There are many theories of evolution, each of which disproves the others.
Putting aside beneficial mutations, the contention that mutations are always harmful ignores the existence of silent and neutral mutations, which have no appreciable impact upon an organism.
Silent or synonymous mutations, which involve the substitution of one (anti)codon for another that codes for the same amino acid. For instance, the DNA anticodons AAA and AAG (RNA codons UUU and UUC) both code for phenylalanine, so a point mutation that changes the one to the other has no impact on the protein that stretch of DNA codes for. As Mark Ridley points out, a full 70% of substitutions of the third base in (anti)codons produce a silent mutation, though the effect is 0% and 4% for the first and second bases (Ridley 1993:74).
Even where a mutation does cause a replacement of amino acids, the impact upon the protein in which the replacement occurs will not necessarily be important to the organism. This may be because (i) the replacement amino acid is similar enough to the replaced one, or (ii) the replacement occurs at a locus of no importance to the activity of the protein. In this case, we refer to the mutation as a neutral mutation rather than a silent one.
Criticism of evolution on the basis of the alleged universal harmfulness of mutations is, therefore, a complete nonstarter. Dissuaded from this criticism, creationists tend to retreat to the weaker, but equally false, claim that mutations are never beneficial.
Ridley M. 1993. Evolution. Boston: Blackwell Scientific Publications.
Last updated: 21 Mar 2008
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