The Mitochondrial Free Radical Theory of Aging - Supernova: Pliki

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The Mitochondrial Free Radical Theory of Aging
The demographer may retort, in turn, that even very great medical advances will have
only a small impact on maximum life span. The basis for such a belief is that, as simple
mathematics easily reveals, the only way that we can substantially increase maximum lifespan
is by increasing the MRDT. If the MRDT remains at around eight years, then a halving of
overall mortality rates (that is, achievement of a situation in which people survive half of
the diseases, accidents etc. of which they die today) would shift the graph of mortality to the
right by only one MRDT—eight years. But, again, this logic rests on extrapolation: in this
case, on the assertion that the MRDT will be as impervious to future medical advances as it
has been to past ones. The mutually synergistic interactions between various degradative
processes, described in Chapters 5 and 7, suggest exactly the reverse—that substantial
retardation of any one of them, but particularly of mtDNA decline, would indeed stretch
the MRDT.
17.2. Accidents, Diseases and Lifestyle
Another reason why a great increase in lifespan may arrive sooner than is usually
supposed is that people may hasten it by caution in everyday life. A number of studies have
calculated a supposed upper bound on average human lifespan, by analysing how many
people die of accidents and avoidable diseases and how many of “old age” (variously defined)
and calculating an average lifespan if all death from the latter were removed. 4 I have never
seen, however, a calculation of that sort which takes into account the prospect of changes in
lifestyle that people might be expected to undertake in order to reduce their chances of
dying of causes other than old age. It seems highly probable to me that a 50-year-old man
(who wanted to live a long time) considering a parachute jump would be more circumspect
about it if he were risking indefinitely many years of life than if, as now, he were only risking
30 or so. Activities that endanger the lives of others, such as driving, might very easily be
outlawed. Once we begin to incorporate such factors, the numbers that come out of these
calculations may be remarkably different.
17.3. An Operational Definition of the “Defeat” of Aging
“Immortality” is a word so indescribably loaded with implications having nothing to
do with my message that its use in this sentence is the only one you will find in this book. It
is nevertheless necessary to consider, for sociological reasons if no others, where the practical
boundary comes between increased lifespan and indefinite lifespan. It has been said that an
indefinite lifespan is a theoretical impossibility, because there will always be some biological
process, however slow, that will catch up with us in the end. This is logically incorrect, because
“all” that is in fact needed is a steady stream of medical advances which, cumulatively, increases
lifespan (for people of all ages) by a rate faster than the passage of time. If one doubts the
plausibility that such a stream will happen, once begun, one should reflect that our
understanding of the human body is rapidly—and not asymptotically—improving while
the body itself is not getting more complex.
I believe that in practice, therefore, what matters most from a sociological point of
view is not whether (or when) large numbers of people are actually living much longer than
now but when such a thing becomes perceived to be attainable. This perception will not
necessarily even await the advent of effective human life-extension therapy. A single
well-documented case of a treatment that doubled the longevity of mice, and which most
specialists declare likely to work comparably well in humans too (as would probably be the
case for both the approaches discussed here, in Chapters 14 and 15) would be quite sufficient,
I believe, to trigger a drastic alteration of the public mood with regard to all life-threatening
aspects of everyday life. This alteration would be hardly less great than if the announcement