Synch
Since: Jul, 2012
Oct 17th 2013 at 6:15:23 AM
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Yes, the book's explanation makes perfect sense to me. I'm no scientist and I don't know how big a role Earth's natural radioactivity plays in causing mutations, but you do need genetic mutation (combined with natural selection) to achieve evolution. Otherwise, you're just shuffling the same genes back and forth.
To be strictly accurate, Asimov posited (through Mandamus) that the presence of radioactivity in relatively minor amounts in the Earth's crust, compared to terraformed worlds that lacked uranium and thorium, promoted a higher mutation rate. This would broaden the distribution of alleles subject to a selection pressure and presumably this "choose from more alternatives" mechanism drove evolution more strongly than on non-Earth planets.
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