But all natural selection operates on existing mutations, which by your definition are now preadaptations.
Well obviously natural selection only acts on existing mutations, but it certainly need not act only on mutations whose existence precedes that of the selective pressures which render them beneficial.
I think what Jaderis was getting at was more the diversity latent in the population from accumulated non-lethal mutations.
I was not thinking of preadaptation in terms of a large pool of genetic variation but rather as a sort of micro hopeful monster scenario with some sort of neutral trait, not something like a SNP, was present and maintained in the population until it became beneficial.
I'm also not sure if Jaderis is really focusing on the maintenance of a trait within the population or not, when he says...
Jaderis writes:
I suppose the same thing could be said about mutations that in previous generations would have been damaging, but eventually came along at a time where they became beneficial.
This rather suggests a scenario where particular mutations are reocurring
de novo which is a different scenario again.
TTFN,
WK