Schneibster

From an evolutionary point of view, in order for genetic replication to lead to evolution in the first place, new variations must replace the old, which implies that the older variations must disappear. Evolution could not take place unless this happened, by some means or other.

DNAunion, thank you for your information on teleomeres and teleomerase; I had not heard the part about the DNA polymerase not being able to make it to the end of the chromosome as an explanation of the need for teleomeres before. Most interesting.

Dark Knight Bob

No. We don't have these people around today. For the DNA to vary enough to protect neural tissue from free radicals would in itself be such a grand undertaking that a few thouasand years wouldn't get rid of such people. In fact they would undoubtedly be around in their droves not getting any cancers no matter how much radiation and living to grand old age of 950.

Oh i know that some areas do regenerate but we're talking about the majority of tissue here.(afterall the nervouse tissue has to grow in the first place to get there so some left over growth process would be expected) And the odd patch up of nerves here and there that could easily happen. But there is no system in place to repair the overall nervous system and what repair functions do exist haven't a hope to compete.

In such areas the effect overall is negligable so I didn't really see the point in confusing the issue.

The key point here is that stem cells need to be injected. The body won't spontaneously create them and even then it can only make what it has the information for so damaged DNA will still be created and the downwards spiral towards inevitable death will occour.

But of course some politicians have this bizarre hang up with stem cell research. I'm glad that your freind is having success with his treatment. at least some people are benefiting from it.

DId noah have some freak mutation that made much more stem cells in his body for some bizarre reason? Well I think that's putting hypotethical solutions towards an arguement that can fall down on simple historical accuracy.

|2eason

FYI:Reith lectures from 2001

This series of lectures goes over the technical obsticals of overcoming the aging process.

Agemegos

Are you sure? Then why don't I look as old as my mother? My DNA is at least as old as hers.

And if cellular mechanisms can repair DNA during reproduction, why can't they do so ordinarily?

On the whole, I think that Medawar's theory of ageing (in terms of pleonastic genes with age-dependent effects) is far more convincing.

Agemegos

So what? Stasis is no more impossible than extinction.

What actual mechanism prevents evolution from grinding to a halt?

Schneibster

Stasis in a changing environment is extinction.

None save environmental changes.

Dark Knight Bob

Ok first. You're not you're mother. You don't look like her exactly to start off with

Second i'm assuming you're comparing your current age to what your mother looked like when she was that age. Afterall to be the same age of your own mother is impossible.

third you lived a different life to her with varying degress of environmental factors. different food, different health, different exposure to sunlight.

forth. you are a split between your mother and your father not your mother alone.

fifth. the destruction of DNA is random. It's merely a statistical fact that you will over time get damaged DNA that is required for repairing your skin etc. it does not mean you will get the same parts of your dna damaged nor that they will be in the same order.

we have a set number of stem cells used to create us when we develop. Why this is i can only guess. possibly to stop us growing continually in some bizarre cancerous growth of random apendages. stem cell treatement is a localised treatement used for repairing small areas so it is not comparable to the growth during early life.

Also as i said they can only repair what they have information for. If you start off with a 100% healthy template then it gets damaged to 98% that 2% variation will now be assumed by the repair "system" to be an accurate model and will happily copy that 2% damage into the new tissue. Then when it next gets damaged it will be for instance 96% accurate. continue this progression over time and eventually you will have DNA that has bad copies all over the place and without being able to tell what the original DNA was your body cannot repair the damaged DNA. I'm sure in the future with gene therapy it will possible to identify any 100% healthy DNA in your body and with proper treatment (thogh no doubt expensive) you will be able to have healthy DNA replace the damaged and stay young but at the moment you're stuck with dying at around 80 years of age and have your body fall apart on you just like everyone else.

Sorry to be the bearer of bad news, But that's life.

You're talking about different people with different genetic makeups. Again put it into a statistical model and everyone's lifespan is still restricted by DNA degredation just at various rates. There are exceptions such as people living as old as 120 but notice how these people still die and that these examples are the EXTREME. They are right at the edge of statistical plausability.

If you were to apply the possibility of havign someone live to the age of 950 under these conditions then you would most likely have to have a population around something like 1x10^20 or something equally ludicrous.

There isn't enough room on the planet ot fit that many people in. If you wanted to be a creationsit, you'd probably come up with some ludicrous notion that this is why the flood happened, because god saw that there were 50 trillion trillion humans on the planet and needed to do some in-house trimming so he got noah to build an ark etc. etc.

The non-static nature of the environment. There are a few species that exist who have on evolutionary terms come grinding to a halt but these are because their environment hasn't changed and therefore their needs haven't changed. It's purely a mathematically stable system.

epepke

The nervous system does regenerate, albeit slowly.

The big problem with the brain is that it would fill up. The brain is wrinkled and densely packed, but still it requires enough of a cranium to cause some serious problems with childbirth. It would be nice if you could just reformat parts of it, but it doesn't seem to work that way.

Besides, everyone would probably kill you before you got to 950 years because you'd be telling the same stories over and over again.

DNAunion

They do. But nothing is 100% accurate.

Even during DNA replication 'tons' of copying errors occur. The first line of defense is the DNA polymerase enzyme itself: when it adds a nucleotide to the growing polynucleotide chain, it pauses and checks to make sure the correct nucleotide was added (based on the rules of complementary bases). If the wrong base was added, the DNA polymerase excises that one nucleotide and then adds another one before proceeding. But even then, some of these point mutation errors occur (as well as several other types, such as slipped strand mistakes).

After DNA replication is complete, other enzymes in the cell continually monitor the DNA, scanning over it and checking for physical deformities, such as a slight bulge that would occur if two purines were accidentally hydrogen bonded together. They then make a cut in one of the strand (the one with the error), and then DNA polymerase comes back and adds more nucleotides to fill up the space. But again, this doesn't catch all errors.

In addition, the DNA in cells is continually being damaged by water. Bases can be switched by being deaminated, for example; and in fact, sometimes whole bases are lopped off at the glycosidic bond that holds them to their pentose sugar (deoxyribose).

Unfortunately, the cell's replication and maintenance is not 100% accurate or 100% fast (i.e., even if it were about to fix an error, it is possible that another cell division is begun before the repair is complete).

So with 100 trillion cells in your body, even an average error rate of, say, 1 in ten billion base pairs per cell division could lead to a relatively large number of changes in the DNA of somatic cells. Over time, this damage accumulates and your cells, then tissues, and ultimately organs and organ systems can suffer.

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Then there is the damage mentioned before concerning telomeres. We don't have the enzyme (telomerase) needed to extend them, so our telomeres shorten during every cell division. Thus putting a limit on the number of times a cell lineage can undergo division.