The other argument I have seen with this is that extra copies of DNA segments are "stored" DNA for future use to be brought out when needed, even if they have to be combined with segments from other "stored" DNA to make the necessary new genes.
That would have to be some kind of super-duper-polyploid person, with a repression mechanism to repress all the unwanted genes (to be transcribed in the future), a magical repair system to make sure none of those genes get degraded by random mutations, a recombination mechanism that replaces the new gene with its homologue (old gene) while completely degrading the latter, a mechanism to completely vanish all of the proteins specific for the activities above, and do all that in 4500 years. That is insane!
BTW: I think homologous recombination is a mechanism by which the cell repairs broken DNA (both strands) by pairing it with its homologue on the other chromosome and 'filling in the blanks' use recombinational methods.
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