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This thread deals with the topic of how and why we age. Actually, I would much prefer to narrow it down to "why" we age, but for reasons that we shall investigate, this might not be practical.
To understand why we age is one of the biggest remaining mysteries in the biological sciences. Should someone come up with the answer, her name would certainly go down in history. Biologists are aware of that of course, and over the years there have been a huge number of theories on aging.
To understand why we age, two basic strands of theories exist:
(A) We age, because our systems break down over time (DAMAGE theories)
(B) We age, because there is an inbuilt mechanism that tells us to die (PROGRAM theories)
Not only for scientific but also for philosophical and religious reasons it would be extremely interesting to find clear evidence for (B). In fact, finding such evidence should make most readers her very happy indeed. However, such evidence is notoriously hard to produce. The famous "death hormone" has yet to be proven to exist. Some genes do affect lifespan dramatically, but it is more likely that their presence (life genes) or absence (death genes) actually impact on the effectiveness of repair.
This links us back to (A) and the huge number of damage theories (or rather damage observations) that have been advanced.
Some prominent ones include:
- free radical theory of aging: aging is the accumulating damage that free radicals cause
- somatic mutation theory: aging is the accumulating damage that occurs in the DNA during a lifetime
- wear and tear theory: rather than a cellular process the main cause of aging and death is the wear and tear that occurs in our vital organs over time
I personally would put my money largely on the free radical theory. There are other theories out there, usually describing the symptoms of aging. The "lipofuscin" theory is one of the oldest. The "crosslinkage theory" was popular in the eighties, the "de-methylization" theory is a younger candidate. More on these below, and all of them need to fit into the picture if we ever come up with a unified theory of aging.
We can see now, the question of "why" we age is hard to separate from the "how". There is another related question that for our purposes is extremely important:
How and why do we die?
The HOW part is rather difficult to answer. People do not die of old age. (It could even be argued that there is no conclosive definition of death). Old people leave life more easily than young people do, because their biological defence and maintenance does appear less rigorous. Statistics are telling. This of course leads back to the theories above.
The WHYpart is even more controversial.
Let us stick with a Darwinian theory of evolution for the present purposes: Does it make evolutionary sense to die? I contest that it does not, but let us come back to the question later.
Obviously, all these topics are linked.
For the present purpose, contributions are invited on the following eight (of course) points:
> (AA) Present a single DAMAGE - based theory
> (BB) Present a single theory leaning towards the PROGRAM theory
> (AC) Comment on or discuss a single DAMAGE based theory
> (BC) Comment on or discuss a single PROGRAM based theory
> (EE) Comment on theories about EVOLUTION and aging.
> (FF) Comment on the relationship between two or more theories
> (GG) Comment on aging theories in general
> (XX) Comment on the discussion in general or another point of interest
When you reply, please indicate in the first line the point that you would like to address by number and the theory/ies that you are addressing. (No need to stick with the colours, they are just for easy reference in this post)
Contributions and questions from everyone are very welcome!
Some literature:
Tom Kirkwood; The time of our lives, } one of the most prolific works, and one that we will surely come back to.
Robert Arking; The Biology of Aging, } a relatively comprehensive yet very readable overview of aging as a phenomenon
Robert Ricklefs / Caleb Finch ; The Biology of Ageing -A Natural History } another fairly good overview by established authorities
(These are the ones on my desk right now, I am sure there are better ones, feel free to recommend them under point (8).)
Thus as always: "aging theories" online, indexed by GOOGLE !
The subjects was also briefly adressed in numerous other places in this forum for example in "Scientific Reviews On Aging"
Edited by kperrott, 01 August 2003 - 03:29 AM.