why our body is able to self heal but it will stop working and let us die when we get old?
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Parts of your body (cells) are constantly dieing and have to replicate. Like every 7 years you have a “new” body. These copies of cells can have errors (caused by environment factors like radiation, UV light, etc). So we slowly get every time we need new cells a less good body until he is no good anymore and can not live anymore.
As you get old, your body becomes less and less good at taking what you eat, breathe and drink to get back to full capacity.
There are also some vital organs that are easier to heal than others. As they all start degrading faster than they can heel, they eventually shut down.
Think of the regenerative ability of your body like a car engine. When we are in our younger years, our body is like a car engine that is well-maintained. It runs smoothly and efficiently, and can handle any bumps in the road – just like our body can heal and repair any injuries sustained. As we age, our “car engine” suffers from wear and tear and its performance deteriorates.
That’s the ELI5 version, without getting into decline in cellular activity, decrease in the ability to repair damaged proteins, etc.
Inside your cells, there is a structure called a telomere chain. Think of it like a ladder, with many, many rungs
When your cells are damaged, they divide themselves, the damaged version of the cell dies, and the newly formed non damaged cell takes over. Whenever that happens, the telomere chain in that cell is one rung shorter than the original cell.
When the telomere chain runs out, cells no longer divide to replace themselves. So the cells get more and more damaged over time, they aren’t replacing themselves, and eventually the system breaks down and you die
Your body is just a machine that your DNA uses to reproduce/procreate. When you are young, it is in your DNA’s best interest to heal your wounds. When you are past reproductive age, your DNA doesn’t really care if you live or die (this is not 100% accurate, but simple enough for ELI5). So your body (guided by your DNA) does its best to make sure you get to reproductive age, then kinda stops caring what happens to you.
Some of it is wear and tear (scars, mutations, etc) but a lot of it is evolved. There’s structures on our chromosomes called telomeres that protects the data, but they shorten each time the cell reproduces which effectively tracks age. The shorter the telomeres, the more likely mutations occur which both results less efficient cells and cancers.
There’s a lot of hypothetical reasons why it’s beneficial not to be immortal but dying of old age seems pretty much hard programmed to happen as you get near 80 (some variance based on healthy lifestyle and genetics of course)
It’s evolution.
You only need to be alive long enough to procreate. And sure, you can have a few decades of being viable for that purpose. However, as you get older and beyond procreation you become a drag on evolution. It costs to keep you alive, and that cost is better spent on the next generation.
Having typed that out, it seems a bit harsh. But hey, I didn’t make the rules.
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