This makes no sense.

For instance, the statement:

> it's "an invention".

> As in natural selection decided at one point to introduce death. It really is the case that older lifeforms don't die. All mammals do though.

Natural selection is not an entity. It can not "decide" on anything.

What is here implied is that aging is an outcome of natural selection. Well, aging happens for many reasons, and it depends on how one defines aging (see Tom Kirkwood pointing this out decades ago); the implication meant here is that there has not been an optimisation towards perfection on the cellular (or organismal) level.

So, if damage occurs, the ideal situation would be that 100% of it is repaired. This does not happen. In theory it should be possible, but in actual practice, one will never have 100% repair, both on the DNA as well as protein/cellular level. Mutations will arise - that's for certain. There is no 100% perfect repair system. One can see this today with CRISPR-Cas9 promised as gene therapy tool, but whenever people ask about off-target damage and imperfect repair, those researchers dodge the question completely.

> if you study it, it becomes pretty obvious that in most cases reproduction and death are linked. Death is fundamentally a way to optimize reproduction, to control DNA variability and number of offspring.

I can not agree with this either. There are no specific death genes aimed at reducing life span per se (caspases/apoptosis has many functions, including formation of structure or killing virus-infected cells, among more functions). The main reason why reproduction is favoured, is because this is an evolutionarily stronger strategy, for most organisms. So more energy invested into offspring is more stable from an evolutionary point of view.

> The cells humans are made of are immortal, in the sense that human cells are capable of living and even reproducing indefinitely, if so directed by DNA.

Ultimately all cells are. Otherwise life would not be billion years old. The issue is not about immortality but damage and repair.

For instance, resetting telomeres in humans still would not make humans live thousand of years.

> Unfortunately this does mean that death is built into our cells and a lot of processes depend on aging and death.

No, it is not. What should that be? Describe that mysterious word "death". Which genes are related here?

In theory repair or restoration is possible; it is a finite problem. The question is how long it will take to improve on gene therapy on the nanoscale level. For instance, it should be trivial to enhance CRISPR-Cas9 to eliminate off-target effects; and enforce repair only happens in a guaranteed way. But achieving 100% is very hard - biology is nowhere near as strict as physics. Many genes are transcribed in a leaky manner; that has been one problem in biotechnology and synthetic biology as well. You can see this when you ask the Biobricks guys "which synthetic elements give us 100% control over genetic system xyz". Good luck getting them to commit to giving a single example here.

> At that point medicine will have to radically change and every tiny trace of every minor infection will have to be treated as a life threatening condition.

That's also not logical. If repair or genetic change is 100% or close to 100% accurate, why would ANY "infection" matter? In other words: why would infections be immune from genetic change? ALL viruses/bacteria use DNA or RNA. They are not exempt from ANY change here.

> ... the implication meant here is that there has not been an optimisation towards perfection on the cellular ...

This is why I'm limiting what I mean by death. Specifically to organism-wide senescence, loss of energy, and the death that follows. That senescence is very much programmed into our cells and is something that can be disabled (but as I pointed out, a lot of "downstream" inventions depend on it, so disabling it using current methods has disastrous consequences in practice)

We are also far short of the limits of human lifespan through damage. Old people die from "natural causes". What that is, exactly, is:

Step 1. the level of energy your metabolism produces within an entire cycle goes negative (ie. a 24 hour cycle, so there can be energy shortage during the day fixed during sleep, that doesn't cause this feedback loop to start)

When you're very young at this point homeostasis intervenes and refills your energy stores and go back to stage 1. However, that stops.

Step 2. In order to keep functioning your body effectively disables a system (there's dozens of ways this happens, from lowering blood suger to cutting blood flow entirely), reducing it's energy use. This starts with repair functions, then goes to immune response, and goes from there.

Mostly, at this point, we go back to step 1, and of course you stay alive while the energy level is dropping. But step 2 fixes less and less.

Step 3. Eventually your body has to cut critical functions. Digestion is not the first critical system to get cut, but let's say it is and keep things simple. You can disable digestion. Even just food intake itself (ie. keep water intake going). This will buy you weeks of energy, maybe months. But of course, this eventually causes more energy loss than energy gain.

Step 4. Your energy level drops to zero.

Very disconcerting is that I very much get the impression that moving from step 2 to step 3 is at least a semi-conscious decision. People decide, to an extent, when they die. Or should I say, people can consciously choose to delay it by a few months, at a cost. And certainly, they know pretty accurately when it will happen. I guess I'll find out sometime.

But this is not "damage". This is a combination of feedback loops, the way all "DNA programming" works. DNA has this death programmed in, and certainly in individuals you can achieve better outcomes by intervening externally. The time it takes for the mechanism to fire is also a parameter in our DNA, and obviously, the only way to implement this is with some sort of clock. Telomeres are thought to be part of the clock mechanism that does this, but they can't be the full answer.

Now you can say this is not "causing death". If anything, this is preventing it. And except for one major detail you're kind of right. That major detail is that increasing energy output is trivial, yet the system stops doing it (permanently increasing energy output is what happens during growth and temporarily increasing energy output is what happens during early aging). Your body restricts itself from that solution to the point that average energy use systematically decreases during your life after a certain point and that is what finally leads to a natural death, what finally fires off steps 2 and 3.

I don't claim that if you fix this there wouldn't be other problems, such as DNA damage, which would require their own solutions (even though we have that too. Crispr-CAS is restricted to short changes. But you can write an algorithm that, by combining literally tens of thousands of little Crispr-CAS cuts, repair essentially any DNA damage. And while that is probably not good enough a solution, you can easily demonstrate it works. Not working well enough, but working)

However, finding ways to do large scale fixing of DNA damage makes little sense until we can reset or disable the death clock.

> No, it is not. What should that be? Describe that mysterious word "death". Which genes are related here?

There are a great many genes involved, and many more regulatory factors. That's the problem. If it was one, "fixing" it would be easy. A famous example is p54, which puts a sort of absolute limit on cell age (when it fires, it activates other proteins that destroy the DNA, it fires off the self destruct mechanism of mitochondria and it rips open the cell membrane). There are also highly regulated genes that delay death under specific circumstances, like TERT changing the time at which such mechanisms will fire during cell division, for example.