I wasted time, and now doth time waste me. —William Shakespeare
It is a fact of life that with the slow progression of time we all lose the health and vigor we enjoyed as children and young adults. Statisticians, in a long version of Shakespeare’s eloquent statement, sum it up by saying our chance of dying on any given day increases the older we get. Biologists call this the aging process or, more specifically, cellular senescence.
Aging is a common phenomenon, but it is not universal. It does not occur among prokaryotes, protozoans, and simple multicellular creatures such as sponges and corals. Indeed, if we think of pro-karyotes or protozoans as being a single lineage, it is a life-form that has been alive for 3 billion years (sponges can, in theory, live a very long time, but because of predation few survive beyond 100 years).
There are those who think a human life span of 85 years is long enough, but compared to 3 billion years it truly is the short end of the stick. There are, to be sure, many animals that have a shorter life span than we do: A horse has an average of 20 years, a dog is lucky to see 15 summers, and the common housefly is born and dead of old age in 30 days. On the other hand, some animals, such as the Galapagos tortoise and the sturgeon, live for more than 200 years.
On a cosmic scale, however, the difference in life span between a housefly and a sturgeon is of no consequence. Moreover, the comparison begs the question of why we age in the first place. After all, we have a reasonably good immune system; we heal well after being hurt; we have a group of enzymes that monitor and repair our DNA; and, as long as we eat well, our cells have plenty of energy to take care of themselves from day to day. Yet, despite all that, we get old with monotonous regularity. There appears to be neither rhyme nor reason to it. Some scientists think aging is due to evolutionary neglect: Natural selection was so busy finding ways to make us successful in the short term that it forgot to cover us in our old age. It is almost as though Mother Nature is saying, "I will do what I can to get you up to your reproductive years, so you can have offspring, but after that you are on your own."
Being on our own has meant that our bodies begin to break down soon after our peak reproductive years have past. The elderly cannot run as far, think as fast, or fight off infectious diseases nearly as well as they did when they were young. Moreover, one’s physical appearance changes dramatically with age: The hair turns gray, muscle mass declines, the ears get bigger, and the skin becomes thin and wrinkled. On a deeper level, men and women approaching their 80s converge on a common phenotype; men become more feminine, and women become more masculine. In men this trend becomes apparent as the shoulders get narrower, the hips broader, the beard thinner, and the voice develops a higher pitch. In women the shoulders become broader, the voice huskier, and hair begins to grow on the chin and upper lip. Gerontologists (scientists who study gerontology, or the mechanisms involved in the aging process), in noting these changes, have pondered one of the most difficult questions pertaining to the aging process: Is aging caused by the degenerative changes in a single organ, which then acts like an aging-clock for the rest of the body, or are all organs breaking down simultaneously?
Answering this question has proven to be extremely difficult. Researchers have studied age-related changes in virtually all tissues, organs, and organ systems of the body (the endocrine system, consisting of many hormone-producing glands, is an example of an organ system). Some evidence suggest that the brain may be an aging-clock that determines the rate at which the whole body ages, but the results of many other studies suggest that the rate at which an animal ages may be the sum of age-related changes occurring simultaneously in all parts of the body.
Consequently, the attempts to understand the aging process, involving such a complex system, have generated a great number of theories but few practical therapies. Traditional therapies are available that treat age-related diseases such as cancer and arthritis, but do not reverse the aging process itself. A common trend in gerontology, particularly since the completion of the human genome project, is to search for genes that have a demonstrable effect on life span, the so-called longevity genes. Many such genes have been identified, and although the manipulation of these genes does not stop the aging process, they are providing many valuable insights into the cellular mechanisms of aging. More recently interest has turned to the use of cloning technology, stem cell analysis, and genetic manipulation in order to produce an effective rejuvenation therapy for cells and the body as a whole.
Aging, Revised Edition, one volume in the multivolume the New Biology set, describes the field of gerontology and the many theories that scientists have developed over the years to explain the age- related changes that occur in nearly all animals. This edition, now with color photographs and line drawings, has been extensively revised and expanded.
Rejuvenation is usually discussed in very general terms, but this topic gives a detailed account of how current technologies could be used to produce an effective rejuvenation therapy. More practical therapies, based on clinical trials.This topic describes some exciting studies that may provide effective treatments for Alzheimer’s disease, cardiovascular disease, and osteoporosis. The final topic, as before, provides background material on cell biology, biotechnology, and other topics that are relevant to gerontology. The cell biology and biotechnology primers presented in this topic have been revised and condensed in the hope that the reader will be able to obtain the necessary background information as quickly as possible.