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Exactly my point. The DNA of the fast animals is already in the genepool of the multipurpose genome. A bit of shuffling, a bit of (non-)random mutations and voila a "new" faster population after a couple of generations! New genes? NO. Different organisation? Maybe. Distinct gene regulation? Sure.
Unfortunately, I think you missed my point. In that particular example, the phenotypical traits for "fast" and "slow"
were already present in the genome. I certainly agree that the gradual shift in frequency between "fast" and "slow" alleles in the population under selection pressure doesn't represent new genetic material. However, these genes are not "turned on" by selection - they are already expressed phenotypical variations. However, the variations are introduced by random mutation - not directed by the environment. If random mutation HAD NOT already produced the variation, there would have been nothing for natural selection to act upon in the first place. If you look at it in a different way, if there were no variation - no "fast" alleles that provided an advantage in this case - the population would go extinct. Since we can see this type of local extinction occurring regularly (c.f., "sanctuary effect" and "island effect" in the context of deforestation, for instance), this is a pretty solid statement. Hence, your concept of a multipurpose genome that provides genes which are "turned on" due to environmental effects has NOT been observed.
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Yes, I remember. It was a joke, wasn't it? And that is why everyone is wearing Nikes, nowadays?
Yes, it is a joke. However, it is quite illustrative of how natural selection works. Consider, in context: if bear predation was a significant selection pressure and the posession of tennis shoes (the Nike trait?) was the variation that gave an organism increased marginal fitness against non-tennis-shoe-wearers, then YES, everyone would at some point be wearing Nikes - because everyone who didn't have them would have been eaten. Of course, that means the bears would either die out OR a lucky mutation would give them some advantage (e.g., roller-skates) in order to keep up the evolutionary arms race. Losers in evolution are called "extinct". Our bears would accidently have to have received roller-skates to survive. If they didn't, they'd be a historical footnote.