Argthtjtr

In my research on how I could get elves to live the time spans I wanted them to live, I came up with this solution:

Every elf generates while still developing inside the womb of the mother copies of his embryo which get stored somewhere in his body. Each time the elf reaches its equivalent of 60 years (human age) a hormone causes one of the embryos to share its DNA and within the next 3 to 4 years the elf gets his whole body replaced by the young body code the embryo has stored. during these 3 to 4 years the elf is very vulnerable and will sleep 90 to 95% of the day (the rest he will eat and drink)

The Brain will be preserved by saving the connections the synapse had and connecting the new synapse in the same way. Let's say this works with 85% accuracy and always for the important part (close relatives, partner, values/character).

This can be repeated to arrive in edge cases 1 out of 10 million at 6 000 years. Most elves only reach about 350 to 600 years. Oh and mutations of the embryos are kept in check by comparing the embryos. Let's say only 1 of 1 million mutations gets activated per embryo.

Now I wanted to know if this is feasible or not.

Completely replacing the body will be

1. Resource consuming and


2. Dangerous.

Resources

To entirely replace the body within three to four years, the metabolism would have to be in overdrive. Even in the best case scenario, real humans can't even beat 7 years in terms of body regeneration. Those are 7 years of natural sleep-wake cycles when said human can choose any of sixteen average waking hours to have food. Your elves, even at ninety percent of the day would only have two hours and twenty four minutes to eat. Their stress levels just to get a snack after waking up would rival those of the antechinus in its mating rituals- and it dies at the end. Plus, the amount of water they would need to sustain this would be gargantuan. Even when those requirements are met, what about when the GI tract is regenerating from that of an embryo?

Danger

Cancer. They are regenerating their bodies very quickly and in large chunks. Looking at cells in our bodies that generate very quickly, we find high cancer rates. Cancers in the GI tract and skin are some of the most common in part because the cells there generate very fast. Cancer is the most dangerous risk, but there are others as well. If your elves are around lead (or any other developmentally harmful chemical), they could end up with a messed up body for the next 60 elf years.

But there is still hope for great longevity

Maybe the elves don't need something as complicated as generating whole bodies. A few alternatives to longevity:

• 
  Telomerase to prevent aging of the DNA


• Many copies of p53 to help fight cancer. Just look at elephants.


• A slower metabolism is optional. This works for many animals, mostly fish and reptiles.

I think you aren't talking about embryo's, but stemcells. The embryo starts with splitting itself into stemcells that can specialize into anything, and some of these stemcells are still present in adult humans right now and science is using them to learn and create new organs, they can already create individual cells.

Renewing parts of the body with stemcells could be possible, but it would be immensely complex. You need to migrate the stemcell through the body to the right spot, ehich is possible but not exactly accurate. Then you have the cell replicate to the right celltypes and need a complicated set of checks and balances to make sure old cells die and are replaced without interfering with the body's normal functioning.

Then theres the nervous system with the brain and spine as its centerpiece. The brain is a tricky thing and I got taught that the brain is both extremely set in its ways with nerves that carry specific tastes and things and on the other hand extremely malleable allowing parts of the brain to take up more space or even managing to lose half of the brain and have lots of those functions be managed by the remaining half. So potentially you would be able to have a piece of brain specifically for storing information of a brain area that is being rejuvinated, upon copying the old area gets shut down (to prevent interference) and a few bypasses to that brain area are made. Expect sometimes a slower response for brain area's that are stored on the temp storage brain. Still, you are looking at accuracy of the migrating stemcells and an even more complex system for replacing. With skin or bone its not a problem if it accidentally replaces a bit too much, with brain or nervous systems it could erase an important reflex, memory, muscle action or even cut the connection between parts of the body.

What you're describing is in effect an internal, biological form of gene therapy, an experimental medical treatment that seeks to treat or cure disease by altering the genes slightly to make the person being treated more resistant to the disease in question.

The problem is that we don't really understand what causes aging just yet, but one theory relates to a component of DNA called Telomeres, which appear to shorten with each replication of that DNA, ultimately putting a limit on the number of replications that can occur within an organism. The link also gives a wide range of different aging theories, all of which may assist you with forming your own conclusions regarding your answer.

To me though, the single biggest issue here would be longevity of the 'embryos' within your elf. It is generally believed in scientific circles that women are born with all their possible eggs within them, although there's been some recent debate about this given the discovery of stem cells within the ovaries, but in any event, women are born with a LOT of eggs inside them. The problem is, they start to die off immediately and continue doing so. By the time a woman reaches menopause, the few eggs remaining to her are more or less unviable. IVF has cheated this and allowed older women to have children by re-implanting eggs that have been harvested previously and fertilised, but generally speaking, a woman's eggs are not going to last 100 years, let alone 600, and your elf will suffer the same problem.

At the end of the day, especially in a warm blooded species, all parts of the body are going to be subject to entropy to a greater or lesser degree and given the sophistication and delicacy of DNA, the odds of keeping renewal gene pods inside a warm body for centuries, not subject to the normal renewal processes of the body and not subject to normal biological breakdown are remote.

In addition to this, there are two other factors that you really need to consider. Current natural DNA replication methods have many checks and balances built in already to stop errors (read as mutations) being introduced. These are not perfect, but given the amount of work they do over the course of a human lifetime, they're VERY reliable. Your design effectively hacks that process once every 60 years or so and feeds it a new template, which introduces all sorts of risk vectors. For one thing, diseases now have a new mechanism that they can exploit to get DNA to replicate of a different template completely, potentially introducing a runaway cancer scenario that effectively uses the body of the elf as raw material for the production of cancer cells on a massive scale.

Additionally, memories are even trickier. The problem is that we really don't know how they're laid down or stored in the brain, despite a lot of research in this area. It's possible that memories are just encoded electrical circuits in the brain, in which case you really don't want 'renewal' in that part of your body as it could potentially cause massive disruption. If memories are somehow encoded into the cells or into the pattern of connection between brain cells, renewal could be even more disruptive to memory, personality, etc.

In short, you're trying to bypass the natural aging process by internally storing cells that somehow bypass the aging process. Is it possible? Yes. But, it's highly unlikely and would involve organic 'storage' mechanisms that have yet to evolve despite them having a material benefit to procreation before longevity.