I'm with the people who suggest it has to be a new mutation. Because if it has been around for thousands or millions of years, you have to ask these questions:
1. Is it hereditary? (Usual answer in SF is yes, it's genetic).
2. Is it useful? Particularly in a 'saving your life' way, or a 'making you life easier' way. (Usual answer in SF is yes, yes, yes, hell yes, and yes with bells on!)
3. If it is hereditary and useful, why hasn't natural selection er, naturally selected for it? (Just think of all the ways telepathy or telekinesis would make a caveman's life safer or easier).
4. Why have no animals got it? (Usual answer in SF is pseudo-intellectual, hippy dippy nonsense about only sufficiently 'enlightened' beings being capable of psi powers and/or the old lie about only using 10% of your brain. In the latter case, chimps should STILL be capable of psionics!)
For my "Hard Space" setting:
1. No. It only occurs in children whose mother has passed through Jump Space at least once during their gestation.
2. Standard Traveller psionics - can definitely save your life, especially if you have the rare Teleportation Talent...
3. It is a result of exposure to Jump Space (i.e. gestation in a mother who travels by a Jump-capable starship). No natural selection here.
4. See 3.
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