Disclaimer: I'm not a biologist or geneticist, so my knowledge on the following topics is limited. Feel free to point out any mistakes, but please be polite about it.
I'm currently planning a story where the entire human population is biologically immortal (meaning they can be killed, but they won't age after reaching adulthood or die of natural causes).
Here is my desired outcome / the conditions of the aforementioned immortality:
- Humans don't age anymore, so they won't die of old age (Edit: If necessary, replace 'eternal life' with 'very long life (1k+ years)'; thanks @CortAmmon)
- Cancer isn't a problem anymore (nobody gets cancer or cancerous/tumorous cells are automatically killed off by bodily functions or defective tissue can be cut out and the body will replace the missing parts with new, healthy tissue (see the regeneration capabilities below))
- Other diseases can still occur and restrain or incapacitate people for some time, but eventually the body will fight off any disease, even those that aren't curable to our current knowledge (like HIV/AIDS).
- The human body has increased regeneration capabilities, meaning wounds (even grave ones, such as a bullet in the head) will heal automatically to a certain extent, severed limbs will grow back (not within a day, but within a couple of years or decades (so no Resident Evil-level BS)). Therefore, the only way to kill/die permanently would be to destroy the body completely, e.g. burn it.
- Edit: It's fine (even preferred, to be honest) if severe brain damage results in memory loss and the victim might have to relearn basic stuff or is basically setback to infancy. Thanks @Samuel for pointing that out!
To sum this up, any human can live eternally unless their body is permanently destroyed. Let's call people who meet these requirements 'super humans' for the sake of this question.
OPTIONAL: Super humans can survive for a long or even unlimited amount of time without nourishment. I tend to think this is entirely impossible, so it's not a requirement.
These conditions must be inheritable, meaning if two super humans (or a super human and a normal human) have a child (which by the way is in no way limited, so super humans can have an infinite amount of children in an infinite amount of time, while pregnancies still take the usual ~9 months), this child will also be a super human.
Even though this is basically science-fiction at the moment, I want the means by which this is achieved to be plausible (or as plausible as possible) with what we currently know about the human body. So I'm thinking genome manipulation, for example introducing a dominant allele into the human genome which will allow the human's cells to produce telomerase which in turn can regenerate telomeres so cell division won't be limited. I know this raises other problems such as increased cancer risk over time, but it's fine with me to assume those can be solved via more gene manipulation, so that in the end there will be one set of (manufactured) genes that can be implanted in selected individuals to create a super human. It doesn't matter if those selected individuals will become super humans as well, the only thing that matters is that their children (and all their descendants) will be super humans
So, my question is: Is this scenario plausible (given our current, limited knowledge)? Monetary ressources and time aren't an issue.
If so: How would the super humans most likely be created? Would the manipulated gene be surgically implanted in fetuses, or in sperm, or in the mother's egg cells prior to impregnation? Or is there another method that I'm not aware of (as long as the 'super-humanism' is inheritable, I'm fine with an approach that doesn't involve gene manipulation)? And can the optional requirement stated above be achieved that way as well?
If not: Can I make any assumptions about future discoveries/inventions which would make it possible? Or which of the requirements stated above would I have to drop to make it possible? (The one I'd be the least reluctant to drop are the regeneration capabilities, in case that matters)
Bonus points if you can tell me what timeframe to assume for both the discovery/invention of the required genes and methods and the replacement of humanity by 'super-humanity'.