Eli5 why can’t organisms regenerate tissue indefinetly, why do we die of old age
In: Biology
Maybe there is a deeper topic here. Our body’s primary goal is to reproduce. We see in many life forms that, after reproduction, there’s no more push to keep living. After our physical peak for fertility, our body starts to decay. There is no reason for our bodies to have the ability to naturally live forever, going by the former logic. From there it delves into asking why forms of life’s only goal is to reproduce in the first place. If we could live forever, there would be no focus on reproducing for the purpose of continuing life. So what would the goal life evolutionary pushes for be? Why is life’s goal in the first place to continue? Why does life really even exist? What’s the end game?
Because evolution doesn’t require it, and it some ways it’s anti-evolution. Once a creature breeds and generates offspring that survive, it has done what it needs to do to perpetuate the species. Of course, making more offspring helps, but at some point they don’t add much more genetic diversity into the pool. Random diversity helps the species adapt to changing conditions. Species that can’t adapt well or rapidly enough tend to die off.
In the meantime, you’ve got old farts using up the resources that could be used by the new generation(s) instead. And as /u/sirbearus points out, mistakes are being made, both within the old coot’s body and within their ability to successfully create and support viable offspring.
If there was an overwhelming evolutionary driving force that favored oldsters, then it would probably (slowly) happen through the process of evolution. Eventually. Things like DNA, RNA, and protein synthesis might need to create error correcting processes that are virtually infallible, but don’t inhibit evolutionary diversity.
**TL;DR** – Making new animals is a better evolutionary “strategy” in the world we live in.
Telomeres are little bits of dna that protect our dna in replication. When our cells replicate, a little piece of the telomeres falls off. Eventually there are no telomeres left, and little parts of our essential DNA falls off and we are unable to replicate properly. With cloned animals like Dolly the sheep, they already have shortened telomeres depending on the age of the animal from which they were cloned, and therefore they start life as if they were aged quite a bit.
Some life forms have very long telomeres that lets them live longer, others have the ability to repair telomeres that causes them to not age at all, or age for unrelated reasons.
Here’s an article on species that have special aging properties:
https://en.m.wikipedia.org/wiki/Biological_immortality
Think of your body as a vehicle for your DNA to replicate itself. Your body’s goal is to live long enough to pass your DNA on to your offspring. The DNA is in the driver’s seat here, not your body. Your DNA doesn’t really care if you die at 50 or 70 or 90, because you’ve already had kids at that point.
The simple answer is errors. There are errors that occur in every system. You would think for example that computers don’t have errors but they do.
With biological systems the errors tend to not be able to be corrected consistently. The errors I am referring to are ones that occur with DNA replication and with cellular division. These errors accumulate over time and render the problems we association with old age.
Humans, experience wear and tear, joints wear out. There is not a system inside us for replacing the disks of the spine etc.
Other parts of our body, like the interior of the mouth get damaged and generally repair just fine.
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