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Author Topic:   Devolution (from The Fall) and "No New Information"
slevesque
Member (Idle past 2721 days)
Posts: 1456
Joined: 05-14-2009


Message 46 of 52 (518956)
08-10-2009 3:40 AM
Reply to: Message 45 by Meddle
08-10-2009 3:23 AM


Of course, I did not to make it seem as though we die becuase of one reason. It has multiple factors. Still, mutations accumulate as we grow older from the very first cell.

Well our chromosomes have two copies, which means mutations can be eliminated during mitosis as the chromosomes cross over, negating the effects of Muller's ratchet. Unlike bacteria for example, where only one copy of the genome exists

Mutation are not really eliminated, since one of the daughter cells will always end up with the mutations that the initial cell had. Because, all in all, all the chromosomes will end up in one of the two cells.


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Theodoric
Member
Posts: 5954
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.0


Message 47 of 52 (518977)
08-10-2009 7:58 AM
Reply to: Message 44 by slevesque
08-10-2009 1:32 AM


The accumulation of mutations in our cells as they replicate and we grow up is what ultimately causes us to die, the software of our cells becoems so corrupted by mutations that systems and organs start to fail, etc. etc. This process starts from the very first replication of the very first cell, not just from after 3 or 18 years of age.

I still do not see how you can make a subjective statement that a 3 year old has gone "downhill" from a newborn.


Facts don't lie or have an agenda. Facts are just facts
This message is a reply to:
 Message 44 by slevesque, posted 08-10-2009 1:32 AM slevesque has responded

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 Message 48 by slevesque, posted 08-10-2009 3:08 PM Theodoric has responded

    
slevesque
Member (Idle past 2721 days)
Posts: 1456
Joined: 05-14-2009


Message 48 of 52 (519021)
08-10-2009 3:08 PM
Reply to: Message 47 by Theodoric
08-10-2009 7:58 AM


Of course, I mentioned that genetically speaking, it has gone downhill. The DNA message with the acumulation of mutation, loses its meaning and so eventually becomes 'incomprehensible' for the cells as we get older.

Genetically speaking, this is not a subjective statement.


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 Message 47 by Theodoric, posted 08-10-2009 7:58 AM Theodoric has responded

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 Message 50 by Wounded King, posted 08-11-2009 4:51 AM slevesque has responded

  
Theodoric
Member
Posts: 5954
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 3.0


Message 49 of 52 (519023)
08-10-2009 3:18 PM
Reply to: Message 48 by slevesque
08-10-2009 3:08 PM


The DNA message with the acumulation of mutation, loses its meaning and so eventually becomes 'incomprehensible' for the cells as we get older.

I have an uncle that just turned 91. I do not think his DNA is incomprehensible.


Facts don't lie or have an agenda. Facts are just facts
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Wounded King
Member (Idle past 2175 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 50 of 52 (519073)
08-11-2009 4:51 AM
Reply to: Message 48 by slevesque
08-10-2009 3:08 PM


Of course, I mentioned that genetically speaking, it has gone downhill. The DNA message with the acumulation of mutation, loses its meaning and so eventually becomes 'incomprehensible' for the cells as we get older.

Genetically speaking, this is not a subjective statement.

I think you are wrong. Not in that mutations can accumulate but in the idea that as people get older their DNA becomes incomprehensible to their cells. In such an instance the cell would simply die in many cases. Alternatively such mutations could give rise to cancer, which certainly can cause death but doesn't sound quite like what you were saying.

The link between cellular senescence, when cells stop replicating due to telomere shortening or severe genetic damage, and aging is not well understood. The fact that a lack of telomerase, an enzyme that maintains telomere length, is associated with progeria is highly suggestive, but points more towards a failure in the stem cells specifically rather than a general cellular degradation. Telomeres are also not 'DNA message' in the way you describe. So one of the clearest genetic links to aging is not to any problem through mutation scrambling the message in DNA but rather an inbuilt limitation of cellular replication.

As I say this can be a result of genetic damage as well, but of major things like double strand breaks, not a slow accumulation of small mutations.

To reiterate, I don't disagree that the genome of individual cells in an organism will diverge over time as it ages from its original zygotic genome. What I disagree with is the assumption that this is a major mechanism involved in aging. For individual cells it might work this way and such cells would then apoptose, but the subsequent aging and degeneration of a tissue would be due to a failure to replace these cells, a breakdown in the stem cells. You might make a case that the failure of stem cells was due to accumulated mutations causing them to senesce.

So I think your model of aging is highly flawed.

TTFN,

WK


This message is a reply to:
 Message 48 by slevesque, posted 08-10-2009 3:08 PM slevesque has responded

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 Message 51 by slevesque, posted 08-11-2009 10:38 AM Wounded King has responded

    
slevesque
Member (Idle past 2721 days)
Posts: 1456
Joined: 05-14-2009


Message 51 of 52 (519103)
08-11-2009 10:38 AM
Reply to: Message 50 by Wounded King
08-11-2009 4:51 AM


Of course, I'm not an expert on this subject, and I know that the process of aging is not well understood even today.

As I've also said in another post, I do not intend to make the process of aging and death a simplistic one with only a single factor. Multiple things come into play and eventually the effects add-on to bring the organism to be unable to maintain it's activity any longer.
I did not intend this as a model of aging, but only a model of one of the factors of aging.

As you and others have mentioned, there are mechanism in the body who prevent as much as possible the accumulation of mutations as we grow older (controlled death, etc.). These would be analog to some sort of 'natural selection' inside the body.

The 'inbuild limitation of cellular replication' is aso interesting, although I have not much knowledge on it. But I would wonder why such a mechanism would even develop in evolution. In oher words, what is the evolutionnary advantage of it if its main purpose is to limit our cellular replication and make us die ?

Also, I would also think that stem cells are not exempt of mutation accumulations as we grow older, which would lead to the breakdown you mentioned, I have no idea of how stem cells replicate and if they do in an asexual manner (well, probably I would guess), so maybe they can avoid mutation accumulation.

Finally, this is not my field of expertise in french, let alone in english, So my knowledge as well as my vocabulary is limited and I would like you to consider this when replying on this subject.


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 Message 50 by Wounded King, posted 08-11-2009 4:51 AM Wounded King has responded

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Wounded King
Member (Idle past 2175 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 52 of 52 (519157)
08-12-2009 5:24 AM
Reply to: Message 51 by slevesque
08-11-2009 10:38 AM


The 'inbuild limitation of cellular replication' is aso interesting, although I have not much knowledge on it. But I would wonder why such a mechanism would even develop in evolution. In oher words, what is the evolutionnary advantage of it if its main purpose is to limit our cellular replication and make us die ?

One popular theory is that it is a way of limiting cancers. The reactivation of telomerase is a common step in the progression of the majority of cancers.

It is important to keep in mind that evolutionary pressures are not towards making us live forever, merely towards producing offspring. After one passes the age historically associated with having children, since lifespans have bben considerably shorter for most of human history, there are not likely to be many evolved adaptations to old age.

TTFN,

WK


This message is a reply to:
 Message 51 by slevesque, posted 08-11-2009 10:38 AM slevesque has not yet responded

    
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