Did you notice the picture of the magnificent redwood trees on this page? One coastal redwood, General Sherman, is over three thousand years old. Remarkably the history of this tree has spanned most of recorded human history. One hundred and twenty human generations have come and gone during the life of this 'wonder' of longevity. We have all reflected, I think, at some time or another on the life span of other species. Sadly, we know that our beloved pooch will not live beyond twenty years and that cats, even with nine lives, will not make it past their 30th birthday. However, species like marine bivalves can live up to 220 years. The great ocean tortoises, seemingly as vigorous at 150 years of age as tortoises that are one hundred years younger, bring new meaning to the expression "one hundred years young".
Longevity has always fascinated mankind. We hear distant and remote echoes of this fascination through the earliest known Hebrew and Greek texts. These texts are replete with stories and tales of long-surviving individuals. For centuries, even well recognized authorities believed these claims of longevity. In the 1800s, however, the French naturalist Georges Buffon "recognize(d) that humans, regardless of their race or social station, rarely lived beyond a hundred years." Later, the British demographer, William Thomas, in his classic 1873 study, expanded upon Buffon's insight by "proving" through a comprehensive examination of insurance company records that "Buffon's upper limit of one hundred years was substantially correct."
What determines that boundary, the upper limit of human life span? William R. Clark, Author of the book A Means to an End; The Biological Basis of Aging and Death, states that consistency of life span across generations and species "can be taken as a priori evidence that [it] is at least in part a genetically determined trait." A gene for longevity has yet to be found. However, it is interesting that, despite numerous studies, very few attributes have been shown to correlate with life span. Metabolic rate is one; slowing metabolism via caloric restriction doubles the life span in some species (see "Eat Less and Drink from the Fountain of Youth", Geriatrics & Aging, June 2000). Gender is another; on average, women live seven years longer than men. This difference in life span between the two genders is a well-known fact, which is often attributed to the higher mortality of males in childhood and middle age. What is not so well known is that female centenarians live consistently longer than male centenarians. The evidence seems to support a genetic factor as a preponderant contributor to longevity. Another important observation, and this may be the very reason why some species are programmed to live longer than others, is that life span directly correlates with the time needed for reproduction and the rearing of offspring.
If life span is under strict genetic control, current research suggests that it may be possible to manipulate the genes governing aging. This area of research is advancing rapidly and the amount of information on age-related gene expression is increasing exponentially (see "Dance of A few Genes", Geriatrics & Aging, June 2000). Tomas Prolla, in an interview published in our June issue, opined that his experiments on skeletal muscle have yielded more information on "aging gene expression than all other previous experiments combined". It is already clear that in the next five years we will learn more about both tissue-specific and systemic aging than has been learned in the last two thousand years of thinking, brooding and inquiring into the mysteries of this process.
If the life span could indeed be increased--and this may not be a utopian dream if the current research actually bears fruit--the implications for our society would be epochal.
Clearly the vast store of human experience and knowledge, which is lost because of early death, could be directed at refashioning the world. The additional years of productive and healthy life would unleash untold and unparalleled amounts of creativity and human potential. On the other hand, this would create an array of challenges to overcome--from the re-organization of our society to accommodate the changing demographics, to the restructuring of some of our basic institutions in order to accommodate different societal priorities and goals.
The social, medical, economic and ethical implications of a lengthier human life span are so complex and daunting that the subject has been shunned as a topic of serious discussion. Developments that are underway in research laboratories around the world make the subject and the topic, however, a matter of special urgency and significance. We intend to make Geriatrics & Aging a forum for discussions on this topic. In 2001, we plan to convene a round-table discussion on aging, with leading authorities in the field, in order to examine in-depth what these implications might be. We invite our readers to participate in this discussion by e-mail and we are also exploring the idea of broadcasting this session over the Internet.
I would appreciate your thoughts and feedback on this subject and your interest in the roundtable discussion. Please e-mail any suggestions or comments to geriatrics@ribosome.com.
