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Author Topic:   Is death a product of evolution
platypus
Member (Idle past 3830 days)
Posts: 139
Joined: 11-12-2006


Message 31 of 46 (366982)
11-29-2006 8:37 PM
Reply to: Message 30 by Hawks
11-29-2006 5:31 PM


Re: growing versus spreading
quote:
Anything has a lifespan. Unless there is some input of energy to maintain an equilibrium (e.g. maintain the integrity of DNA) things will tend towards disorder (according to the second law of theromdynamics). I guess you could say that death will result when there is not enough input of energy to maintain the integrity of the metabolic functions in an organism. This could happen when, for instance, not enough food is available or when energy is used to produce offspring instead (See my message #18 for link to an article that talks about the disposable some theory).

There in fact is a constant input of energy, namely sunlight. And some organisms (Homo sapiens, for instance) that live past reproductive age, yet still die. Therefore, neither of these principles can account for death, because the conditions for sustainability are in place. Yet people still die.

I do like the idea of gamete immmortality- does seem to make the distinction between asexuality and sexuality unimportant.


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RAZD
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Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 32 of 46 (366988)
11-29-2006 9:15 PM
Reply to: Message 29 by 2ice_baked_taters
11-28-2006 10:45 PM


Re: growing versus spreading
Perhaps evolution is part of a larger process that includes death. Why lifespans are what they are.

To continue the difference between an individual organism growing and one spreading material to make copy organisms that grow from pieces of the original ...

It could be the point of view.

We see aspen trees covering a mountainside -- all with the same genetics, each "tree" grown from a sap root. Each tree is born, lives and dies, but it is not the organism that is born, lives and dies.

We see fungi grow fruiting bodies that explode and cast spores into the wind. The fruiting body is born, lives, spreads its clones, and dies, but it is not the organism that is born, lives and dies.

We see corals and muscles that cast sexual spores into the water to mix with other sexual spores to make new corals and muscles. The corals and muscles are born, live, spread their seeds, and die, but are they really the organism that is born, lives and dies?

A crab sheds its shell and is it born again? Has the shell cast aside died?

Does a caterpiller die to transform into a butterfly? The body liquifies inside the chrysalis and then reorganises.

Multicellular life is not {created} with new individuals - it has a continuous linear ancestry made by cell division (and sexual combination) from single celled life just as unicellular life has a continuous linear ancestry.

At the cellular level this is no different than a crab changing shells eh?


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2ice_baked_taters
Member (Idle past 3927 days)
Posts: 566
From: Boulder Junction WI.
Joined: 02-16-2006


Message 33 of 46 (366998)
11-29-2006 10:05 PM
Reply to: Message 30 by Hawks
11-29-2006 5:31 PM


Re: growing versus spreading
Anything has a lifespan. Unless there is some input of energy to maintain an equilibrium (e.g. maintain the integrity of DNA) things will tend towards disorder (according to the second law of theromdynamics). I guess you could say that death will result when there is not enough input of energy to maintain the integrity of the metabolic functions in an organism. This could happen when, for instance, not enough food is available or when energy is used to produce offspring instead (See my message #18 for link to an article that talks about the disposable some theory).

DNA/RNA simply replicate themselves correct? How is death a factor here? Multi cellular organisms seek to maintian their reaction. This is not a factor in the case of DNA/RNA. At some point the individual organism began to exist for itself beyond replication. What was the advantage of this and was this when death as we understand it became a factor?

(The following piece will only deal with multucellular organisms)
You asked earlier in message #23 "How does "survival of the fittest" require death?". It doesn't. You can always think of it this way: While "the purpose of a multicellular organism might seem to be to make more multicellular organisms", instead think of it as "the role of gametes (i.e. egg and sperm) is to make more gametes through the vehicle of a multicellular organism". In this sense, multicellular organisms are just as immortal as prokaryotes are (although even they seem to age to an extent).

This is an interesting view. If you are to think in these terms then you should expand this to the entire biomass as a whole. Immortality does not scientifically apply. Neither does implying a specific "purpose" to any multicellular organisms existence. Death is a fact though. Again.....countless living things seek to maintain themselves as individuals far beyond replication. I ask again...the big wind up but how came about the consistent wind down? Was it natures way of balancing an equation?


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RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 34 of 46 (367000)
11-29-2006 10:27 PM
Reply to: Message 33 by 2ice_baked_taters
11-29-2006 10:05 PM


Super organism view
From Message 47

quote:
How, then, is sexual reproduction less costly than asexual propagation?

For the same reason that having specialized organs within an organism is less costly than having all the cells capable of doing all the jobs: specialization and sharing.

Think of a population of a sexual species as a number of super organisms, where individuals are specialized organs within a {population body} -- it is essentially "asexual" in its reproduction of new {population bodies} of the same species, and the {population body} divides when conditions are right, without input from other {species}.

(hmm. this applies to the Thread Is death a product of evolution too ... )


So we can also look at this from a {population body} perspective (as oppossed to the cellular gamete point of view) and see that the {population body} doesn't necessarily die (unless due to significant and persistant natural selection causing extinction of the population), and that individuals are just interchangable parts in the {population body}, like new skin cells.

Edited by RAZD, : linked link later


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Hawks
Member (Idle past 4223 days)
Posts: 41
Joined: 08-20-2006


Message 35 of 46 (367697)
12-04-2006 4:07 PM
Reply to: Message 33 by 2ice_baked_taters
11-29-2006 10:05 PM


Re: growing versus spreading
quote:
DNA/RNA simply replicate themselves correct? How is death a factor here?

Technically speaking, they don't replicate themselves. They code for instructions for how to do it (saying that, some RNAs do have catalytic ability and some are involved in DNA replication - but by themselves they can't do it). This is all very philosophical, but "death" for DNA would be when it is degraded to nucleic acids, I suppose. In any case, I would not say that DNA "dies" with the organism considering that other organisms might still engulf it and potentially incorporate it. On the other hand, it is not really the actual molecules as such that make DNA important, but rather the information they carry. In this sense, DNA would "die" when it no longer carries any meaningful information. This is all just random thoughts, of course...

quote:
Multi cellular organisms seek to maintian their reaction. This is not a factor in the case of DNA/RNA.

It is not the case for proteins or fats either. In fact, you can't point to any singular molecule in an organism and say that is seeks to maintain anything.

quote:
At some point the individual organism began to exist for itself beyond replication. What was the advantage of this and was this when death as we understand it became a factor?

I'm again just being philosophical without presenting any actual data - but that kind of suits the questions anyway, methinks...

I would probably say that death, as I understand you to refer to it (i.e. ageing), would have started whenever organisms became multicellular AND had cells with specialized functions. The question then becomes: why aren't non-reproductive cells immortal so as to allow indefinite reproduction? Well, for starters, there has to be a balance between maintaining the non-reproductive cells versus reproducing. Combine that with the fact that there is a cumulative probability of death (from disasters, predation) one can see why it would be good to have a larger population rather than investing too many resources on growing old when you might die anyway. One can also speculate that perhaps faster reproducing organisms were better at adapting to changing environments, so that longevity is in fact restricted because of competition with members of the same species. So, the answer here as to why we die of age would be that selective forces have come to a balance between the benefits of ageing and reproduction.

To find out the advantage of such a system I suppose one should start looking at organisms that are multicellular but don't have specialised cells (e.g. sponges). Is there, for these organisms, an advantage to live as colonies? Next you can start looking at organism that have just a few specialised cells types and see what kind of advantage this has over organisms such as sponges. I'll leave that as an excercise to those that have the time to look it up (I seem to remember reading about this at some stage, so I THINK that some material might be available).


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RAZD
Member
Posts: 19756
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.5


Message 36 of 46 (367911)
12-06-2006 8:11 AM
Reply to: Message 35 by Hawks
12-04-2006 4:07 PM


death by "old age" is death by one of many means, not just one cause.
I would probably say that death, as I understand you to refer to it (i.e. ageing), would have started whenever organisms became multicellular AND had cells with specialized functions. The question then becomes: why aren't non-reproductive cells immortal so as to allow indefinite reproduction? Well, for starters, there has to be a balance between maintaining the non-reproductive cells versus reproducing.

Let us consider what we mean by death by old age: it is the break-down of one system or another to the point where the organism is no longer viable, able to maintain existence.

This is from a number of very different systems: heart failure is one (although may be linked to viral infections), cancer is another (where control on replacement manufacture of cells goes into overdrive and ends up blocking other systems from operation), brain failure is another (parkinsons, ementia, alzheimers, etc).

What we see is that these systems all seem to fail at about the same age, although different people have different susceptibility to each kind of failure, and some get hit with multiple failures at a younger old age than others, while others seem more immune from all of them -- they are on different parts of probability curves on each form of failure.

What we see is that these do not really come into play until an organism is beyond an age where their continued contribution to the population is beneficial to the care and raising of their children.

Thus each of these systems would have evolved to ensure that sufficient age was reached to provide the care needed, with variable results due to standard variablity within populations. There would be nothing to maintain a need to be older, especially when the same resources can be spent on progeny.

It is more noticeable in the human population than in other organisms as we have been able to reduce environmental causes of death (predation, disease, accident) which results in two things: births > deaths and more old people.

Enjoy.


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albertng
Inactive Member


Message 37 of 46 (368120)
12-07-2006 2:16 AM
Reply to: Message 36 by RAZD
12-06-2006 8:11 AM


Re: death by "old age" is death by one of many means, not just one cause.
In regards to aging, one should note that the germ lines do not exhibit any characteristics of aging nor do hydras show signs of aging, although they eventually die.

Irrespective of the fact that all things must die, why do most organisms age while some specices have seemingly eluded evolution?

References:
Kirkwood article in Nature volume 408
Martinez, Mortality patterns suggest lack of senescence in Hydra,
Experimental Gerontology, vol 33

Edited by albertng, : No reason given.


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Doddy
Member (Idle past 3986 days)
Posts: 563
From: Brisbane, Australia
Joined: 01-04-2007


Message 38 of 46 (384561)
02-12-2007 5:44 AM
Reply to: Message 37 by albertng
12-07-2006 2:16 AM


Re: death by "old age" is death by one of many means, not just one cause.
why do most organisms age while some specices have seemingly eluded evolution?

There are some interesting theories on this. Which ones have eluded evolution?

First, let me explain my views on death and ageing.

An organism is likely to die through some cause (disease, accident, being eaten or killed, starvation etc), but is unlikely to live forever when these things are present. It's like walking through a minefield - you might get a long way, but you can't keep going forever.

In fact, the pressure is to ignore how much food you need for the long walk in the future, and focus on avoid the mines now.

In the same way, there is pressure against repairing (at least perfectly. A cursory defence is useful) the cells against mutations and chemical damage. Why use energy to repair yourself to keep healthy and reproducing for 400 years, when that energy could be better used avoiding death from illness at 3, avoiding starvation at 14, having a healthy baby at 19?

To use energy for fixing those things would be useless if something else will kill you. So there is no way that the organisms with the capacity for longer lifespans will out-reproduce those who ignore it, under circumstances with accidental death and slow degeneration of age.

So, back to the question on why do some organisms age while others don't. It could be that those organisms are simple enough so that the maintenance of that organism is easy enough that it is achievable without too great a sacrifice. After all, it is easy to keep my desk clean from dust (being a simple structure), but the entire house, with all the complicated devices and fine areas to clean would be very hard to clean indeed, even with extra people at my disposal. So, the simple body plan of a hydrazoan would be easy to repair against mutations, but the complicated mammalian body would be far harder, even with the extra energy available (which would be better spent on other things).

ABE: It may also be that the smaller bodies are more vulnerable. With a body of say 300 cells, one cell that goes haywire is actually a large threat so energy should be used to prevent cancer. In a body of trillions of cells, the bigger threats come not from one haywire cell inside, but a trillion angry cells outside (predator) or billion cells inside (disease).

Edited by Doddy, : Added extra stuff


"Der Mensch kann was er will; er kann aber nicht wollen was er will." (Man can do what he wills but he cannot will what he wills.) - Arthur Schopenhauer

"Science can destroy religion by ignoring it as well as by disproving its tenets. No one ever demonstrated, so far as I am aware, the non-existence of Zeus or Thor - but they have few followers now." - Arthur C. Clarke


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Pharaoh205 
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Message 39 of 46 (434865)
11-17-2007 8:33 PM


spam removed
spam

Edited by AdminNosy, : No reason given.


  
Jarrod
Junior Member (Idle past 4040 days)
Posts: 1
From: Melbourne, Australia
Joined: 11-29-2007


Message 40 of 46 (437439)
11-30-2007 2:26 AM


I am assuming the OP was referring to death by aging.

"Aging is a product of evolutionary neglect" - Aubrey de Gray (1)

Short answer: No. It is far more important for an organism to reproduce than it is for it to live forever, or even a long time. Death is a byproduct of our biochemistry which evolution has not had enough selective pressure to fix.

While a longer lifespan has some obvious evolutionary advantages such as the opportunity to go through more breeding cycles and produce more offspring, there is a much greater selective pressure to simply reproduce at all; strictly speaking, from an evolutionary perspective an organism has to live precisely long enough to reproduce and pass on it's genetic information, and not a moment longer. Evolving long or unlimited lifespans is not a priority.

In addition, it is also difficult. The metabolic processes that result in aging are very complex; solving the problem of aging is a difficult one for evolution and natural selection.

(1) A very interesting presenation by the eloquent and entertaining Aubrey de Gray. Mostly OT, but it does cover the mechanisms of aging, and he also addresses this exact question regarding evolution and death at the end: https://www.youtube.com/watch?v=8iYpxRXlboQ

P.S. I would be interested to hear people's thoughts on the apparent positive correlation between life-span and species complexity.

Edited by Jarrod, : No reason given.


  
mobioevo
Member (Idle past 4021 days)
Posts: 34
From: Texas
Joined: 12-13-2007


Message 41 of 46 (440585)
12-13-2007 7:03 PM
Reply to: Message 7 by Modulous
11-11-2006 10:59 PM


Re: The Law of death
quote:
Why do bodies grow old and die? Would it not be evolutionarily 'stable' to live longer and have more children and look after them and have more children and so on and so on?

You should read about r/K selection theory as it deals directly with this question. An r strategist live hard and die young (much like a rockstar). They will use up all the energy they have acquired to produce as many offspring in the shortest perioud of time. Think about annual flower plants. They grow, flower, produce seeds, and die. Then the next year it is the same t hing.

A K strategist lives long and conservatively. They spend more time producing quality young and nurturing their young. They usually inhabit much more stable environments.

Here is a link to the wikipedia article on r/K strategies
http://en.wikipedia.org/wiki/K-selection

As for why we die of old age, it is the same reason why we have to buy new computers and cars eventually. The components wear out. I don't know if there was a study for this to see what strategy would be most beneficial, but from observations from life seems that what evolved was a mechanism for reproduction rather than repair. The 2nd law of thermodynamics is not going anywhere and the parts that make up our bodies are going to wear out.

As a side note, I always enjoyed though experiments of what would happen if we were not to die or live an extremely long life. I like to think in terms of morality rather than evolution because you would wonder what our thoughts of killing other non-mortal organisms would be like.

Edited by mobio, : added link


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mobioevo
Member (Idle past 4021 days)
Posts: 34
From: Texas
Joined: 12-13-2007


Message 42 of 46 (440588)
12-13-2007 7:09 PM


There was a study done, which I have forgotten the name, that shows that as bacteria divide the newly synthesized components will have a higher probablity of going into the same daughter cell, and the older components will go in the other daughter cell. This would create a cell that has all new parts, while another cell would have the older parts. In the study it showed that over time the cell that contains the older parts is less fit than the cell with the newer parts.
    
Modulous
Member (Idle past 180 days)
Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 43 of 46 (440721)
12-14-2007 9:53 AM
Reply to: Message 41 by mobioevo
12-13-2007 7:03 PM


Re: The Law of death
As for why we die of old age, it is the same reason why we have to buy new computers and cars eventually. The components wear out. I don't know if there was a study for this to see what strategy would be most beneficial, but from observations from life seems that what evolved was a mechanism for reproduction rather than repair. The 2nd law of thermodynamics is not going anywhere and the parts that make up our bodies are going to wear out.

It isn't about getting worn out since our components are continually replacing themselves. See also wiki:

quote:
Historically, ageing was first likened to 'wear and tear': Our bodies get weak for the same reason that a knife gets dull or metal rusts. 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. In fact, it is a defining feature of life that we take in free energy from the environment and unload our entropy as waste. Living systems routinely repair themselves, and, in fact, can build themselves up from seed. There is no thermodynamic necessity for senescence. (Nevertheless, the idea of 'wearing out' has so much intuitive appeal that even experts will lapse into thinking that way at times.)

http://en.wikipedia.org/wiki/Evolution_of_ageing

The current theory is Wilson's antagonistic pleitropy which I referred to in Message 6, though this is only partially validated at this time. One interesting thing is apoptosis or 'cell death' a process which cells kill themselves if they are diseased or faulty. This process goes a bit nutty in late life so that even healthy cells begin to kill themselves - this isn't 'wear and tear', it seems part of the natural development cycle of an organism for some reason.


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mobioevo
Member (Idle past 4021 days)
Posts: 34
From: Texas
Joined: 12-13-2007


Message 44 of 46 (440763)
12-14-2007 1:18 PM
Reply to: Message 43 by Modulous
12-14-2007 9:53 AM


Re: The Law of death
quote:
Historically, ageing was first likened to 'wear and tear': Our bodies get weak for the same reason that a knife gets dull or metal rusts. 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. In fact, it is a defining feature of life that we take in free energy from the environment and unload our entropy as waste. Living systems routinely repair themselves, and, in fact, can build themselves up from seed. There is no thermodynamic necessity for senescence. (Nevertheless, the idea of 'wearing out' has so much intuitive appeal that even experts will lapse into thinking that way at times.)

I would disagree with that statement. It assumes that the entire organism is an open system. Just because living cells can repair some decaying cellular components does not mean all cellular components are repaired.

Multicellular organisms can compartmentalize the effect of degradation on them. Having the arm fall off of an organism due to some accident will not affect the gametes and thus reproduction, but mutations that will occur in the DNA during spermatogenesis or in the eggs of females over their lifetime could make them sterile.

Unicellular organisms have been shown to compartmentalize their degrading cellular components by specifically segregating the older components into one daughter cell and placing the newly syntesized components into another daughter cell. It has been shown that the cells that have the older components are less fit than the cells with the newer components. I will try to find the paper of the experiment.

I agree that apoptosis and other programmed cell death has an impact on cell life and there may be a limit to age, but to disregard environmental impact would be a fallacy.


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Modulous
Member (Idle past 180 days)
Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 45 of 46 (440776)
12-14-2007 1:50 PM
Reply to: Message 44 by mobioevo
12-14-2007 1:18 PM


Re: The Law of death
I would disagree with that statement. It assumes that the entire organism is an open system. Just because living cells can repair some decaying cellular components does not mean all cellular components are repaired.

Right - but the question is why do repairs and replacements stop happening? It's nothing to do with wear and tear because (as far as I can remember) nothing exists of my body from 15 years ago to have worn or torn. It's all gone, all of it. It wore out a long time ago.

I agree that apoptosis and other programmed cell death has an impact on cell life and there may be a limit to age, but to disregard environmental impact would be a fallacy.

Nobody is disregarding environmental impacts...however the idea that cells are 'wearing out' over time like computer components isn't an accurate way to look at why we age.


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