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Far from being evolutionarily absurd, death is essential if natural selection is to occur. Death is actually fundamental to evolution.
We have to die off in order for another generation with different DNA mix to take our place. That's the point of Natural Selection.
The bottom line here is that if science is to advance our understanding any further, it must reconcile itself with studying a very big part of reality that it now rejects as impossible.
originally posted by: Astyanax
a reply to: swanne
Incorrect. Natural Selection is not dependent on lifespan, it is dependent on the ability to make offsprings with different DNA mix.
Which part of ‘selection’ don’t you understand?
That's true but you can't continue making new generations without the old one's being killed off because the need for space and resources would skyrocket.
originally posted by: swanne
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.
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.
Evolution of ageing
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.
The death rates at extreme old ages start to slow down, which is the opposite of what would be expected if death by aging was programmed. From an individual-selection point of view, having genes that would not result in a programmed death by aging would displace genes that cause programmed death by aging, as individuals would produce more offspring in their longer lifespan and they could increase the survival of their offspring by providing longer parental support.
originally posted by: Barcs
a reply to: swanne
The one issue I see is that aging is mostly irrelevant in the evolutionary picture, especially later in life. Evolution is about passing down genes, not living super long lives. It's not that you "pay the price" later. It's just that evolution can't select for long term anti aging genes because the effects primarily apply to your later life. They may exist, but they are neutral in the evolutionary picture.