Most people think of natural death (death by old age) as being fundamentally caused by the wearing out of the organism. After all, we all get some
form of damage as we grow older, may it be at the molecular level with free radicals or on a more general scale as our body grows weaker. Disorder
steps in with time, and things stop working as they should.
Evolution of ageing
But this idea was discredited in the 19th century when the second law of thermodynamics was formalized. Entropy (disorder) must increase
inevitably within a closed system, but living beings are not closed systems. It is a defining feature of life that it takes in free energy from the
environment and unloads its entropy as waste. Living systems can even build themselves up from seed, and routinely repair themselves. There is no
thermodynamic necessity for senescence.
This is a very good point. The article goes on:
In addition, generic damage or "wear and tear" theories could not explain why biologically similar organisms (e.g. mammals) exhibited such
dramatically different lifespans. Furthermore, this initial theory failed to explain why most organisms maintain themselves so efficiently until
adulthood and then, after reproductive maturity, begin to succumb to age-related damage.
A possible answer is that living beings in nature are often killed (either by accident or by another living being) before they do get the chance to
grow old. Since old age isn't an issue, nature neglects to develop strategies against old age, since most living beings don't get there in the first
place. This is called the "Selection Shadow" argument.
But I have a problem with such an argument: many animals do reach old age. Predators on top of their food chain have but slim chances of being killed
by small preys, and resistance to senescence would in their case actually assure that they stay fit and keep being on the top of their food chain.
So perhaps gene mutations accumulation is to blame? As pointed out by Medawar's Theory, surely mutations accumulate with time, and ultimately causes
general breakdown of the organism?
Modern genetics science has disclosed a possible problem with the mutation accumulation concept in that it is now known that genes are typically
expressed in specific tissues at specific times (see regulation of gene expression). Expression is controlled by some genetic "program" that activates
different genes at different times in the normal growth, development, and day-to-day life of the organism. Defects in genes cause problems (genetic
diseases) when they are not properly expressed when required. A problem late in life suggests that the genetic program called for expression of a gene
only in late life and the mutational defect prevented proper expression. This implies existence of a program that called for different gene expression
at that point in life.
So the mystery still stands.
George C. Williams proposed that Death is in itself the price to pay for beneficial genes.
In antagonistic pleiotropy, one of these effects is beneficial and another is detrimental. In essence, this refers to genes that offer benefits
early in life, but exact a cost later on. If evolution is a race to have the most offspring the fastest, then enhanced early fertility could be
selected even if it came with a price tag that included decline and death later on.
However this theory has been discredited by experiments. Fruit flies that lived twice as long were twice as fertile, directly falsifying Williams'
assumption that fertility and age were mutually exclusive. Also, many ageing genes have no associated benefits, once again proving that there isn't
really a link between the two.
The Disposable Soma Theory proposed that Death was caused by a shortage of Time; since living beings have but limited energy (food) access, then their
organism spends this energy for reproduction instead of long age. But this theory was disproven when it was discovered that many living beings
actually lived longer when they had access to LESS energy (food) than control.
Some theories say that Death is actually programmed as a defence against critical damage, such as cancer. I think this is actually a good point,
however programmed death doesn't solve the crux of the issue: if programmed death is to avoid dying of cancer, then nature still isn't seeking to
prolong life, it's only choosing between death methods. The reason why organisms cannot just live forever is still left unsolved.
But this last theory got me thinking. We already know that cancer is a cell which has been mutated to live and reproduce forever using available
energy all around.
What if Nature IS actually attempting to defeat Death? What if cancer is nature's clumsy, blind shotgun way to try and create organisms that can live
forever - at first succeeding with cells, but then having a bit of some troubles implementing it on a pluricellular level? In which case the answer to
the question, "why doesn't nature work on eliminating natural death" would be, "she's actually working on it. "
Yet another simpler answer is that we simply don't die.
A bit like the Timelords in BBC's Doctor Who
show, it could be that we living beings actually never die, we only change faces. This idea has
roots in the oldest cultures, may it be the reincarnation concept of Hinduism, or the Soul concept of Biblical legends - even animist cultures have
some sort of soul concept. It could be that we have a part of us which lives through the ages, a side of us which dwells in another realm and whose
lifespan only ends once its Universe (the ultimate thermodynamic closed system) reaches total death; and that the only way for this "soul" to interact
with the physical realm is by taking a physical form - living beings. An analogy would be that for you to read this post I have to use a computer and
interact with you via the "realm" we call "Internet". Physical living beings would be only half the equation; they would simply serve as vehicles for
the actual Life - the soul.
In which case the answer to "why do we die? " would simply be, "we don't".
Food for thoughts.
edit on 16-6-2016 by swanne because: (no reason given)