Is “convergent evolution” a convenient escape clause for evidence that contradicts evolution?

Evolutionary theory has a classification scheme that cannot lose.  Darwin’s original tree diagram described “divergent evolution,” a process beginning with speciation followed by the accumulation of variations that make the two branches more and more dissimilar over time.  Animals with similar structures on the same branch are said to have “homologous” traits, because they derive from the same common ancestor.  But the living world is filled with traits that resemble each other on different branches.  What caused that?  Ah, the evolutionist replies: those traits are due to “convergent evolution.”  The similarities are “analogous” traits, because they do not derive from the same common ancestor.  With this classification scheme, evolution explains everything: if similar animals are related, they evolved; if they are unrelated, they evolved.  Is this a description of reality, or rather a convenient strategy for rendering evolution immune from falsification?  Here are some recent examples of “convergent evolution” from the literature.

Jelly-Bird:  PhysOrg wrote, “Ion selectivity in neuronal signaling channels evolved twice in animals.”   Sea anemones and birds have complex channels in their cell membranes called voltage-gated sodium channels, responsible for passing signals along nerves.  Yet their respective branches on the tree of life supposedly separated 600 million years ago.  The channels in the marine invertebrates “differ from those found in higher animals, yet show the same selectivity for sodium.”  Thus, “This study shows that different parts of the channel changed in a convergent manner during the evolution of cnidarians and higher animals in order to perform the same task, namely to select for sodium ions,” the article alleged. “This demonstrates that important components for the functional nervous systems evolved twice in basal and higher animals, which suggests that more complex nervous systems that rely on such ion-selective channels could have also evolved twice independently.”

Jelly-Man:  Nature News claims that muscles, too, evolved twice.  In “Evolutionary biology: Muscle’s Dual Origins” (12 July 2012), Andreas Hejnol said, “Jellyfish move using a set of muscles that look remarkably similar to striated muscles in vertebrates.  However, new data show that the two muscle types contain different molecules, implying that they evolved independently.”  Adding to the puzzle is the fact that comb jellies, on a different branch, also have striated muscles, while most other invertebrates do not.  “Whether this comb jelly’s striated muscle is related to that of jellyfish or vertebrates, or represents another convergent evolution event, remains to be determined.” ….

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