why do living things have to die?
In: Biology
Many ways to answer this. Of course you got the philosophical aspect, but you tagged biology. But even in biology, you got the evolutionary perspective and the mechanistic perspective, so sort of the ultimate vs proximate “why.” Not to mention that even the latter has sub sections like physiological (whole organism so organs and such) vs cellular (cells dying without being replenished) vs molecular (like accumulation of epimerized amino acids and misfolded proteins).
On the evolutionary platform, death is necessary for evolution to take place at all, but that’s talking about complete invincibility. Otherwise you’d quickly saturate a given region in terms of space and resources leading to a cap on reproduction and bam (not to mention that having all species being invincible means you break the carbon cycle and that’s a whole other issue). However when talking about natural death being out of the equation but other deaths like accidents, murder and predator attacks, then the cap wouldn’t be on reproduction per se but on reproductive rate, so the progress of a species would be much slower. So while I cannot say species evolved death itself because that’s another topic (mechanistic platform), I can say they evolved different rates of deaths (average life spans) that are optimal to to their species’ environment.
On the mechanistic platform (I’ll focus on humans but this applies to a lot of species), we die because we age or because we are not invincible, as organic materials are fragile and our whole body has systems that are very fine tuned and dependent on each other, and the failure of one leads to the failure of the rest. Aging is a complicated process with several factors at play. The ends of each chromsome, called telomeres, gets degraded progressively each time the cell divides. Eventually the degradation gets to the actual sequence you care about and the cell is no longer viable. This is a very basic biological clock for the life of a cell. But aging affects the whole organism. Cells get damaged due to all sorts of reasons, like UV from sunlight and oxidative stress from metabolism alone. And when damaged a cell often commits suicide. We don’t have an infinite reservoir of cells, some specialized cells have only a limited number of stem cells. And when the we run out, renewal runs out. Besides that, you have many many processes that affect us gradually at the big picture level. Like nephrons (filtering units in the kidney) get less and less over a life time. These are relatively big structures made of many many cells so if they’re gone they’re really gone. Then you have things like atherosclerosis, plaques accumulating in your vessels, hardening them and narrowing them. You get strokes and ischemia and die from heart or brain issues. Or you may get proteins aggregating just due to random chance of misfolding, this happens in the brain and almost everywhere else. And we’re horribly bad at dealing with aggregates so they end up killing cells and you eventually. Then you got random mutations that are bound to once hit critical genes that then cause cancer. I barely even scratched the surface here, fixing a cell by allowing it to renew its telomeres has been investigated before. But the risk of cancer is too high. And even if it wasn’t, we got a million other things that are bound to go south over a lifetime. We’re simply not built to forever, if you want to be immortal you have to change your body altogether.
Edit: added some info
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