Every step forward in understanding human mortality brings with it new questions. Over the past quarter century, a heated debate has divided the scientific community between who sees immortality on the horizon and who instead identifies precise biological limits to lifespan. Who is right? And how could research in this field continue?
The Truth About Human Mortality
Increasing life expectancy has been one of humanity's greatest recent successes. Advances in public health that began in the 19th century kick-started this remarkable process, while recent advances have been achieved by reducing mortality rates in adulthood and old age.
However, in the last 30 years reality is showing some possible limits. As they point out S. Jay Olshansky e Bruce A. Carnes in this interesting study, researchers of the The Journals of Gerontology, there are biological barriers that cannot be ignored, no matter how much mathematics might suggest otherwise.
Human mortality follows regular and predictable patterns, so much so that in 1825 Benjamin Gompertz coined the term “law of mortality” to describe it. And this law, they say, has precise boundaries.
The Mathematical Limits of Human Mortality
One school of thought, based purely on mathematics, suggests that mortality rates could continue to decline indefinitely, theoretically reaching zero: that is, immortality. This view is based on the assumption that medical technology can always “manufacture” more lifespan. Among its exponents is Aubrey De Grey, a researcher in the field of longevity, who he has written a lot in recent years.
This line of reasoning is reminiscent of Zeno's paradox, formulated in 450 BC, according to which an arrow would never reach its target because the distance can be mathematically halved to infinity. In physical reality, however, the arrow always hits the target.
The same is true of human mortality: Mathematical models that predict immortality, say Olshansky and Carnes, do not take into account the limits imposed by the biology of the human body.
The evidence of sports records
An illuminating example comes from the world of sport. The world record for the 1500 metres has improved linearly since 1912, when Abel Kiviat he ran it in 3 minutes and 55 seconds, up to the current record of Hicham El Guerrouj of 3 minutes and 26 seconds achieved in 1998.
Following the same kind of mathematical projection used for longevity, in some centuries the 1500 meters will perhaps be covered instantaneously? An obvious absurdity that shows the limits of this purely mathematical approach.
Biological barriers
Just as there are no specific biological constraints on running speed, but the design of the human body imposes indirect limits, the same is true for longevity and thus human mortality. Humans They cannot run as fast as a cheetah or live as long as a Greenland shark (392 ± 120 years) because our body design evolved with other priorities.
Human longevity is an indirect byproduct of fixed genetic programs that optimize growth, development, and reproduction. Aging is the unintended consequence of accumulated damage to the same biological mechanisms that keep us alive. How do we balance this dynamic?
The phenomenon of entropy
More than a quarter of a century ago, Olshansky and colleagues have demonstrated a phenomenon called “life-table entropy”: the higher life expectancy increases, the more difficult it becomes to increase it further.
When life expectancy at birth is approaching 80 years old, the vast majority of deaths It is concentrated between 60 and 95 years of age. Mortality rates in this age group are very high, with a doubling time of approximately 7-8 years, mainly because aging becomes the dominant risk factor for disease. Perhaps, then, we must “simply” aim for a different strategy than that of seeking an “elixir of long life”.
Human Longevity and Mortality: Towards a New Paradigm?
The solution, of course, is not to abandon efforts to save lives in old age, but to recognize that life expectancy becomes less sensitive to declines in mortality after age 80. Treatments for major killer diseases will therefore no longer produce large increases in life expectancy.
The important directions for the future then become two. One is to strengthen the systems to repair and/or replace the "parts" of us that do not work. Genetics, transplants and other remedies. The other, however, is not so much to prolong life at all costs as to extend the period of life in good health. As highlighted by Gerontological Society of America, the focus of research should shift towards what is called “morbidity compression” (i.e. reducing as much as possible the period of life spent in poor health).
The future of research
Regardless of existing studies and current estimates by researchers, I don't think anyone can predict with any certainty how advances in the biology of aging will affect future life expectancy. What we do know, however, is that focusing on extending the span of healthy life, rather than on prolonging life itself, is a more realistic and valuable goal.
Questions about the upper limits of life expectancy should be left to the esoteric elements of mathematical demography, or perhaps to science fiction. The real challenge for modern science is to improve the quality of life in the years we have, not necessarily to chase immortality, although I would turn the question around: are we sure that this is really a mirage?
