So there's this man that was born 1,000 years ago, but today he's still living and he's (biologically) 28 years old. He just stopped aging at that age.

He is not immortal. He has been hurt in wars. He bleeds and hurts like everybody. He would die if he just jumps off a building, but he can't age, and he's never been sick (not even a fever). He also preserves the sensory apparatus (sight, hearing, touch, etc.), the strength and the memory of a 28 year old.

I'm looking for answers to how this may actually happen, non science-fiction or alienated theories. I'm not looking for scientific or technological INTERVENTION in any way, since there was none of those when he was born. I'm looking for 100% natural biological explanation for this planet that can apply to ancient or medieval times; mutation, junk DNA, or anything that CAN make it possible, logical and perfectly explainable (even if its too crazy to imagine, as long as it's -humanly possible-).

Also, he could have been born that way (though we'd have to explain why he raised normally til his 28's), or could have had an incident during his raising or when he turned 28.

Also, would there be other biological implications? Like eating or sleeping disorders? Or maybe he wouldn't need to eat or sleep at all? I guess it all depends on the chosen explanation.

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    $\begingroup$ Hi Cesar, welcome to Worldbuilding! This question has been discussed before. Basically, there are issues with human organs that don't regenerate and don't heal properly (teeth, eyes, cartilage, vascular plaque) for which some new regenerative mechanisms need to be invented. $\endgroup$
    – Alexander
    Feb 21, 2020 at 19:31
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    $\begingroup$ It's simple, he's a nerd. Nerds like us have no life, and that which is not alive cannot die. That's why NERD is an acronym for Nobody Ever Really Dies. $\endgroup$ Feb 21, 2020 at 20:48

6 Answers 6


There is a lot of money currently being invested by your friendly silicon valley billionaires in the hope that if we take the right drugs and supplements, which affect the correct genes, that aging will be arrested or even reversed.

So you can just go ahead and say your character got lucky with some genetic mutations which extend his telomeres or something, and you're good.

Doubtlessly, aging is a biological process, and with sufficient knowledge of biology man will one day become functionally immortal as you describe.


There is no real reason to suppose that aging will be easy to fix. This is because its not simply a matter of restoring a lost ability. Bodies have never been immortal.

Once upon a time, our ancestors reproduced by dividing in two. Obviously, if you're a single cell, you have to be immortal in order to reproduce. These immortal cells are called the germ line.

Eventually the single cell evolved to surround itself with other cells, all working together to make sure that germ line cell could reproduce.

Those other cells were expendable. They are body cells. But our gametes (egg, sperm) are part of an immortal cell line (your germ line) that goes back to the first cell that ever was.

Our bodies, however, have never needed to be immortal, as long as the germ line continues on. So even though they all come from immortal germ line cells, as evolution continued body cells quickly lost their ability to be immortal.

Only the simplest animals (some jellyfish for example) are able to fully repair their bodies.

The more complex bodies have become, the more difficult they are to maintain, and evolution has never had a reason to worry about what happens to you after your children have grown into functional adults.

From the perspective of your immortal reproductive cells, you are expendable, like a car. You can maintain your car, replace parts, but eventually you have to get a new car.

That is the way your body is in relation to your germ line. When you have a child your germ line gets a new body and leaves you behind.

Unfortunately this means things look pretty bad for our chances of finding a fountain of youth.

Additionally, it is safe to say that the chances of a combination of mutations resulting in an immortal individual is extremely slim. Its not just a matter of changing a few things, its a matter of adding huge amount of genetic material to accomplish all of the following things:

  • Repair or replacement of body parts that are not actually made of cells. (parts of teeth, parts of eyes, parts of bones, parts of connective tissue) AND full removal of damaging plaques in the brain and arteries. -----> this requires a bunch of new genetic processes that no animal has. (note that immortal jellyfish don't have teeth, eyes, bones, or much of a brain)

  • Drastically increased resistance to cancer, dementia, and other diseases that are associated with aging but not directly caused by it. ------> The longer you live, the more likely you'll eventually get cancer, even if you don't age, your cells are still accumulating damage from free radicals, UV rays and random DNA transcription mistakes. New genetic processes are needed.

  • Better immune system. ------> Living 1000 years means living through multiple plagues, etc. Without a better immune system that is unlikely. You could say they just got lucky, but if not then they need genetic changes for this too.

  • Increased Neuroplasticity ------> While not needed to simply live, it would be important for the character to retain his/her youthful ability to learn new ideas and adapt. By the time someone is 28 they are pretty set in their ways, but living 1000 years means they will need to reinvent themselves over and over, and learn new languages and skills multiple times if they are to appear "normal" to the people around them and not get lynched. This will require some genetic changes as well.

  • The ability to regrow limbs, heal without scarring. -------> scars are the body's way of just patching over an injury as soon as possible. If you're mortal it doesn't really matter if you accumulate scars and unhealed injurie, but for an immortal the accumulated scars would eventually be debilitating. Fixing this issue would require new DNA dedicated to enabling full healing of any and all injuries that are not immediately fatal, including non-traumatic injuries and internal injuries like heart attacks and strokes.

There are far too many changes needed for this to have happened in one single individual through a lucky combination of mutations. Baring divine or extraterrestrial tampering, there is only one plausible way this could EVER have happened naturally: your character is from an ancient race of individuals that only reproduced when they were old.

Only in this way would evolution be able to act effectively to add the hundreds or thousands of new genes needed to allow for a long lifespan.

Each generation of individuals would have to reproduce ONLY at the last third of their life.

First, selection would favor females with extended reproductive fertility.

Then it would favor those who lived long enough to take care of their children.

Gradually, over many thousands of generations, lifespans would begin to expand to hundreds of years.

Any early breeding would have ruinous consequences for the program. One can imagine the kind of appalling social structures this would necessitate. No sex until you're 600. Early babies must be killed. Etc...

In order to sustain this breeding program in the face of overwhelming competition from faster-breeding normal humans who would overwhelm them and kill them in normal circumstances, they would have to have been insulated since prehistoric times by some kind of natural barrier. Perhaps they lived on a large island or in a hidden valley behind a high mountain range.

Obviously there are no such places around today, but since your character is 1000 years old, you could say they were found by the rest of civilization 1000 years ago, and subsequently destroyed by outsiders, leaving your character as the only remaining immortal.


You can't beat Death without cheating

Sorry. Immortality is pretty attractive, but there's no way for a human being to stop aging. Aging is composed of many factors, but if you want to boil it down to the basics, it's all the fault of the entropy. Every exchange of energy leads to an increase in randomness, and the only way to beat that is by creating new life, i.e. having children.

Within the very bloodstream of your human, his cells' mitochondria are hard at working, churning out ATP for him to use. But that very process using very dangerous oxygen radicals as the final stage in a redox reaction alongside the relatively benign H20 water vapor you breath out. Those radicals build up and leave damage all over the cells. Every wound he takes needs healing, but every time the body expends energy to heal the damage, it can't make the resultant tissue as good as the original. Same thing with the organs. Human organs, taken care of perfectly, can last a while, but the heart is getting beaten all this time, no rest even for a second. A human heart can't last 1000 years with no rest, it's simply not possible. And all this while, the DNA within the replicating cells are getting more and more degraded. The body is very good at keeping DNA in pristine condition, but again, it can only do it for so long.

Aging, when it comes down to it, is merely the accumulation of stress on the body from all the various sources. That's why there's no one cause to aging, and no one way to beat it. We're getting better and better at taking care of humans and extending their lifespans thanks to medicine, but we can't halt aging without seriously cheating. And if you want a 100% all natural human being, that's not an option.


I was going to post this as a counter to the answer by @Halfthawed but I decided to put this in an answer instead.

As said, the reason for dying eventually is because the damage to organs piles up and cannot be repaired as well as it was before.

The same thing happens to cars though. We replace their parts.

Your immortal is a scavenger, harvesting organs. He feels a flutter in his heart and the next night you can see him in a back alley waiting for some 20-something to stumble out of a bar with his replacement heart beating in her chest.

He has an uncanny ability to take organ donations without rejecting their blood types. His cells merge with other cells readily, the new organ starts working again without skipping a beat. The old one is consumed and used for it's energy. More than likely, the victim's corpse is also cannibalized in some way.


Applying Ockham's Razor by making as few assumptions as possible, In other words, the simplest explanations work best. There is a simple explanation for a thousand year man who stopped ageing at twenty-eight.

But first let's look at the opposite situation. There is a medical condition known as progeria. persons with this condition undergo advanced ageing at young ages, For example, teenagers looking and acting like eighty year olds. Children with progeria rarely survive beyond the age of thirteen.

Progeria is a genetic condition affecting one in four million, irrespective of sex or ethnic background. This seems to be a matter of having the wrong genes.

Now man who hasn't aged for a thousand years may simply the equivalent of the opposite of progeria. A completely fortuitous combinations of genes that inhibits any further ageing pas the age of twenty-eight. This would be be a sufficient explanation to account for this condition. However, there are a few caveats.

Anyone with, let's call it, antageria (a condition that prevents or inhibits ageing), will also need to be blessed with biological mechanisms to preserve their bones, teeth, and skin. A thousand year old man, no matter how youthful, may have had false teeth for most of his life. Also, his knees and hips could be in terrible shape. The progressive accumulation of scar tissue will eventually him from breathing through the pores on his skin.

Now assuming this thousand year man has all these recquisite genetically based mechanisms, then he could still look like a twenty-eight year old. The simplest explanation is that he has the right combination of genes and than out of all the genetic variation in the human species there are rare combinations that can facilitate extreme longevity with inhibited ageing. Most other explanations are attempts at hand-waving on the basis of implausible guesswork.


The body is an amazing thing. When completely healthy, we never cease to amaze ourselves at what human bodies are capable of.

Fact: there are ancient written records of people living hundreds of years, sometimes nearly a thousand years. Many people no longer believe this, but there are still plenty who believe these records are true.

Now here comes the handwaving...

If only we could keep the human body completely, utterly, 100% perfectly healthy, it is capable of keeping itself forever in a state similar to that of a normal, modern human in their late 20's. Modern medical practice does not realize this because it has no perfectly healthy specimens. Everyone is of sub-perfection health.

Your immortal people could have come from a lineage of perfectly healthy humans. Ever since Adam and Eve started on the Genesis diet of "every seed-bearing plant and every tree that has fruit with seed in it," the lineage from Adam and Eve to your immortals has followed the diet strictly, and they have avoided the plants which became poisonous after The Fall.

The ancestry activities of this lineage also includes excellent exercise, plenty of sleep, and minimal stress. If anyone should stray too far from these perfect conditions for too long and destabilize their balance of perfection, they may lose their immortality.

Because they are so extremely healthy, it takes a lot more for one of these people to lose their immortality than it would for you or I to cause our health to fail. Their immune systems are so superior, their healing so extraordinary, that whatever a normal person might have to put themselves through to cause an organ to fail, these folks can put themselves through twice as much before becoming unhealthy and losing their ability. And their regeneration is so absolute that they can bring themselves to the brink of losing their immortality but fully recover as long as they return to the ways of their ancestors for a year.

Why are there not lots of these people all over the place since their descendants inherit this amazing gift? 1) As you said, they still die from non-aging causes. 2) It is just so hard to maintain a perfect lifestyle: many people did so long enough to have children but eventually fell off the bandwagon. Even after losing their prestigious ability, they are still so healthy that they may live for hundreds of years if they are careful.

Fortunately there is a way to generate new lines of immortals like this. If you can maintain a lineage of perfect health in every way for 7 generations then the maximum life span of each next generation after that will be longer than the one before, until finally the perfect human will emerge immortal. This usually takes about 77 generations of uninterrupted perfection.

Among some of the immortals there is a rumor that if they could maintain a line of 777 generations of immortals who never made any mistakes in upkeeping their health, that the resulting human body would have conscious control over its brain functions and DNA replication so that it could manipulate its own body to possess the features and abilities it desired.

Unfortunately, the closest anyone has ever come to this state of transcendence in modern history was Nostradamus who managed to restructure his brain functions to allow an extraordinary deduction ability and predict future events with it, but alas he was so greedy that he expanded his mental functions too far at the expense of other bodily functions which caused him to lose his perfect health and rapidly decline, though there was a cover up by a cousin which attributed his condition to gout and edema. His cousin feared that if any of the other immortals knew that they could accidentally kill themselves by abusing their transcendence that they might not try again.


The only way your character could completely stop the aging process is through:

  1. suspended animation technology for example cryogenic stasis would freeze and preserve the body for hibernation while other methods includes using chemicals for preservation.

  2. He is a cyborg that occasionally replaces certain bodyparts.

  3. He discovered a reverse aging chemical substance that could completely reverse the aging process.


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