The awareness that we are growing old may be uniquely human. Perhaps other animals, particularly some of the higher mammals with rudimentary cognitive function, may be aware that they are slowing down in many ways, unable to keep up with others in their group, less able to find food or capture prey, slower to move away from danger or a predator. But we doubt they understand the full implications of the process. Humans do. Only we wonder how Lachesis measures out her thread; only we want to know the nature of Atropos’ scisssors. Alone among the animal species that inhabit this planet, we are endowed with consciousness, an awareness of self - where we came from, and where we are going. We alone know, only too well, that the endpoint of aging is death. This drives a concern in us about the aging process - senescence - that is completely lacking in other species.

For some, old age is a time of peace and joy, of reflection on life’s bountifulness, a time to contemplate the only immortality we can know - the lives of our children and grandchildren. With luck and a little attention to diet and exercise, we can maintain our ability to engage both physically and mentally in those lives, and in our community of friends. But it is not so for all of us. Genetics, accident, the "luck of the draw" - all of this can play against us in our later years, depriving us of the ability to participate fully and meaningfully in the world around us. All of us have this fear as we sense old age approaching, for it can happen to anyone. And at some level, even in the lucky ones, this fear never really goes away, because we know from observing other lives that at any moment our fate could change.

So it is in a sense fear that drives us to study aging, to try to understand it; to name its parts, to unravel how they work and how it all fits together. Organized attempts to study aging in a systematic way were slow in getting started - the first professional societies dedicated to promoting basic research in senescence and aging (gerontology), and a medical specialty dealing with the problems of the aged (geriatrics), were not formed until the 1940s. As with any new field, the early years of the study of aging were filled with confusion and uncertainty. The aging process seems enormously complicated, involving complex changes in virtually every different cell type in the body. Graying hair, failing eyesight, declining physical ability and mental capacity - each of these seems like a separate physiological process, each with its own biochemical and genetic regulation.

The study of aging has some intriguing similarities to the study of cancer, and these may be instructive. For most of its clinical history, cancer was viewed as a thousand or more different diseases - at least as many different cancers as there were different cell types in the body, each requiring different treatment, each with its own outcome. But today our view of cancer is radically different. What we see now are the incredible similarities of cancer. Nearly all cancers involve mutations in a limited number of genes distributed throughout all cells in the body. This knowledge has provided a completely new basis for designing new strategies for both the detection and the treatment of cancer, strategies that are already finding their way to the clinic. The lesson from cancer that we can apply to aging is the need to understand physiological processes at their most fundamental level - at the level of the very genes that regulate it. Complex organisms like humans are composed of individual cells, and that is where the aging process begins - the aging of any organism is a reflection of the cumulative senescence of its component cells. The enormous variety of cell types in the human body, each with its own peculiar aging characteristics or "phenotype", might seem to confound the search for common cellular aging mechanisms. But just as complexity in cancer came to be viewed as derangements in a limited number of genes operating in all cells, so too may senescence.

These new views of cancer and aging are part of the new field of human medicine called molecular medicine, which is in turn the fruit of basic research throughout this century in biochemistry, genetics and molecular biology. Completion of the Human Genome Project early in the next century will eventually make it possible to identify each of the key genes involved in human aging. We will then be able to dissect senescence and aging at a level never before possible. In the past, we have had to approach aging much as the proverbial blind men approach elephants, describing it from without, in fragmented terms, trying to guess the meaning and origin of each component, with the dimmest of views of the larger picture.

But that is about to change; soon we will see the thread of our lives - once thought to be spun, woven and cut by fate - from a new perspective; from the inside of our own DNA. The guesswork will be gone; the view will be spectacular. What will we do with this information? How will we use it? All of us need to be engaged in a discussion of this and every other aspect of molecular medicine as we enter the next century - the next millennium. Aging is a wonderful place to start. In this book we will take a close look at what molecular medicine and its underlying sciences have to tell us about this most mysterious and fascinating of human biological processes.