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I know that we age because of errors in the cell replication process and these errors eventually leads to death.

If we exclude environmental factors, are there any other factors that can cause these errors? Is there for instance some kind of "programming" in our DNA of our death?

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Perhaps the best type of study to examine the role of genes (DNA) in human aging are twin studies. They have either: the same DNA (monozygotic, one egg, "identical" twins (MZ) ) or similar DNA (dizygotic twins, two eggs (DZ) ) and are perhaps exposed the same, or different environments. I won't repeat the information in the link, above, but studies of this type guide that our DNA is not an absolute roadmap of our future.

DNA damage can be caused by exposure to excessive radiation, viruses, chemicals and just 'random events'. Cells and tissues can also be damaged by oxidative damage - literally oxygen and related molecules that are produced within the body and can react with components of cells (e.g DNA, proteins and the lipid cell membrane). The accumulation of these oxidized products in and around the cell disrupts tissue function and leads to many of the symptoms of aging, a process called sensescence.

We obviously cannot avoid having oxygen around us. In the same way, our cells need the sugar glucose as a source of energy. Glucose can spontaneously react with proteins and lipids to form advanced glycation endproducts (AGEs). AGEs are pro-inflammatory. In diabetes, where blood glucose levels may remain at higher than normal for extended periods, the formation of AGEs can lead to nerve and kidney damage. The chemical reaction that is occurring is the same as when you toast a piece of bread or fry a steak. So paradoxically, two of the ingredients essential for life - oxygen and glucose - are slowly but surely disrupting our body's function over the course of decades. Although the body can replace some of these damaged proteins, they accumulate over time, as evidenced by the increasing lack of elasticity of older skin as collagen proteins are cross-linked.

Regular exercise, good diet and friendships all add to mental and physical health, quality of life and longevity. So, to live a long time, don't stress, have ONE slice of cake and make new friends who will exercise with you.

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It is important for organisms to be renewed. These organisms have less wear and tear, they are modified through evolution to better fit the current environment, they are more likely to have healthy offspring that they can look after. It must also be considered that genetically we must be optimal in anyway that confers our continued survival as a species. So we should remain alive only for as long as it benefits the species (i.e. raising our young) and die once we are less help and more burden.

So with all that in mind, why do errors or mutations occur? Well we need optimal amount of mutations that allow us to constantly evolve to adapt to the newest environment. If we don't evolve, we die. Keeping our DNA mutation free is too costly anyway for it to confer a survival benefit of the species (rather than the individual). It would require far too many error checking pathways which themselves would be in need of being checked. So yes our cells have programming to allow mutations (by not having completely successful countering techniques) as it is beneficial.

Our cells themselves can only replicate so many times due to the length of telomeres. These are little bits of DNA at the end which after each cycle shorten (as we can't replicate DNA at the end efficiently). After a certain amount of replications a cell is destined to die. An enzyme exists, telomerase, which resets this by lengthening the telomeres. However over expression of this enzyme leads to cancer. Again, it is important for us to mutate in order to evolve but too much is harmful. The same argument applying that it is too costly to be perfect and not mutate.

Logic dictates that if humans survived for much longer, over population would impact on our own survival.

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This is the answer that is the most adressing my question. I see that DNA controls cell replication, but allows in its own code mutation. But in the end the bad replication of the edges of the DNA is more an efficiency that something "coded to make us die". – capricorn Apr 15 '14 at 8:10

Obviously, it is conceivable that DNA could be so damaged that the organism dies. Trivially, blasting cells with radiation will cause rampant DNA damage, which will trigger p53 and lead to the cells suiciding (apoptosis), this is a "deliberate" (so to speak) mechanism to manage cancer risk.

In practice, the reason DNA damage leads to death is usually not because the information is corrupted and important functions are abrogated, but because the mutations lead to cancer, and the cancer leads to death.

However, most people don't die of cancer. A lot do, especially in developed countries, but most often people die because of infection or heart failure. Other major causes include neurodegenerative disease (neurons dying) and diabetes.

If you are asking whether in some part of the DNA, there is a bit saying Maximum_Age = 85 (by analogy to programming constants), I don't think anything of the sort has been found. The body naturally has finite lifespan because things break, this is extended up to a point because the body also has mechanisms to repair some kinds of damage.

Why not repair all kinds of damage? Why are the repair processes imperfect, and cannot maintain the organism indefinitely? Good questions, without good answers known to science.

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