I've just came up with an idea. Just want to know if it may exist.
Imagine that there is some organism. It may be kind of humanoid, bird, insect, etc.. It has a special organ. When it detects death (or some other message?) of organism, it cools down brain, and starts to consume rest of body, creating a new child of that organism? Like organ that converts old adult to child, while keeping knoweldge?
So, is it possible? How can it detect death? Or what it may detect?
I've just came up with an idea. Just want to know if it may exist.
It should theoretically be possible. But also very hard. And not necessarily worth it.
The easiest way to think about it I think would be an egg. A self-contained box full of nutrients, in which an animal can grow.
I think that practically you would not want to start at the moment of death. If only at the moment of death is the new organism is initiated from a single cell (one genetically the same as the old), it would essentially race against decomposition to make use of the rest of the body, and would stand no chance to save the information in the central nervous system before it is lost.
So my version of the phoenix organ does not defend against sudden death. Rather, it keeps a small asexually produced embrio in stasis (and possibly produces a new periodically), and when it detects that the organism is about to become unviable (the actual detection is done by the brain. If this being is intelligent, it might even learn to trigger it intentionally (say on cancer diagnosis)), it initiates the Transfer. Most of the old body is quickly athropied, its materials being transfered into a sterile sack, from which the new can draw nourishment. In the meantime the nervous system is ablaze as the rapidly growing brain of the embrio tries to accumulate compressed information from the old brain.
The critical question is the length of this process. If it takes days or weeks, only slowly progressing disease and old age can be countered this way. But the simpler the organism is, and the more resources it transfers into the embrio beforehand, the faster it gets. So if for example the main fat reserves need not be physically moved (the phoenix-sack doubles as the fatty tissue in the old body), and the brain is small and stupid, the Transfer might be ready before the wounded animal bleeds out.
That's rather unlikely. You see, the brain is what controls our body and metabolic processes, but just like the rest of the body, it needs these processes to survive, especially when it comes to oxigenation. What you're asking is for the body to deconstruct every part of itself except for the brain and from that create a child, a process that already is in itself unlikely, as humans are very complex creatures with highly specialized cells, and thus forcing a multiplication of many of these cells is a dangerous process that may result in cancer (that's also a reason why a human cannot regrow a lost limb or organ)
The second problem is senescence. Senescence is essentially cellular aging, and is mostly associated with the shortening of the telomeres (protecting sheaths that are reduced every time a cell divides in 2). Although not as noticeable in all animals, senescence is apparent in humans, and is one of the main reasons we can't live forever (apart from other natural problems characteristic of aging that usually kill us before we can die from true natural death from overly damaged DNA).
But let's analyze assuming it somehow happened. So essentially you're recycling an 60 year old's body back into a young one (let's say a 14 year old). First and foremost, you'll need a cocoon, otherwise you'll be relying on your skin to keep your now liquefied cell soup of a body, and that won't likely end well. For a certain period, the heart and lungs will be in the middle of deconstruction while the new heart and lungs are made, meaning that for a certain period, your body will not have oxygen flowing through it. No oxygen, no respiration, no respiration, no ATP(energy your body uses to function), not enough ATP, you'll die before the new respiratory and circulatory systems are online. young one, which would in itself require a lot of energy. The second issue is that your brain would have to remain some time without oxygenated blood flowing through it, and unlike the rest of the body, the brain is extremely sensitive to a lack of oxygen, meaning high risks of this organ being damaged mid-recosntruction.
But now let's assume it all went well, no major problems happened and you successfully survived the cocooning and reformation. Congratulations, you're now a 14 year old with the genome and brain of a 60 year old,and just like dolly, the cloned sheep created using the cells of an adult sheep, you'll have very similar problems: you'll age a lot faster, your brain will be still at the risk of mental issues that come with old age, as it's cells are still 60 years old,your DNA has telomeres shorter than any other boy at your current age, you still have a higher risk of developing cancer and if you're a woman, it's likely you might have problems having a child, since your gametes too are still 60 years old.
So, is it possible for a person to act like a caterpillar and regress their own age? From a realistic perspective, even if it was (currently we can't even regrow a pinky finger, let alone our entire bodies) the cons seem to outmatch the pros. It's true that some jellyfish are virtually biologically immortal, but these jellyfish are much more simpler organisms. As our current science goes, simply avoiding senescence (as we see with some human cancer cells) or reversing aging through other means might be a more plausible solution.
Firstly you would have differentiate between 'slow' and sudden deaths. I suppose you could hypothesize the existence or an organism that could detect via internally secreted chemical messages the immanent approach of death via senility/old age or infection. Sudden accidental death (falling off a cliff) or predation (being pounced on by the local top carnivore) no way.
Assuming your only dealing with the former I would suggest the following. Perhaps all members of the species normally reproduce sexually and lay eggs. However they have also retained the ability to reproduce asexually and from birth store one such egg internally in torpor so it never fully develops until needed. That egg is basically genetically identical to the parent.
After detecting the immanent approach to its own demise the organism finds a secure den and goes into torpor - the process 'awakening' the stored egg at the same time. The egg then develops and hatches within the 'parent' whereupon it commences to consume the parents body from the inside out leaving the vital organs such as heart and lungs plus brain till last. (BTW this is what what many predatory wasp lava do when they hatch on the bodies of prey stung into torpor by their mother.)
Next comes the hard (impossible) bit. Having consumed its parent and grown to the point where it can survive independently the sub-adult consumes/engulfs/injects new neurons into the adult brain. Whatever the process the end result is the overlay of the new 'young' neural network with the memories of the old. (Note - to do this the brain of your life form would have to be structured in a totally different way to mammalian brains as we understand them). More like an insects perhaps or even a plant with memories exchanged/stored via things like complex biochemicals (DNA/RNA analogues?) that can be passed from one nerve cell to another.
How extensive or successful the process is is up to you. Maybe it just absorbs basic memories like familial linkages, migratory routes, dangerous predators i.e not much more than instinct would provide, maybe it remembers where it was up to in the book it was reading before it died?