Fundamental question: why do we age?

[LennoxLewis]

Cells are constantly being replaced at a high rate, but why does our skin wrinkle nonetheless? When you workout or are involved in any physical activity, and you eat enough protein, muscle tissue is being built and repaired. Why do reflexes slow? It's still the same or nerve channels being used... or is it for motoric reasons? Why do we go bald and/or grey?


Another question: I just read an article about regeneration, on how reptiles can regrow limbs and how we humans inprinciple have the knowledge stored in our body to do the same (a cut-off fingertip will regrow in exact the same state, including finger nail etc for children up to 10 years of age, but no more than that). So why has generation ability been lost in evolution? According to the author, it was for two reasons: one is because reptiles (and other more "primitive") animals have a much simpler build, therefore easier allowing regeneration. I thought that was a rather weak argument... if we can grow them once, why not twice? Second, the cells that induce regeneration (the ones we miss, i don't know the English word for it, "Blasteem" cells in Dutch if i remember correct) increase the chance of cancer which is a much bigger problem for primates like us, but not so much for reptiles.

 

[DaveC426913]

We age because not aging is not an evolutionary advantage.

Energy put into keeping us youthful after our breeding period is wasted energy that could better be put toward propogating the species.

 

[JonMoulton]

You might be interested in looking into this component of aging. There are many factors which contribute to aging, but lamin-A mutation causes Hutchinson-Gilford progeria syndrome (premature aging) and changes to the lamin-A gene are a normal part of aging.

Scaffidi P, Misteli T. Lamin A-dependent nuclear defects in human aging. Science. 2006 May 19;312(5776):1059-63. Epub 2006 Apr 27.

Scaffidi P, Misteli T. Reversal of the cellular phenotype in the premature aging disease Hutchinson-Gilford progeria syndrome. Nat Med. 2005 Apr;11(4):440-5. Epub 2005 Mar 6.

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

 

[DaveC426913]

A better way of looking at this would to ask the question "why do we regenerate as much as we do".

All things age and disintegrate. This is the default. Start form there and figure out what life has doen to forestall breakdown.

 

[Andy Resnick]

Cells are constantly being replaced at a high rate, but why does our skin wrinkle nonetheless? When you workout or are involved in any physical activity, and you eat enough protein, muscle tissue is being built and repaired. Why do reflexes slow? It's still the same or nerve channels being used... or is it for motoric reasons? Why do we go bald and/or grey?

Cells are not constantly being replaced at a high rate. Some divide faster than others- the epithelia lining our digestive tracts underoges renewal 1/week or so; the endothelia, muscle, nerve, are much slower or not at all- podocytes do not ever divide, for example. Aging can be viewed as an increasing inability for cells to make new proteins. The cause of baldness and grey hair are not totally understood- I know this because there is no effective treatment right now.

 

[The Dagda]

If you want the actual chemical answer you may be here a while. But as said in evolution a viable population is one that is in its environment, suited to producing the optimal numbers of animal in any given generation that will provide optimal ability to adapt; if nothing aged, then sooner or later an area would become overpopulated and the species would suffer and eventually die out as the area was over exploited. Evolution tends to eventually move towards a medium where death/birth are optimal given x environmental factors, but even then it is very much a blind endeavour.

Humans however seem bent on breaking that law of nature, and it can result in some pretty horrible consequences at least in certain areas of the world. Luckily Western countries tend to have established a ratio of two children roughly per generation when certain populations are reached, which eventually leads to if not stagnation then slow growth and even decline, the same cannot be said for some developing or third world countries, where the environment plays a large part.

That said human speciation is well adapted, it's just not perfect and easy to fit into the theory of evolution, as Darwin himself said. We seem well able to thin our numbers by war, famine, plague, and therefore death, the four horsemen of the apocalypse would be proud if they actually existed.

 

[LennoxLewis]

Thanks for the intelligent responses.

If a cheap way to prevent aging would be invented (or even something that increases the life expectancy to 100 years under middle-class circumstances), it would probably lead to a global famine and whatnot.



But basically, from what i gather, the benefit of reproducing is greater than constantly regenerating the body for energetic reasons? In our current society, this would not be a problem.

Can anyone tell me how much research is being done on for instance, being able to "reprogram" cells in such a way that skin doesn't wrinkle over age?

 

[Blenton]

We age because not aging is not an evolutionary advantage.

You would think that if you didn't age, then you would have more time to produce more offspring.

 

[DaveC426913]

You would think that if you didn't age, then you would have more time to produce more offspring.

This would be true if there were not a limited energy budget. But energy put towards not aging will take away from reproduction.

 

[The Dagda]

Thanks for the intelligent responses.

If a cheap way to prevent aging would be invented (or even something that increases the life expectancy to 100 years under middle-class circumstances), it would probably lead to a global famine and whatnot.
But basically, from what i gather, the benefit of reproducing is greater than constantly regenerating the body for energetic reasons? In our current society, this would not be a problem.

Can anyone tell me how much research is being done on for instance, being able to "reprogram" cells in such a way that skin doesn't wrinkle over age?

The aging process is better researched than ever, and as with most fledging sciences there are more questions than answers. It seems cells have a preprogrammed amount of times they will replicate encoded in things like the mitochondria (the battery of the cell) but it's far more complex than even this and we are facing challenges working out just what genes contribute to ageing.

Basically sexual reproduction and how fast it happens is intrinsically linked with death. Rats have a fast breeding cycle and don't live much longer than a few years. Humans have a slow breeding cycle but live far longer (again this is for reasons that aren't just environmental but sociological as well) It all links into this. If a creature breeds more frequently it will generally - more mutation, more mixing of DNA and so on - adapt quicker than if it breeds less, this could be advantageous, it depends how rapidly its environment changes. Another thing to consider is bacteria, now they reproduce asexually, but for single celled life it can be better to replicate quickly and without too much transcription and mixing of DNA than sexually reproducing. It all very much depends on the links between environment, adaptation and interactions between other species, as well as other less obvious factors.

 

[JorgeLobo]

Odd that no one has asked for biological definition of aging. Dagda's "more questions than answers" silly comment not withstanding, the most relevant research is not so much into aging per se, as into cellular fate and events.

Disagree with Dave - aging - whatever its definition - can't be assume to be a evolutionary advantage.

 

[DaveC426913]

Disagree with Dave - aging - whatever its definition - can't be assume to be a evolutionary advantage.

?? Did you misread? I'm saying it's not an evolutionary advantage, which is why we did not evolve longer lifespans (through whatever means it might hypothetically be done).

 

[The Dagda]

Odd that no one has asked for biological definition of aging. Dagda's "more questions than answers" silly comment not withstanding, the most relevant research is not so much into aging per se, as into cellular fate and events.

Why is that silly?

 

[JorgeLobo]

"The aging process is better researched than ever, and as with most fledging sciences there are more questions than answers"

Trite - and it's hardly a fledging science. Every science can fatuously claims more questions than answers.

 

[The Dagda]

"The aging process is better researched than ever, and as with most fledging sciences there are more questions than answers"

Trite - and it's hardly a fledging science. Every science can fatuously claims more questions than answers.

So you object because it's true? I see, and yes it is a fledgling science, how long have we been looking into the genetic causes of ageing, even psychology is older and I'd call that in its infancy too. Chemistry probably can claim more answers than questions, given it's age and the fact that much of its remit now falls under physics.

If anyone's interested check out pop science magazines, most of the issues are discussed there.

 

[DaveC426913]

yes it is a fledgling science, how long have we been looking into the genetic causes of ageing,

Certainly less than 50 years.

It continually astounds me when I remember that we have only known about DNA since the 1950's.

 

[JorgeLobo]

I object dadga because it is silly, fatuous and adds no value. If you've nothing of substance to say - why say it? LOL- I would expect you to be an expert on pop science.

True dave and your example is a good one. In every biological sciences, the last 50 years (more like the last 10 or 20) have brought exponentially more knowledge than before.

 

[The Dagda]

I object dadga because it is silly, fatuous and adds no value. If you've nothing of substance to say - why say it? LOL- I would expect you to be an expert on pop science.

And yet as silly and supposedly fatuous as it is, instead of addressing my argument, you've just resorted to ad hominems? Am I going to get an answer or just your opinion? If so I think we all know where you are coming from, you were just trolling. Well done I'm impressed...

By pop science I mean New Scientist and Scientific American, which I presume you think aren't worthy of consideration. Can we get with the program, or are you going to tell me you are an expert in this field and thus have the ability to judge all those lesser mortals, as wise and as well funded as you are?

 

[OAQfirst]

This would be true if there were not a limited energy budget. But energy put towards not aging will take away from reproduction.

Could you expand on this, please?

 

[JorgeLobo]

sorry dadga - you are apparently ignorant of the term ad hominem. I addressed your comment - not you. Understand? You statement was:
silly
fatuous
adds no value.
Please read carefully this time.

"Pop" science was your comment - not mine. New Scientist is a sensationalist rag. Scientific american is much better but more political. So these are your pop science journals?

What program? You've offered nothing so far.

 

[The Dagda]

sorry dadga - you are apparently ignorant of the term ad hominem. I addressed your comment - not you. Understand? You statement was:
silly
fatuous
adds no value.
Please read carefully this time.

"Pop" science was your comment - not mine. New Scientist is a sensationalist rag. Scientific american is much better but more political. So these are your pop science journals?

What program? You've offered nothing so far.

No I don't think so, you have explained your reason by trolling. 'nuff said. Can you answer my questions, what was wrong with saying there are a shed load more questions than answers in a fledgling science? Or not, if you can't then just say so, we're not on the clock here, or keeping score but you seem to keep insulting me without providing any reasoning. So reason instead of just throwing up logical fallacies... Is one rag wrong because you say it is? Is anything wrong or right by default? What are you saying please explain why? Program what does that mean? Are you the worlds greatest authority or did you just get out of the wrong side of the bed that morning, and just wanted to demonstrate you are the worlds leading expert on everything? Because you've lost everyone here...

 

[mplayer]

The definite answer to what causes aging is probably as complex as biological systems themselves, but here's my opinion.

The information encoded in your genome is responsible for building and maintaining the various parts of your body. This information is not duplicated with perfect fidelity throughout your life, for a large variety of reasons (some known, some unknown). Changes in this genetic information will eventually impair sub-cellular, cellular, tissue, organ, and/or organ system function. This process of biological degradation is referred to as aging, or senescence.

How does that sound?

 

[O Great One]

We age because when humans were created, the aging process was programmed into their DNA by the designers. This is why we only live to 115-120 years tops.

 

[mplayer]

We age because when humans were created, the aging process was programmed into their DNA by the designers. This is why we only live to 115-120 years tops.

Well that sounds perfectly reasonable...:yuck:

 

[BoomBoom]

I just noticed this thread and realized after going through all the back and forth meaningless bickering between Jorge and Dagda that nobody ever really attempted to address the Op's question.

Here are some theories out there (from wikipedia):

The cause for aging is most likely a combination of many factors, so there is no "smoking gun" cause.

Telomere Theory
Telomeres (structures at the ends of chromosomes) have experimentally been shown to shorten with each successive cell division. Shortened telomeres activate a mechanism that prevents further cell multiplication. This may be an important mechanism of aging in tissues like bone marrow and the arterial lining where active cell division is necessary. Importantly though, mice lacking telomerase do not show a dramatically reduced lifespan, as the simplest version of this theory would predict.

Reproductive-Cell Cycle Theory
The idea that aging is regulated by reproductive hormones that act in an antagonistic pleiotropic manner via cell cycle signaling, promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence (dyosis). At the same time, castrated animals, although living somewhat longer, still experience senescence, even in the absence of reproductive hormones.

Wear-and-Tear theory
The very general idea that changes associated with aging are the result of chance damage that accumulates over time.

Somatic Mutation Theory
The biological theory that aging results from damage to the genetic integrity of the body’s cells.

Error Accumulation Theory
The idea that aging results from chance events that escape proof reading mechanisms, which gradually damages the genetic code.

Evolutionary Theories
See Theories of aging in Senescence. These are by far the most theoretical; however, their usefulness is somewhat limited as they do not provide readily testable biochemically based interventions.
Accumulative-Waste Theory
The biological theory of aging that points to a buildup of cells of waste products that presumably interferes with metabolism.

Autoimmune Theory
The idea that aging results from an increase in autoantibodies that attack the body's tissues. A number of diseases associated with aging, such as atrophic gastritis and Hashimoto's thyroiditis, are probably autoimmune in this way. While inflammation is very much evident in old mammals, even SCID mice in SPF colonies still senescence.

Aging-Clock Theory
The theory that aging results from a preprogrammed sequence, as in a clock, built into the operation of the nervous or endocrine system of the body. In rapidly dividing cells the shortening of the telomeres would provide just such a clock. This idea is indirect contradiction with the Evolutionary Based Theory of Aging.

Cross-Linkage Theory
The idea that aging results from accumulation of cross-linked compounds that interfere with normal cell function.

Free-Radical Theory
The idea that free radicals (unstable and highly reactive organic molecules, also named reactive oxygen species or oxidative stress) create damage that gives rise to symptoms we recognize as aging.

Mitohormesis
It has been known since the 1930s that restricting calories while maintaining adequate amounts of other nutrients prevents aging across a broad range of organism. Recently, Michael Ristow has shown that this delay of aging is due to increased formation of free radicals within the mitochondria causing a secondary induction of increased antioxidant defence capacity.[29]