Death sucks; it’s ugly, smelly, often physically and emotionally painful to ourselves and others, and is just an all around shitty thing we’re all forced to do.
So what’s the deal? Why does all life seem to need to die? Why haven’t any truly immortal organisms evolved by now?
The answer is basically cancer. If you’ve studied cancer, you’ll note the unifying effect of all forms of cancer is runaway cell replication, where an unhealthy cancer cell will essentially replicate until there’s no longer enough room for healthy cells to fulfill their normal functions in our bodies. In effect, cancer cells outcompete normal cells until you get tumors which can eventually choke out vital organs and kill the entire organism.
Biological immortality (as in never dying of old age, not meaning “invulnerable”) is a lot like cancer; such a species would continue to replicate until they choked their environment and ultimately starved themselves to death. It’s basic math in the end – finite resources in a finite environment can only sustain growth for so long.
Thus, when life was first evolving from non-life, over vast expanses of time not really comprehensible to us, this biological calculus played out over many iterations inside the primordial soup that was the oceans of our planet. Primordial cells didn’t “learn” to die to prevent the exhaustion of their resources (there is no intelligent design in evolution); the ones that didn’t die simply failed to pass their genetics forward in time because they starved to death in a comparatively short period – similar to a runaway algae bloom in a small pond killing itself overnight due to oxygen starvation.
Interestingly, death is not necessary in any way biologically other than the evolutionary selection pressure I just mentioned. The cellular machinery that makes up our bodies is actually quite strong in terms of its potential; it’s just currently a jumbled mess and lacks any intelligent efficiency involved in its formation – the human body is a shining example of this “bare minimum” to get the job done, despite its apparent sophistication. If we had designed our bodies instead of the passive selection pressures of evolution on Earth, it almost certainly would be vastly superior, more efficient, and functionally immortal. Of course, we’d need the benefits of a post-scarcity society to support such proliferation without the environmentally-sustainable benefits of death.
Another reason death exists is the complexity behind repairing damaged biological matter. Believe it or not, it is far, far, simpler mechanically to create an organism (replicate, be born, grow, etc.) than to repair a significantly damaged one. For example, the process of growth in a human embryo is entirely driven by instructions derived from DNA encoding. Although complex, DNA encoding is something we can and have wrapped our minds around. However, say an organism was damaged by radiation poisoning and the DNA replication instructions were essentially destroyed or corrupted. How do you even begin to repair the damage? It’s similar to burning a piece of paper – is it easier to reverse all the chemical and physical changes the paper underwent? Or is it easier simply to make a new piece of paper from a tree?
Evolution follows the simple path of selection pressure, which is also the path of least resistance. Therefore, death is a convenient solution to both environmental resource depletion and biological damage. But that doesn’t mean death is inevitable, not at all. It merely means we evolved to die for profoundly important reasons, and that if we ever escape this biological shackle prior to achieving a post-scarcity state, we damn well better be ready to live up to the responsibility.