Academic journal article Generations

Troubling Implications of Doubling the Human Lifespan

Academic journal article Generations

Troubling Implications of Doubling the Human Lifespan

Article excerpt

Consequences in every aspect of life.

To live longer with fewer infirmities of old age is a nearly universal human desire. Several recent announcements have revived speculation that a significantly longer lifespan may finally be within reach. The demand for the technology that could accomplish this lengthening would be unprecedented-so also the problems it would create. Here, after a brief look at the reasons that lifespan extension may well be near, is an attempt to sketch in broad strokes some of the social displacement it might create.

INCREASING THE MAXIMUM LIFESPAN

Of course the average length of life, or life expectancy, has increased steadily over the past two centuries in Europe and North America, largely because of improvements in living standards, nutrition, and public health. Nevertheless, the maximum lifespan has remained fairly constant. With rare exceptions, the longest humans can live is about iio years. Most animals face a similar limit, though it varies widely from species to species.

Caloric reduction. The maximum lifespan of laboratory animals is currently being expanded by a number of methods. An established and widely reproduced technique is reduction of the number of calories the animals are fed by about 40 percent. Lifespans have been lengthened by 30 percent to 50 percent or more in several species of short-lived animals such as fruit flies and nematodes (worms). Experiments with longer-lived primates are yielding preliminary results that suggest a similar effect. Experiments with humans have been considered, though it is difficult to imagine the general population practicing severe dietary restrictions over an entire lifetime.

Genetic manipulation. The diet itself may be unnecessary, however, if the effects of caloric restriction can be produced by genetic manipulation. A large step in this direction was announced in December of 2000 in the journal Science. Under the direction of Stephen L. Helfand of the University of Connecticut Health Center in Farmington, researchers accidentally disabled a gene that they then learned directs cells to make a protein that helps move nutrients across the cell membrane. The average lifespans of the fruit flies with the altered gene, which the researchers dubbed "indy;" for I'm Not Dead Yet, almost doubled, from 37 to 71 days, and the maximum span increased from 70 to iio days. It appears that they "inadvertently created the effect of caloric restriction genetically;' Helfand said in The New York Times (Kolata, 2000). If this proves to be correct, he added, a drug could be produced that would retard aging without the necessity of a restricted diet. The fact that only a single gene is involved is especially exciting Steven Austad of the University of Iowa told the reporter, since "it gives us something quite specific that we can look at quite easily."

Doubling the lifespan. Impressive results are being produced in several other laboratories using different methods. Thomas Johnson at the University of Colorado has produced strains of the transparent roundworm C elegans that live twice the normal lifespan. At McGill University, in the lab of Siegfried Hekemi, roundworms have been produced that live five times the normal lifespan. To translate that into human terms, it would be comparable to a human lifespan of 400 to 500 years (McDonald, 1997). Of course, the possibility of transferring such results to humans is uncertain and attempts to do so would raise complex ethical issues of experimentation with human subjects. Nevertheless, several leading researchers believe that we will eventually be able to double the human lifespan. This figure, though certainly speculative, appears to be the one most commonly accepted as possible within a few generations and is the one we will assume for the present discussion.

Slowing aging. For simplicity of illustration, we are assuming the longevity intervention to be a form of germ-line enhancement or at least an intervention delivered early in life. …

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