery that has pushed grafted monkey testicles, goat gland transplants, dried fetal cell injections, and other absurd remedies as anti-aging treatments. He also passes along such intriguing tidbits as the fact that normal cells can subdivide only 40 to 50 times before dying, but cancer cells are ""immortal"" and can replicate themselves indefinitely; that neither exercise nor antioxidants have been shown to slow the aging process; and that people who are up to 20% heavier than the ""ideal"" weight set by insurance company charts live longer than those who are underweight. Hayflick covers too much ground to linger on any one point, and that can be frustrating. He repeatedly cites the age of 115, for instance, as the maximum possible life span yet neglects to explain how he can be so sure. Despite its entertaining aphorisms and witty asides, this book is probably too dense to gain the audience its subject matter deserves. But for readers with a high tolerance for polysyllabic words and more than a passing interest in the biology of aging, it's an informative and often entertaining overview.