10.5 老年生物学的未来

We have presented both the optimistic and the pessimistic views on what individuals might encounter in a society where the average healthy life span extends beyond the century mark. The optimists tend to see a society of great opportunity, where the more distant reality of death allows significantly more freedom to explore new possibilities without urgency and the constraints of time. Greater exploration and experimentation in the arts, sciences, medicine, and other fields will ultimately lead to an expansion of human knowledge, thereby accelerating human progress. All of humanity will benefit. The pessimists suggest that a sense of urgency arising from a not-so-distant end of life is a powerful force through which individuals feel the need to put their heart and soul into their work or ambition. It is this sense of urgency that underlies the progress of a society. A long life may remove that urgency and lead to less rather than more progress.

No one can say with certainty what society will become. Of course, that was not our point here. Rather, our hope is that you will have gained a greater appreciation for points of view that you may not have expected or experienced. Most of us may never have given thought to the idea that reducing or even halting research on how to retard aging and increase longevity might be an acceptable alternative to the current push for slowing the rate of human aging. If we accept that the pessimistic view has validity—and we suggest that it does—then we must consider how valuable research on aging retardation is to society. Placing the research emphasis on curing disease and compressing morbidity within the life span we already have might be more valuable to humanity.

The reality is, however, that research into the slowing of aging will increase rather than decrease in importance. Suffering the maladies of disease and old age will remain repugnant to most humans, even if methods are discovered to compress this morbidity into just a few months. The average life span of humans will continue to increase, and the health of the older population will improve. The resulting increase in life span and health will bring new and difficult challenges for our society. Any adverse effect on the individual can be kept at a minimum and be significantly less dramatic if we keep this discussion alive and allow room for all opinions. The science of biogerontology has a major role to play in this discussion.

ESSENTIAL CONCEPTS

• Aging cannot be modulated, because the laws of thermodynamics are universal and cannot be modified.
• Although aging cannot be modulated, the rate of aging can. To modulate the rate of aging, biogerontologists must begin to ask “Why do we live?” rather than “Why do we die?”
• A genomics approach is required to determine which genes are most susceptible to the second law of thermodynamics.
• Calorie restriction without malnutrition extends mean and maximum life span in every non-genetically modified species tested.
• Altering the macronutrient composition of the diet or increasing its vitamin and mineral content has little effect on life span in calorie-restricted animals.
• Biogerontologists are using simple organisms such as yeast, worms, and flies to investigate the mechanisms underlying life extension through calorie restriction.
• Preliminary results suggest that rhesus macaques that are calorie-restricted to 30% of ad libitum intake seem to have a mean life span slightly greater than that of monkeys fed ad libitum; maximum life span may not be different. Potential differences are small compared with those observed in other species.
• Calorie-restricted monkeys have lower rates of age-related diseases than ad libitum-fed animals.
• The effectiveness of calorie restriction in humans remains unknown and controversial.
• The lower risk of age-related disease achieved through physical activity has the potential to increase mean life span; exercise does not increase maximum life span.
• The primary effect of physical activity in slowing the rate of aging is to increase reserve capacity.
• The aging population of the future will be characterized by extended youth and the compression of morbidity.
• Extended youth and compression of morbidity will challenge our concepts of personal achievement, the importance of renewal of the species, and the generational structure of the family and society.

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