We were presented with this picture of small fish A. Mexicanus tetra, which is able to switch from normal appearance to cave-adapted in few generations.
It is argued by creationists that such cases prove that evolution is not able to make big changes and adaptations, and all information is already included in genome; the phenotype just switches as required.
Well, first of all I'd like to see some kind of evidence for this switching mechanism, rather than it being caused by mutation and selection. If the switching mechanism existed, wouldn't it happen after
one generation, after the first generation of fish spent a lifetime in the dark? Or indeed within one generation, like tanning? Instead, you say "a few" generations. How few?
In the second place, even if this mechanism exists, there's a huge logic fail there from the word "prove" onward. It's like saying: "John often walks to the shop on the corner and back, it takes him 10 minutes. Such cases prove that all journeys are short, and that no-one takes long transatlantic flights on so-called "planes" as you guys claim". But the existence of one mechanism to move short distances does not
prove that there is not another mechanism to move long distances.
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